Climate change: Difference between revisions
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[[Image:Instrumental_Temperature_Record.png|thumb|250px|right|Global mean surface temperatures 1856 to 2004]] |
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[[Image:Global Warming Map.jpg|thumb|250px|right|Mean temperature anomalies during the period 1995 to 2004 with respect to the average temperatures from 1940 to 1980]] |
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'''Global warming''' describes an increase in the [[Historical temperature record|average temperature]] of the [[Earth's atmosphere]] and [[ocean]]s. The terms ''global warming'' or ''anthropogenic global warming'' are also used to describe the [[theory]] that increasing temperatures are the result of a strengthening [[greenhouse effect]] caused primarily by man-made increases in [[carbon dioxide]] and other [[greenhouse gas]]es. The natural greenhouse effect keeps the Earth 30°C warmer than it otherwise would be; adding carbon dioxide to an atmosphere, with no other changes, will tend to make a planet's surface warmer; the question is, ''by how much?'' |
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The [[scientific opinion on climate change]], as expressed by the [[UN]] [[Intergovernmental Panel on Climate Change]] (IPCC) and explicitly endorsed by the national science academies of the [[G8]] nations, is that the average global temperature has risen <!-- The following is an approximate 95% confidence interval, please DO NOT replace by 0.4-0.8 -->0.6 ± 0.2 °[[Celsius|C]] since the late 19th century, and that "most of the warming observed over the last 50 years is [[Attribution of recent climate change|attributable to human activities]]". A [[list of scientists opposing global warming consensus|small minority of qualified scientists]] contest the view that humanity's actions have played a significant role in increasing recent temperatures. Uncertainties do exist regarding how much [[climate change]] should be expected in the future, and a hotly contested political and public debate exists over what actions, if any, should be taken in light of global warming. |
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Based on basic science, observational sensitivity studies, and the [[General circulation model|climate model]]s referenced by the IPCC, temperatures may increase by 1.4 to 5.8 °C between 1990 and 2100 [http://www.sciencemag.org/cgi/reprint/309/5731/100.pdf]. This is expected to result in other climate changes including rises in [[sea level rise|sea level]] and changes in the amount and pattern of [[precipitation (meteorology)|precipitation]]. Such changes may increase extreme weather events such as [[flood]]s, [[drought]]s, [[heat wave]]s, and [[hurricane]]s, change [[agricultural]] yields, or contribute to biological [[extinction]]s. Although warming is expected to affect the frequency and magnitude of these events, it is very difficult to connect any particular event to global warming. |
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== Overview == |
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{{Sidebar|'''Terminology''' |
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In common usage, the term "global warming" generally implies a human influence — the more neutral term [[climate change]] is usually used for a change in climate with no presumption as to cause and no characterization of the kind of change involved, such as the [[Ice Age]]s. Note, however, that there are important exceptions to this: the [[UNFCCC]] uses "climate change" for human caused change and "climate variability" for non-human caused change [http://www.grida.no/climate/ipcc_tar/wg1/518.htm]. Some organizations use the term "anthropogenic climate change" to indicate the presumption of human influence. |
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See also: [[Glossary of climate change]] |
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}} |
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The [[scientific consensus]] on global warming is that the [[Earth]] is warming, and that humanity's [[greenhouse gas]] emissions are making a significant contribution. This consensus is summarized by the findings of the [[Intergovernmental Panel on Climate Change]] (IPCC). In the [[TAR (IPCC)|Third Assessment Report]], the IPCC concluded that "most of the warming observed over the last 50 years is [[Attribution of recent climate change|attributable to human activities]]". This position was recently supported by an international group of science academies from the [[G8]] countries and [[Brazil]], [[China]] and [[India]] [http://www.royalsoc.ac.uk/displaypagedoc.asp?id=13057]. |
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Over the past century or so the global (land and sea) temperature has increased by 0.6 ± 0.2 °C [http://www.grida.no/climate/ipcc_tar/wg1/figspm-1.htm]. The [[effects of global warming]] are increasingly visible. At the same time, atmospheric [[carbon dioxide]] has increased from around 280 [[parts per million]] (by volume) in 1800 to around 315 in 1958 and 367 in 2000, a 31% increase over 200 years. Other greenhouse gas emissions have also increased. Future CO<sub>2</sub> levels cannot be predicted with any precision, since they depend on uncertain economic, sociological and technological developments. The IPCC [[SRES]] gives a wide range of future CO<sub>2</sub> scenarios [http://www.grida.no/climate/ipcc_tar/wg1/123.htm], ranging from about 0.04 to 0.1 % by volume by 2100. |
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[[General circulation model|Climate model]]s, driven by estimates of increasing carbon dioxide and to a lesser extent by generally decreasing [[sulfate|sulphate]] [[aerosol]]s, predict that temperatures will increase (with a range of 1.4 to 5.8 °C for change between [[1990]] and [[2100]] [http://www.grida.no/climate/ipcc_tar/wg1/339.htm]). Much of this uncertainty results from not knowing future CO<sub>2</sub> emissions, but there is also uncertainty about the accuracy of climate models. [[Climate commitment studies]] predict that even if levels of greenhouse gases and solar activity were to remain constant, the global climate is committed to 0.5 °C of warming (some model results are as high as 1.0 °C) over the next one hundred years due to the lag in warming caused by the oceans. |
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Although the combination of scientific consensus and economic incentives (especially for Russia) were enough to persuade the [[List of Kyoto Protocol signatories|governments of more than 150 countries]] to ratify the [[Kyoto Protocol]] - there are issues about just how much greenhouse gas emissions warm the planet. Uncertainties remain and have been emphasized by some politicians, and others questioning the costs needed to [[mitigation of global warming|reduce future global warming]]; however, the [[business position on climate change]] is increasingly changing to accept global warming as both real and anthropogenic, and that action such as [[carbon emissions trading]] and [[carbon tax]]es is needed. The scientific consensus is questioned by a small minority of scientists. |
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==Warming of the Earth== |
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[[Image:2000_Year_Temperature_Comparison.png|thumb|right|Two millenia of temperatures according to different reconstructions, each smoothed on a decadal scale. The unsmoothed, annual value for 2004 is also plotted for reference.]] |
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Relative to 1860-1900 the global (land and sea) temperature has increased by 0.75 oC. Temperatures in the lower [[troposphere]] have increased between 0.12 and 0.22 °C per decade since 1979. Over the past 1-2 thousand years before 1850 the temperature has been relatively stable, with various (possibly local) fluctuations, such as the [[Medieval Warm Period]] or the [[Little Ice Age]]. |
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The period of time over which one is interested in change may vary according to the focus of the user of the term and the datasets available for investigation. [[Temperature record]] holds a discussion of the various records. An approximately global [[instrumental temperature record]] begins in about [[1860]]; contamination from the [[urban heat island]] is believed to be small. A longer-term perspective is available from various proxy records for recent millenia; see [[Temperature record of the past 1000 years]] for a discussion of these records and their differences. [[Attribution of recent climate change]] is clearest for the most recent period (the last 50 years) for which the most detailed data is available. [[Satellite temperature measurements]] of the tropospheric temperature date from 1979. |
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==Causes of global warming== |
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{{seemain2|attribution of recent climate change|scientific opinion on climate change}} |
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[[Image:Carbon Dioxide 400kyr.png|thumb|right|250px|[[Carbon dioxide]] during the last 400,000 years and the rapid rise since the [[Industrial Revolution]]]] |
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The climate system varies both through natural, "internal" processes as well as in response to variations in external "forcing" from both human and non-human causes, including changes in the Earth's orbit around the Sun ([[Milankovitch cycles]]), [[solar activity]], and volcanic emissions as well as greenhouse gases. See '''[[Climate change]]''' for further discussion of these forcing processes. Climatologists accept that the earth has warmed recently. Somewhat more controversial is what may have caused this change. See '''[[attribution of recent climate change]]''' for further discussion. |
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Atmospheric scientists know that adding [[carbon dioxide]] (CO<SUB>2</SUB>) or [[methane]] (CH<sub>4</sub>) to an atmosphere, with no other changes, will tend to make a planet's surface warmer. Indeed, [[greenhouse gas]]es create a natural [[greenhouse effect]] without which temperatures on Earth would be 30°C lower, and the Earth uninhabitable. It is therefore not correct to say that there is a debate between those who "believe in" and "oppose" the theory that adding CO<SUB>2</SUB> or CH<SUB>4</SUB> to the Earth's atmosphere will result in warmer surface temperatures on Earth, on average. Rather, the debate is about what the ''net'' effect of the addition of CO<SUB>2</SUB> and CH<SUB>4</SUB> will be, and whether changes in water vapor, clouds, the biosphere and various other climate factors will ''cancel out'' its warming effect. The observed warming of the Earth over the past 50 years appears to be at odds with the skeptics' theory that climate feedbacks will cancel out the warming. |
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<div style="clear: both"></div> |
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===Greenhouse gas emissions=== |
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[[Image:Major greenhouse gas trends.png|thumb|right|350px|Greenhouse gas trends]] |
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Coal-burning power plants, automobile exhausts, factory smokestacks, and other waste vents of the human environment contribute about 22 billion tons of carbon dioxide and other [[greenhouse gas]]es into the earth's atmosphere each year. Animal agriculture, manure, natural gas, rice paddies, landfills, coal, and other sources contribute about 250 million tons of methane each year. About half of human emissions have remained in the atmosphere. The atmospheric concentrations of CO<SUB>2</SUB> and CH<SUB>4</SUB> have increased by 31% and 149% respectively above pre-industrial levels since 1750. This is considerably higher than at any time during the last 420,000 years, the period for which reliable data has been extracted from [[ice core]]s. From less direct geological evidence it is believed that CO<SUB>2</SUB> values this high were last attained 40 million years ago. About three-quarters of the anthropogenic emissions of CO<SUB>2</SUB> to the atmosphere during the past 20 years is due to [[fossil fuel]] burning. The rest is predominantly due to land-use change, especially [[deforestation]] [http://www.grida.no/climate/ipcc_tar/wg1/006.htm]. |
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The longest continuous instrumental measurement of CO<sub>2</sub> mixing ratios began in 1958 at [[Mauna Loa]]. Since then, the annually averaged value has increased [[monotonic function|monotonic]]ally from 315 [[parts per million|ppmv]] (see the [[Keeling Curve]]). The concentration reached 376 ppmv in 2003. South Pole records show similar growth [http://www.cmdl.noaa.gov/info/spo2000.html]. The monthly measurements display small seasonal oscillations. |
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===Alternative theories=== |
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====Solar variation theory==== |
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[[Image:Solar-cycle-data.png|thumb|right|20 years of solar output]] |
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{{main|Solar variation theory}} |
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Various [[hypothesis|hypotheses]] have been proposed to attribute terrestrial temperature variations to [[solar variation|variations in solar output]]. |
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In the IPCC Third Assessment Report (TAR), it was reported that volcanic and solar forcings might account for half of the temperature variations prior to 1950, but that the net effect of such natural forcings was roughly neutral since then [http://www.grida.no/climate/ipcc_tar/wg1/450.htm]. In particular, the change in climate forcing from greenhouse gases since 1750 was estimated to be 8 times larger than the change in forcing due to [[:Image:Solar Activity Proxies.png|increasing solar activity]] over the same period [http://www.grida.no/climate/ipcc_tar/wg1/251.htm#tab611]. |
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Since the TAR various studies (Lean et al., 2002, Wang et al., 2005) have suggested that irradiance changes over pre-industrial are less by a factor of 3-4 than in the reconstructions of, e.g. Hoyt and Schatten (1993), Lean (2000) used in the TAR. |
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Some work published since the IPCC TAR, has reassessed the solar contribution to the post [[1950]] warming. One paper states that ''"The best estimate of the warming from solar forcing is estimated to be 16% or 36% of greenhouse warming depending on the solar reconstruction."''.[http://climate.envsci.rutgers.edu/pdf/StottEtAl.pdf "Do Models Underestimate the Solar Contribution to Recent Climate Change" Peter A. Stott, et al, Journal of Climate, 15 DECEMBER 2003] However, this attributed solar warming is not distributed evenly, being more important towards 1950 and less important today. Since 1980 one estimate of the solar contribution is 10% to 30% ([http://www.fel.duke.edu/~scafetta/pdf/2005GL023849.pdf Scafetta and West, GRL, 2005] however a competing reconstruction of variation in solar output measured by satellite shows a negligible trend since 1980 (see [[Solar variation]]). Scafetta and West derive climate sensitivities to solar variation that are 1.5 to 3 times greater than models predict. |
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A number of studies have suggested that additional [[solar variation]] feedbacks may exist which have not been incorporated in the present models or that the relative importance of solar variation may be underestimated [http://www.dsri.dk/~hsv/SSR_Paper.pdf] [http://www.envirotruth.org/docs/Veizer-Shaviv.pdf]. Such claims are disputed (e.g. [http://stephenschneider.stanford.edu/Publications/PDF_Papers/Solar-ClimateLAUTPREPRINT.pdf] [http://www.soest.hawaii.edu/GG/FACULTY/POPP/Rahmstorf%20et%20al.%202004%20EOS.pdf]) but form an active area of current research. The outcome of this debate may play a key role in determining how much climate change is [[attribution of recent climate change|attributed to human vs. natural factors]]. |
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====Other theories==== |
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Various other hypotheses have been proposed, including but not limited to: |
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* The warming is within the range of natural variation and needs no particular explanation. |
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* The warming is a consequence of coming out of a prior cool period — the [[Little Ice Age]] — and needs no other explanation. |
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* The warming trend itself has not been clearly established, and therefore does not need any explanation. |
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At present, none of these has more than a small number of supporters within the climate science community. |
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==Climate models== |
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{{main|General circulation model}} |
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Scientists have studied this issue with computer models of the climate (see below). These models are accepted by the scientific community as being valid only after it has been shown that they do a good job of simulating known climate variations, such as the difference between summer and winter, the [[North Atlantic Oscillation]], or [[El Niño]]. All climate models that pass these tests also predict that the net effect of adding greenhouse gases will be a warmer climate in the future. The amount of predicted warming varies by model, however, which probably reflects the way different models depict clouds differently. |
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As noted above, climate models have been used by the IPCC to anticipate a warming of 1.4°C to 5.8°C between 1990 and 2100 [http://www.grida.no/climate/ipcc_tar/wg1/339.htm]. They have also been used to help determine the [[Attribution of recent climate change|causes of recent climate change]] by comparing the observed changes to those that the models predict from various natural and human derived forcing factors. |
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The most recent climate models can produce a good match to observations of global temperature changes over the last century. These models do not unambiguously attribute the warming that occurred from approximately 1910 to 1945 to either natural variation or human effects; however, they suggest that the warming since 1975 is dominated by man-made [[greenhouse gas]] emissions. Adding simulation of the ability of the environment to sink carbon dioxide suggested that rising fossil fuel emissions would decrease absorption from the atmosphere, amplifying climate warming beyond previous predictions, although ''"Globally, the amplification is small at the end of the 21st century in this model because of its low transient climate response and the near-cancellation between large regional changes in the hydrologic and ecosystem responses" ''[http://www.pnas.org/cgi/reprint/0504949102v1]. |
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Another suggested mechanism whereby a warming trend may be amplified involves the thawing of [[tundra]], which can release the potent greenhouse gas, methane, that is trapped in large quantities in [[permafrost]] and ice [[clathrates]] [http://www.newscientist.com/article.ns?id=mg18725124.500]. |
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Uncertainties in the representation of clouds are a dominant source of uncertainty in existing models, despite clear progress in modeling of clouds [http://www.grida.no/climate/ipcc_tar/wg1/271.htm]. There is also an ongoing discussion as to whether climate models are neglecting important indirect and feedback effects of [[solar variability]]. Further, all such models are limited by available computational power, so that they may overlook changes related to small scale processes and weather (e.g. storm systems, hurricanes). However, despite these and other limitations, the [[IPCC]] considers climate models "to be suitable tools to provide useful projections of future climates" [http://www.grida.no/climate/ipcc_tar/wg1/309.htm]. |
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==Issues== |
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==== The relation between global warming and ozone depletion ==== |
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{{main|Ozone depletion}} |
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Although they are often interlinked in the popular press, the connection between global warming and [[ozone depletion]] is not strong. There are four areas of linkage: |
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* Global warming from CO<SUB>2</SUB> radiative forcing is expected (perhaps somewhat surprisingly) to ''cool'' the [[stratosphere]]. This, in turn, would lead to a relative ''increase'' in ozone depletion and the frequency of ozone holes. |
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* Conversely, ozone depletion represents a radiative forcing of the climate system. There are two opposed effects: reduced ozone allows more solar radiation to penetrate, thus warming the [[troposphere]]. But a colder stratosphere emits less long-wave radiation, tending to cool the troposphere. Overall, the cooling dominates: the [[IPCC]] concludes that ''observed stratospheric [[Ozone|O<sub>3</sub>]] losses over the past two decades have caused a negative forcing of the surface-troposphere system'' [http://www.grida.no/climate/ipcc_tar/wg1/223.htm] of about –0.15 ± 0.10 W m–2 [http://www.ipcc.ch/press/SPM.pdf]. |
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* One of the strongest predictions of the GW theory is that the stratosphere should cool. However, although this is observed, it is difficult to use it for [[attribution of recent climate change|attribution]] (for example, warming induced by increased solar radiation would not have this upper cooling effect) because similar cooling is caused by ozone depletion. |
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* Ozone depleting chemicals are also greenhouse gases, representing 0.34 ± 0.03 W/m2, or about 14% of the total radiative forcing from well-mixed GHG's [http://www.ipcc.ch/press/SPM.pdf]. |
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==== The relation between global warming and global dimming ==== |
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{{main|Global dimming}} |
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Some scientists now consider that the effects of the recently recognized phenomenon of [[global dimming]] (the reduction in sunlight reaching the surface of the planet, possibly due to aerosols) may have masked some of the effect of global warming. If this is so, the indirect aerosol effect is stronger than previously believed, which would imply that the climate sensitivity to greenhouse gases is also stronger. Concerns about the effect of aerosol on the global climate were first researched as part of concerns over [[global cooling]] in the 1970s. |
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====Pre-human global warming==== |
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It is thought by some geologists that the Earth experienced global warming in the early [[Jurassic]] period, with average temperatures rising by 5 °C (9 °F). Research by the [[Open University]] published in ''Geology'' (32: 157–160, 2004 [http://www3.open.ac.uk/earth-sciences/downloads/Press%20Release.pdf]) indicates that this caused the rate of rock weathering to increase by 400%. As a result of this, carbon dioxide levels dropped back to normal over roughly the next 150,000 years. |
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Sudden release of [[methane clathrate]] (a [[greenhouse gas]]) has been hypothesized as a cause of past global warming. Two events possibly linked in this way are the [[Permian-Triassic extinction event]] and the [[Paleocene-Eocene Thermal Maximum]]. However, warming at the end of the last ice age is thought to not be due to clathrate release [http://gsa.confex.com/gsa/inqu/finalprogram/abstract_55405.htm]. |
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The greenhouse effect has also been invoked to explain how the Earth made it out of the [[Snowball Earth]] period. During this period all silicate rocks were covered by ice, thereby preventing them to combine with atmospheric carbon dioxide. The atmospheric carbon dioxide level gradually increased until it reached about 350 times current levels. At this point temperatures were raised to an average of 50 °C, hot enough to melt the ice. Increased amounts of rainfall would quickly wash the carbon dioxide out of the atmosphere. Thick layers of [[abiotic]] carbonate sediment which can be found on top the glacial rocks from this period are believed to be formed by this rapid carbon dioxide removal process. |
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Using [[paleoclimatology|paleoclimate]] data for the last 500 million years (Veizer et al. 2000, Nature 408, pp. 698-701) concluded that long-term temperature variations are only weakly coupled to CO<sub>2</sub> variations. Shaviv and Veizer (2003, [http://www.envirotruth.org/docs/Veizer-Shaviv.pdf]) extended this by arguing that the biggest long-term influence on temperature is actually the [[solar system]]'s motion around the [[Milky Way Galaxy|galaxy]]. Afterwards, they argued that over geologic time a change in CO<sub>2</sub> concentrations comparable to doubling preindustrial levels, only results in about 0.75 °C warming rather than the usual 1.5-4.5 °C reported by climate models [http://www.grida.no/climate/ipcc_tar/wg1/122.htm]. In turn Veizer's recent work has been discussed and criticised on RealClimate.org [http://www.realclimate.org/index.php?p=153]. |
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Leading palaeoclimatologist William Ruddiman has argued (eg [http://scientificamerican.com/article.cfm?chanID=sa006&colID=1&articleID=000ED75C-D366-1212-8F3983414B7F0000 Scientific American, March 2005]) that human influence on the global climate began around 8000 years ago with the development of agriculture. This prevented CO<sub>2</sub> (and later methane) levels falling as rapidly as they would have done otherwise. Ruddiman argues that without this effect, the Earth would be entering, or already have entered, a new ice age. However other work in this area ([http://www.nature.com/cgi-taf/DynaPage.taf?file=/nature/journal/v429/n6992/abs/nature02599_fs.html Nature 2004]) argues that the present interglacial is most analogous to the interglacial 400,000 years ago that lasted approximately 28,000 years, in which case there is no need to invoke the spread of agriculture for having delayed the next ice age. |
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== Public controversy == |
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{{main|Global warming controversy}} |
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Leaving the realm of scientific journals, the debate has spilled out into the public arena. In the [[United States]], some politicians have made the issue a component of their campaigns for high office. Global warming is a more central and sustained issue, however, for the [[European Union]]. |
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==Effects== |
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{{main|Effects of global warming}} |
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The predicted effects of global warming are many and various, both for the [[natural environment|environment]] and for [[civilization|human life]]. The primary effect of global warming is increasing [[carbon dioxide]] and increasing global average temperature. From this flow a variety of secondary effects, including [[sea level rise]], [[Global warming and agriculture|impacts on agriculture]], reductions in the ozone layer (see below), increased extreme weather, and the spread of disease. In some cases, the effects may already be being experienced, although it is generally difficult to attribute specific natural phenomena to long-term global warming. |
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The extent and likelihood of these consequences is a matter of considerable [[global warming controversy|controversy]]. A summary of possible effects and our current understanding can be found in the report of the [[IPCC]] Working Group II [http://www.grida.no/climate/ipcc_tar/wg2/index.htm]. |
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=== Effects on ecosystems === |
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Secondary evidence of global warming — lessened snow cover, rising sea levels, weather changes — provides examples of consequences of global warming that may influence not only human activities but also the [[ecosystem]]s. Increasing global temperature means that ecosystems may change; some [[species]] may be forced out of their habitats (possibly to extinction) because of changing conditions, while others may flourish. Few of the [[terrestrial ecoregions]] on Earth could expect to be unaffected. |
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=== Destabilisation of ocean currents === |
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''Main article: [[Effects of global warming#Destabilisation of ocean currents|Destabilisation of ocean currents]]'' |
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<!-- take summary from ref above which has had the removed "cooling trigger" section merged into it--> |
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=== Environmental refugees === |
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[[Image:Glacial lakes, Bhutan.jpg|thumb|right|250px|The termini of the glaciers in the [[Bhutan]]-[[Himalaya]]. Glacial lakes have been rapidly forming on the surface of the debris-covered glaciers in this region during the last few decades. According to [[USGS]] researchers, glaciers in the Himalaya are wasting at alarming and accelerating rates, as indicated by comparisons of satellite and historic data, and as shown by the widespread, rapid growth of lakes on the glacier surfaces. The researchers have found a strong correlation between increasing temperatures and glacier retreat.]] |
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Even a relatively small rise in sea level would make some densely settled coastal plains uninhabitable and create a significant [[refugee]] problem. If the sea level were to rise in excess of 4 metres almost every coastal city in the world would be severely affected, with the potential for major impacts on world-wide trade and economy. Presently, the IPCC predicts [[sea level rise]] of less than 1 meter through 2100, but they also warn that global warming during that time may lead to irreversible changes in the Earth's glacial system and ultimately melt enough ice to raise sea level many meters over the next millenia. It is estimated that around 200 million people could be affected by sea level rise, especially in [[Vietnam]], [[Bangladesh]], [[China]], [[India]], [[Thailand]], [[Philippines]], [[Indonesia]] and [[Egypt]]. [http://www.grida.no/climate/ipcc_tar/wg2/681.htm] [http://www.journals.royalsoc.ac.uk/app/home/contribution.asp?wasp=070d8d54cad94ca9a10ec2069c7bd079&referrer=parent&backto=issue,14,14;journal,43,114;linkingpublicationresults,1:102022,1] [http://www.actionbioscience.org/environment/chanton.html] |
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=== Spread of disease === |
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It has been claimed that global warming will probably extend the favourable zones for [[Vector_(biology)|vectors]] conveying [[infectious disease]]s such as [[malaria]]. An example of this may be the recent extension to the north [[Mediterranean]] region of [[bluetongue disease]] in [[domesticated]] [[ruminants]] associated with [[mite]] bites. Another is the increase of [[hantavirus]] infection, [[Crimean-Congo hemorrhagic fever]], [[tularemia]] and [[rabies]] in wide areas of [[Russia]] during 2004–2005 associated with a population explosion of [[rodents]] and their [[predator]]s. Some of this, however is blamed on breakdowns in governmental [[vaccination]] and rodent control programs.[http://www.promedmail.org/pls/promed/f?p=2400:1001:11691307049244640380::NO::F2400_P1001_BACK_PAGE,F2400_P1001_PUB_MAIL_ID:1010,30306] Similarly, despite the disappearance of malaria in most temperate regions, the indigenous [[mosquito]]es that transmitted it were never eliminated and remain common in some areas. Thus, although temperature is important in the transmission dynamics of malaria, many other factors are influential [http://www.cdc.gov/ncidod/eid/vol6no1/reiter.htm]. Many of these diseases or spread of diseases is started from the hyperactivity of micro organisms and their faster breeding patterns. |
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=== Financial effects === |
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Financial institutions, including the world's two largest insurance companies, Munich Re and Swiss Re, warn in a joint study ([http://www.unepfi.org/fileadmin/documents/CEO_briefing_climate_change_2002_en.pdf summary]) that "the increasing frequency of severe climatic events, coupled with social trends" could cost almost 150 billion US dollars each year in the next decade. These costs would, through increased costs related to insurance and disaster relief, burden customers, tax payers, and industry alike. |
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=== Possible positive effects === |
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[[Image:Arctic Ice Thickness.jpg|250px|right|thumb|The [[NOAA]] projects that by the [[2050s]], there will only be 54% of the volume of sea ice there was in the [[1950s]].]] |
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Global warming may also have positive effects. Plants form the basis of the biosphere. They utilize the sun's energy to convert water, nutrients, and CO<sub>2</sub> into usable [[biomass]]. Plant growth can be limited by a number of factors, including soil fertility, water, temperature, and CO<sub>2</sub> concentration. Thus, an increase in temperature and atmospheric CO<sub>2</sub> can stimulate plant growth in places where these are the limiting factors. Satellite data shows that the productivity of the northern hemisphere has indeed increased since 1982. On the other hand, an increase in the total amount of biomass produced is not necessarily all good, since [[biodiversity]] can still decrease even though a smaller number of species are flourishing. Similarly, from the human economic viewpoint, an increase in total biomass but a decrease in crop harvests would be a net disadvantage. |
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Moreover, IPCC models predict that higher CO<sub>2</sub> concentrations would only spur growth of flora up to a point, because in many regions the limiting factors are water or nutrients, not temperature or CO<sub>2</sub>. |
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Melting [[Arctic]] ice may open the [[Northwest Passage]] in summer, which would cut 5,000 [[nautical mile]]s from shipping routes between Europe and Asia. This would be of particular relevance for supertankers which are too big to fit through the [[Panama Canal]] and currently have to go around the tip of South America. According to the Canadian Ice Service, the amount of ice in Canada's eastern Arctic Archipelago decreased by 15 percent between 1969 and 2004 [http://www.washingtontimes.com/specialreport/20050612-123835-3711r.htm]. |
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==Mitigating and adapting to global warming== |
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{{main|Mitigation of global warming}} |
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"Mitigation of global warming" covers all actions aimed at reducing the extent or likelihood of global warming. The world's primary international agreement on combating climate change is the [[Kyoto Protocol]]. Various other strategies include [[Future energy development|development of new technologies]], [[nuclear power]], [[renewable energy]], [[biodiesel]], [[electric car]]s (and [[hybrid vehicle|hybrids]]), and [[fuel cell]]s, [[Energy conservation]], [[carbon tax]]es and [[carbon sequestration]] schemes. |
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Adaptation stategies accept some warming as a given and focus on preventing or reducing undesirable consequences: for example defending against [[sea level rise|rising sea levels]] or ensuring [[food security]]. |
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''See also [[Individual action against global warming]] and [[business action on climate change]].'' |
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==References== |
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* Naomi Oreskes, 2004 [http://www.sciencemag.org/cgi/content/full/306/5702/1686 Beyond the Ivory Tower: The Scientific Consensus on Climate Change] - The author discussed her survey of 928 peer-reviewed scientific abstracts on climate change. Retrieved [[December 8]], [[2004]]. Also available as a [http://www.sciencemag.org/cgi/reprint/306/5702/1686.pdf 1 page pdf file] |
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* {{Book reference |
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| Author = Ruddiman, William F. |
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| Year = 2005 |
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| Title = Plows, Plagues, and Petroleum: How Humans Took Control of Climate |
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| Publisher = New Jersey: Princeton University Press |
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| ID = ISBN 0691121648}} |
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* {{Journal reference | Title = The effect of increasing solar activity on the Sun's total and open magnetic flux during multiple cycles: Implications for solar forcing of climate | Author = Lean, J.L., Y.M. Wang, and N.R. Sheeley | Year = 2002 | Journal = Geophys. Res. Lett. | Volume = 29 | Issue = 24 | Pages = 2224| URL = http://www.agu.org/journals/gl/gl0224/2002GL015880/}}, {{DOI|10.1029/2002GL015880}} ''(online version requires registration)'' |
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* {{Journal reference |
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| Author = Wang, Y.M., J.L. Lean, and N.R. Sheeley |
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| Year = 2005 |
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| Title = Modeling the sun's magnetic field and irradiance since 1713 |
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| Journal = Astrophysical Journal |
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| Volume = 625 |
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| Pages = 522–538 |
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}} |
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* {{Journal reference |
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| Author = Hoyt, D.V., and K.H. Schatten |
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| Year = 1993 |
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| Title = A discussion of plausible solar irradiance variations, 1700-1992 |
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| Journal = J. Geophys. Res. |
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| Volume = 98 |
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| Pages = 18895–18906 |
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}} |
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==See also== |
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<!-- This section is for links to other Wikipedia pages --> |
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*[[Action on Climate Change]] |
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*[[Future energy development]] |
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*[[Global Atmosphere Watch]] |
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*[[Global cooling]] |
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*[[Global dimming]] |
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*[[Impact of global climate changes on agriculture]] |
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*[[Iris Hypothesis]] |
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*[[National Assessment on Climate Change]] |
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*[[Phenology]] |
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*[[Preventive paradigm]] |
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*[[Soft energy path]] |
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*[[United Kingdom Climate Change Programme]] |
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==External links== |
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===Data=== |
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*[http://www.cmdl.noaa.gov/ccgg/iadv/ NOAA CMDL CCGG - Interactive Atmospheric Data Visualization] NOAA CO<sub>2</sub> data |
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*[http://www.grida.no/climate/vital/13.htm UNEP - The present carbon cycle - Climate Change] carbon levels and flows |
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*[http://www.cru.uea.ac.uk/cru/data/temperature/ Temperature data] Climatic Research Unit, University of East Anglia, Norwich, UK. Philip D. Jones and other. |
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*[http://www.met-office.gov.uk/research/hadleycentre/obsdata/globaltemperature.html Hadley Centre: Global temperature data] |
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====Carbon dioxide emissions==== |
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*[http://www.eia.doe.gov/emeu/iea/res.html International Energy Annual: Reserves] |
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*[http://www.iea.org/bookshop/add.aspx?id=144 IEA Publications Bookshop - Key World Energy Statistics] |
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*[http://www.eia.doe.gov/emeu/iea/carbon.html International Energy Annual 2002: Carbon Dioxide Emissions] |
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*[http://www.eia.doe.gov/emeu/iea/Notes%20for%20Table%20H_1co2.html International Energy Annual 2002: Notes and Sources for Table H.1co2] (Metric tons of carbon dioxide can be converted to metric tons of carbon equivalent by multiplying by 12/44) |
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*[http://www.eia.doe.gov/cneaf/pubs_html/attf94_v2/appd_d.html DOE - EIA - Alternatives to Traditional Transportation Fuels 1994 - Volume 2, Greenhouse Gas Emissions] (includes "Greenhouse Gas Spectral Overlaps and Their Significance") |
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*[http://www.marshall.org/article.php?id=13 The Marshall Institute - Increasing Carbon Dioxide and Global Climate Change] - [[1 January]] [[2000]] (temp. data) |
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*[http://www.ngdc.noaa.gov/paleo/icecore/antarctica/vostok/vostok.html NOAA Paleoclimatology Program - Vostok Ice Core] |
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===Scientific=== |
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*[http://wwwghcc.msfc.nasa.gov/ghcc_home.html NASA's Global Hydrology and Climate Center] |
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*[http://www.giss.nasa.gov/research/observe/surftemp/ NASA's Goddard Institute for Space Studies] (GISS) — Global Temperature Trends. |
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*[http://www.giss.nasa.gov/research/paleo/ NASA's GISS paleoclimate site] |
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*[http://www.ucar.edu/research/climate/ National Center for Atmospheric Research] - Overview of NCAR research on climate change |
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*[http://lwf.ncdc.noaa.gov/oa/climate/globalwarming.html National Oceanic and Atmospheric Administration] — [[NOAA]], [[United States Department of Commerce]] — Global Warming FAQ |
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*[http://www.ngdc.noaa.gov/paleo/globalwarming/paleostory.html NOAA's paleoclimate site] |
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*[http://web.mit.edu/globalchange/www/ MIT Joint Program on the Science and Policy of Global Change] |
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*[http://www.lmd.jussieu.fr/pcmdi-mirror/projects/cmip/overview_ms/ms_text.html An Overview of Results from the Coupled Model Intercomparison Project (CMIP)] |
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*[http://www.acia.uaf.edu/ Arctic Climate Impact Assessment] |
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*[http://amap.no/workdocs/index.cfm?dirsub=%2FACIA%2Foverview ACIA report: Impacts of a Warming Arctic, (2004)] Arctic Climate Impact Assessment (ACIA) |
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*[http://cdiac.esd.ornl.gov/pns/faq.html Carbon Dioxide Information Analysis Centre FAQ] Includes links to lots of useful Carbon Dioxide statistics. |
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*[http://eaps.mit.edu/faculty/lindzen/cooglobwrm.pdf Some Coolness Concerning Global Warming] by [[Richard Lindzen]]. |
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*[http://www.realclimate.org RealClimate] a blog where scientists discuss the science of global warming |
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*[http://opendemocracy.com/debates/article-6-129-2488.jsp David King at openDemocracy.net] UK chief scientific advisor explains history and science of global warming |
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===Educational=== |
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*[http://www.newscientist.com/hottopics/climate/ New Scientist: Climate Change] — Latest news, articles and FAQ on climate change from New Scientist magazine. |
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*[http://www.opendemocracy.net/climate_change/index.jsp Open Democracy: Climate Change debate] — substantial article series by scientists, activists and others, and global debate about the politics of climate change. |
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*[http://www.aip.org/history/climate Discovery of Global Warming] — An extensive introduction to the topic and the history of its discovery |
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*[http://www.msc.ec.gc.ca/education/scienceofclimatechange/ Science of Climate Change] — [http://www.msc.ec.gc.ca/ Meteorological Service of Canada], a guide to understanding the science behind climate change with a thorough [http://www.msc.ec.gc.ca/education/scienceofclimatechange/understanding/FAQ/index_e.html FAQ section]. |
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*[http://www.abelard.org/briefings/global_warming.htm Global warming - a briefing document], summarising current arguments concerning global warming. They present various points of view and some of the basic problems in following the science. |
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*[http://www.nytimes.com/2005/10/25/science/earth/25arctic.html?pagewanted=print] — The Big Melt / No Escape: Thaw Gains Momentum / By ANDREW C. REVKIN / New York Times – October 25, 2005 |
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*[http://www.thewatt.com/modules.php?name=Downloads&d_op=viewdownloaddetails&lid=7&ttitle=Climate_Change_Facts_And_Impacts Climate Change: Facts and Impacts] A thorough but non jargon-filled introduction to Climate Change and it's consequences for society, the environement and the economy. |
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===Environmentalist=== |
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*[http://www.ucsusa.org/global_warming/ "Global warming is real and underway"] — [[Union of Concerned Scientists]] (UCS) |
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*[http://www.nrdc.org/globalwarming/ Natural Resources Defense Council (NRDC): overviews, news and reports on global warming] — [[NRDC]] |
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*[http://www.climatealliance.org Climate Alliance of European Cities] |
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*http://www.undoit.org Global Warming: Undo It (Environmental Defense) |
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*[http://news.bbc.co.uk/2/hi/in_depth/sci_tech/2004/climate_change/ BBC: 2004 Climate Change Feature] — Major feature from the BBC including [http://news.bbc.co.uk/1/shared/spl/hi/sci_nat/04/climate_change/html/climate.stm climate change animations], articles, Q&A, video, analysis, charts and quizes. |
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*[http://www.nwf.org/globalwarming Global Warming] — [[National Wildlife Federation]] Includes maps of impact on birds and Senate voting records. |
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*[http://zfacts.com/p/49.html Global Warming & Hurricanes] - Review based on latest articles in ''Science'' and ''Nature''. Graph of trends in 6 hurricane basins. |
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===BBC articles=== |
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*[http://news.bbc.co.uk/1/hi/sci/tech/4315968.stm BBC - Earth - melting in the heat?] |
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*[http://news.bbc.co.uk/1/hi/sci/tech/4275729.stm BBC - Greenhouse gases 'do warm oceans'] |
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*[http://news.bbc.co.uk/1/hi/sci/tech/4381960.stm BBC - Europe study shows climate risks] |
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*[http://news.bbc.co.uk/1/hi/world/americas/4400534.stm BBC - 'Gas muzzlers' challenge Bush] |
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===News clippings of events which may have been caused by global warming=== |
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* 11th Oct 2005 [http://www.nature.com/news/2005/051010/full/051010-8.html Nature News: Amazon hit by worst drought for 40 years] |
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===Global warming-skeptical=== |
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*http://www.sepp.org/ — the [[Science and Environmental Policy Project]] ([[SEPP]]) |
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*The [[George Marshall Institute]] (GMI) |
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*[http://www.john-daly.com/ John-Daly.com: Still Waiting for Greenhouse: A Lukewarm View of Global Warming] |
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*[http://www.uoguelph.ca/~rmckitri/cc.html Ross McKitrick's commented list of resources on global warming] |
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*[http://www.globalwarming.org GlobalWarming.org] |
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*[http://www.crichton-official.com/speeches/speeches_quote04.html Michael Crichton on Global Warming] |
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===Industry-sponsored=== |
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*[http://www.princeton.edu/~cmi/ — Carbon mitigation initiative] — Information on carbon capturing, storage, science and policy |
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*http://www.cei.org — the [[Competitive Enterprise Institute]]. Funded by petrol oil corporations (Source: [http://www.capitalresearch.org/search/orgdisplay.asp?Org=CEI200]) |
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*[http://www.accesstoenergy.com Access to Energy] |
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*[http://www.co2science.org CO<sub>2</sub> science magazine] |
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* The [[Greening Earth Society]] |
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*[http://www.globalwarming.org Global Warming Information Page] sponsored by the [[Cooler Heads Coalition]], a subgroup of the National Consumer Coalition. |
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*The [[Global Climate Coalition]] |
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===Independent=== |
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''Sites which are considered to be independent or receive too little support to be considered influential sponsorship'' |
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* [http://www.econlib.org/library/Enc/GreenhouseEffect.html Greenhouse Effect] by [[Thomas Schelling|Thomas C. Schelling]], winner of the 2005 Nobel Prize for economics |
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*[http://www.davidsuzuki.org/Climate_Change/ David Suzuki Foundation]— : Impacts and Solutions,on Climate Change. |
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*[http://news.bbc.co.uk/1/hi/sci/tech/3667979.stm Possible solutions] — Introduce interesting theories like "sequestering" or forcing carbon dioxide deep into the oceans |
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*[http://www.greenfacts.org/studies/climate_change/index.htm GreenFacts]— A summary of the Third Assessment Report of the IPCC |
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*[http://www.earthisland.org/eijournal/spring98/sp98a_fe.htm The PR Plot to Overheat the Earth], analysis of industry efforts to discredit global warming science, by Bob Burton and Sheldon Rampton, published in the ''Earth Island Journal''. |
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*[http://www.zmag.org/content/showarticle.cfm?SectionID=26&ItemID=4034 Sleepwalking to Extinction, by George Monbiot] ([[Z Magazine]]) |
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*[http://www.manicore.com/anglais/documentation_a/greenhouse/index.html Climate change (global warming) : a couple of answers to some elementary questions] by Jean-Marc Jancovici |
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*[http://www.brighton73.freeserve.co.uk/gw/globalwarmingfaq.htm Global Warming FAQ] by [http://www.brighton73.freeserve.co.uk/ Tom Rees] |
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*[http://www.globalissues.org/EnvIssues/GlobalWarming.asp Global Warming - a collection of articles from globalissues.org which also has developing country perspective] |
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===Other=== |
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*[http://www.brighton73.freeserve.co.uk/gw/globalwarmingfaq.htm Global Warming FAQ] — A comprehensive FAQ. |
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*[http://www.autobahn.mb.ca/~het/enviro/globalwarming.html A large compendium of links to sites with information on global warming] |
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*[http://www.istl.org/01-fall/internet.html Science and Technology Librarianship: Global Warming and Climate Change Science] — Extensive commented list of Internet resources — Science and Technology Sources on the Internet. |
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*[http://www.activistmagazine.com/index.php?option=content&task=view&id=120 Activist Magazine: Carbon Activism for Beginners] |
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*[http://www.pistehors.com/articles/global-warming.htm Global Warming and the Effects on Skiing] |
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*[http://www.abelard.org/briefings/global_warming.htm Global warming - briefing document] |
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*[http://www.environmentaldefense.org/go/paidskeptics Environmental Defence - Global Warming Skeptics: A Primer] — How ExxonMobil funds scientists and media pundits to "de-bunk" the science of climate change |
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*[http://www.svalbard-images.com/spitsbergen/global-warming-e.php Global warming - Greenpeace pictures in Spitsbergen] |
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*[http://www.pbs.org/wgbh/nova/sciencenow/3210/03.html NOVA scienceNOW] - A 7 minute video of the [[NOVA]] broadcast that aired on [[PBS]], [[July 26]], [[2005]]. Hosted by [[Robert Krulwich]], the video is about the world's fastest [[glacier]] and how "moving way too fast reveals how unpredictable the effects of global warming can be". |
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*[http://www.thewatt.com/modules.php?name=News&new_topic=20 Global Warming Related News] |
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*[http://www.energybulletin.net/3647.html]Methane Burps: Ticking Time Bomb |
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[[Category:Climatology]] |
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[[Category:Climate change| ]] |
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[[Category:History of climate]] |
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[[ca:Escalfament global]] |
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[[cs:Globální oteplování]] |
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[[da:Global opvarmning]] |
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[[de:Globale Erwärmung]] |
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[[et:Globaalne soojenemine]] |
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[[es:Calentamiento global]] |
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[[fr:Réchauffement global]] |
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[[he:התחממות גלובלית]] |
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[[it:Riscaldamento globale]] |
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[[nl:Opwarming van de aarde]] |
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[[ja:地球温暖化]] |
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[[no:Global oppvarming]] |
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[[pl:Ocieplenie klimatu]] |
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[[sv:Global uppvärmning]] |
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[[ta:புவி வெப்பநிலை அதிகரிப்பு]] |
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[[zh:全球变暖]] |
Revision as of 19:07, 16 November 2005
![](http://upload.wikimedia.org/wikipedia/commons/thumb/f/f4/Instrumental_Temperature_Record.png/250px-Instrumental_Temperature_Record.png)
![](http://upload.wikimedia.org/wikipedia/commons/thumb/8/8c/Global_Warming_Map.jpg/250px-Global_Warming_Map.jpg)
Global warming describes an increase in the average temperature of the Earth's atmosphere and oceans. The terms global warming or anthropogenic global warming are also used to describe the theory that increasing temperatures are the result of a strengthening greenhouse effect caused primarily by man-made increases in carbon dioxide and other greenhouse gases. The natural greenhouse effect keeps the Earth 30°C warmer than it otherwise would be; adding carbon dioxide to an atmosphere, with no other changes, will tend to make a planet's surface warmer; the question is, by how much?
The scientific opinion on climate change, as expressed by the UN Intergovernmental Panel on Climate Change (IPCC) and explicitly endorsed by the national science academies of the G8 nations, is that the average global temperature has risen 0.6 ± 0.2 °C since the late 19th century, and that "most of the warming observed over the last 50 years is attributable to human activities". A small minority of qualified scientists contest the view that humanity's actions have played a significant role in increasing recent temperatures. Uncertainties do exist regarding how much climate change should be expected in the future, and a hotly contested political and public debate exists over what actions, if any, should be taken in light of global warming.
Based on basic science, observational sensitivity studies, and the climate models referenced by the IPCC, temperatures may increase by 1.4 to 5.8 °C between 1990 and 2100 [1]. This is expected to result in other climate changes including rises in sea level and changes in the amount and pattern of precipitation. Such changes may increase extreme weather events such as floods, droughts, heat waves, and hurricanes, change agricultural yields, or contribute to biological extinctions. Although warming is expected to affect the frequency and magnitude of these events, it is very difficult to connect any particular event to global warming.
Overview
The scientific consensus on global warming is that the Earth is warming, and that humanity's greenhouse gas emissions are making a significant contribution. This consensus is summarized by the findings of the Intergovernmental Panel on Climate Change (IPCC). In the Third Assessment Report, the IPCC concluded that "most of the warming observed over the last 50 years is attributable to human activities". This position was recently supported by an international group of science academies from the G8 countries and Brazil, China and India [2].
Over the past century or so the global (land and sea) temperature has increased by 0.6 ± 0.2 °C [3]. The effects of global warming are increasingly visible. At the same time, atmospheric carbon dioxide has increased from around 280 parts per million (by volume) in 1800 to around 315 in 1958 and 367 in 2000, a 31% increase over 200 years. Other greenhouse gas emissions have also increased. Future CO2 levels cannot be predicted with any precision, since they depend on uncertain economic, sociological and technological developments. The IPCC SRES gives a wide range of future CO2 scenarios [4], ranging from about 0.04 to 0.1 % by volume by 2100.
Climate models, driven by estimates of increasing carbon dioxide and to a lesser extent by generally decreasing sulphate aerosols, predict that temperatures will increase (with a range of 1.4 to 5.8 °C for change between 1990 and 2100 [5]). Much of this uncertainty results from not knowing future CO2 emissions, but there is also uncertainty about the accuracy of climate models. Climate commitment studies predict that even if levels of greenhouse gases and solar activity were to remain constant, the global climate is committed to 0.5 °C of warming (some model results are as high as 1.0 °C) over the next one hundred years due to the lag in warming caused by the oceans.
Although the combination of scientific consensus and economic incentives (especially for Russia) were enough to persuade the governments of more than 150 countries to ratify the Kyoto Protocol - there are issues about just how much greenhouse gas emissions warm the planet. Uncertainties remain and have been emphasized by some politicians, and others questioning the costs needed to reduce future global warming; however, the business position on climate change is increasingly changing to accept global warming as both real and anthropogenic, and that action such as carbon emissions trading and carbon taxes is needed. The scientific consensus is questioned by a small minority of scientists.
Warming of the Earth
![](http://upload.wikimedia.org/wikipedia/commons/thumb/c/c1/2000_Year_Temperature_Comparison.png/220px-2000_Year_Temperature_Comparison.png)
Relative to 1860-1900 the global (land and sea) temperature has increased by 0.75 oC. Temperatures in the lower troposphere have increased between 0.12 and 0.22 °C per decade since 1979. Over the past 1-2 thousand years before 1850 the temperature has been relatively stable, with various (possibly local) fluctuations, such as the Medieval Warm Period or the Little Ice Age.
The period of time over which one is interested in change may vary according to the focus of the user of the term and the datasets available for investigation. Temperature record holds a discussion of the various records. An approximately global instrumental temperature record begins in about 1860; contamination from the urban heat island is believed to be small. A longer-term perspective is available from various proxy records for recent millenia; see Temperature record of the past 1000 years for a discussion of these records and their differences. Attribution of recent climate change is clearest for the most recent period (the last 50 years) for which the most detailed data is available. Satellite temperature measurements of the tropospheric temperature date from 1979.
Causes of global warming
![](http://upload.wikimedia.org/wikipedia/commons/thumb/1/1c/Carbon_Dioxide_400kyr.png/250px-Carbon_Dioxide_400kyr.png)
The climate system varies both through natural, "internal" processes as well as in response to variations in external "forcing" from both human and non-human causes, including changes in the Earth's orbit around the Sun (Milankovitch cycles), solar activity, and volcanic emissions as well as greenhouse gases. See Climate change for further discussion of these forcing processes. Climatologists accept that the earth has warmed recently. Somewhat more controversial is what may have caused this change. See attribution of recent climate change for further discussion.
Atmospheric scientists know that adding carbon dioxide (CO2) or methane (CH4) to an atmosphere, with no other changes, will tend to make a planet's surface warmer. Indeed, greenhouse gases create a natural greenhouse effect without which temperatures on Earth would be 30°C lower, and the Earth uninhabitable. It is therefore not correct to say that there is a debate between those who "believe in" and "oppose" the theory that adding CO2 or CH4 to the Earth's atmosphere will result in warmer surface temperatures on Earth, on average. Rather, the debate is about what the net effect of the addition of CO2 and CH4 will be, and whether changes in water vapor, clouds, the biosphere and various other climate factors will cancel out its warming effect. The observed warming of the Earth over the past 50 years appears to be at odds with the skeptics' theory that climate feedbacks will cancel out the warming.
Greenhouse gas emissions
![](http://upload.wikimedia.org/wikipedia/commons/thumb/b/bb/Major_greenhouse_gas_trends.png/350px-Major_greenhouse_gas_trends.png)
Coal-burning power plants, automobile exhausts, factory smokestacks, and other waste vents of the human environment contribute about 22 billion tons of carbon dioxide and other greenhouse gases into the earth's atmosphere each year. Animal agriculture, manure, natural gas, rice paddies, landfills, coal, and other sources contribute about 250 million tons of methane each year. About half of human emissions have remained in the atmosphere. The atmospheric concentrations of CO2 and CH4 have increased by 31% and 149% respectively above pre-industrial levels since 1750. This is considerably higher than at any time during the last 420,000 years, the period for which reliable data has been extracted from ice cores. From less direct geological evidence it is believed that CO2 values this high were last attained 40 million years ago. About three-quarters of the anthropogenic emissions of CO2 to the atmosphere during the past 20 years is due to fossil fuel burning. The rest is predominantly due to land-use change, especially deforestation [6].
The longest continuous instrumental measurement of CO2 mixing ratios began in 1958 at Mauna Loa. Since then, the annually averaged value has increased monotonically from 315 ppmv (see the Keeling Curve). The concentration reached 376 ppmv in 2003. South Pole records show similar growth [7]. The monthly measurements display small seasonal oscillations.
Alternative theories
Solar variation theory
![](http://upload.wikimedia.org/wikipedia/commons/thumb/0/0d/Solar-cycle-data.png/220px-Solar-cycle-data.png)
Various hypotheses have been proposed to attribute terrestrial temperature variations to variations in solar output.
In the IPCC Third Assessment Report (TAR), it was reported that volcanic and solar forcings might account for half of the temperature variations prior to 1950, but that the net effect of such natural forcings was roughly neutral since then [8]. In particular, the change in climate forcing from greenhouse gases since 1750 was estimated to be 8 times larger than the change in forcing due to increasing solar activity over the same period [9].
Since the TAR various studies (Lean et al., 2002, Wang et al., 2005) have suggested that irradiance changes over pre-industrial are less by a factor of 3-4 than in the reconstructions of, e.g. Hoyt and Schatten (1993), Lean (2000) used in the TAR.
Some work published since the IPCC TAR, has reassessed the solar contribution to the post 1950 warming. One paper states that "The best estimate of the warming from solar forcing is estimated to be 16% or 36% of greenhouse warming depending on the solar reconstruction."."Do Models Underestimate the Solar Contribution to Recent Climate Change" Peter A. Stott, et al, Journal of Climate, 15 DECEMBER 2003 However, this attributed solar warming is not distributed evenly, being more important towards 1950 and less important today. Since 1980 one estimate of the solar contribution is 10% to 30% (Scafetta and West, GRL, 2005 however a competing reconstruction of variation in solar output measured by satellite shows a negligible trend since 1980 (see Solar variation). Scafetta and West derive climate sensitivities to solar variation that are 1.5 to 3 times greater than models predict.
A number of studies have suggested that additional solar variation feedbacks may exist which have not been incorporated in the present models or that the relative importance of solar variation may be underestimated [10] [11]. Such claims are disputed (e.g. [12] [13]) but form an active area of current research. The outcome of this debate may play a key role in determining how much climate change is attributed to human vs. natural factors.
Other theories
Various other hypotheses have been proposed, including but not limited to:
- The warming is within the range of natural variation and needs no particular explanation.
- The warming is a consequence of coming out of a prior cool period — the Little Ice Age — and needs no other explanation.
- The warming trend itself has not been clearly established, and therefore does not need any explanation.
At present, none of these has more than a small number of supporters within the climate science community.
Climate models
Scientists have studied this issue with computer models of the climate (see below). These models are accepted by the scientific community as being valid only after it has been shown that they do a good job of simulating known climate variations, such as the difference between summer and winter, the North Atlantic Oscillation, or El Niño. All climate models that pass these tests also predict that the net effect of adding greenhouse gases will be a warmer climate in the future. The amount of predicted warming varies by model, however, which probably reflects the way different models depict clouds differently.
As noted above, climate models have been used by the IPCC to anticipate a warming of 1.4°C to 5.8°C between 1990 and 2100 [14]. They have also been used to help determine the causes of recent climate change by comparing the observed changes to those that the models predict from various natural and human derived forcing factors.
The most recent climate models can produce a good match to observations of global temperature changes over the last century. These models do not unambiguously attribute the warming that occurred from approximately 1910 to 1945 to either natural variation or human effects; however, they suggest that the warming since 1975 is dominated by man-made greenhouse gas emissions. Adding simulation of the ability of the environment to sink carbon dioxide suggested that rising fossil fuel emissions would decrease absorption from the atmosphere, amplifying climate warming beyond previous predictions, although "Globally, the amplification is small at the end of the 21st century in this model because of its low transient climate response and the near-cancellation between large regional changes in the hydrologic and ecosystem responses" [15].
Another suggested mechanism whereby a warming trend may be amplified involves the thawing of tundra, which can release the potent greenhouse gas, methane, that is trapped in large quantities in permafrost and ice clathrates [16].
Uncertainties in the representation of clouds are a dominant source of uncertainty in existing models, despite clear progress in modeling of clouds [17]. There is also an ongoing discussion as to whether climate models are neglecting important indirect and feedback effects of solar variability. Further, all such models are limited by available computational power, so that they may overlook changes related to small scale processes and weather (e.g. storm systems, hurricanes). However, despite these and other limitations, the IPCC considers climate models "to be suitable tools to provide useful projections of future climates" [18].
Issues
The relation between global warming and ozone depletion
Although they are often interlinked in the popular press, the connection between global warming and ozone depletion is not strong. There are four areas of linkage:
- Global warming from CO2 radiative forcing is expected (perhaps somewhat surprisingly) to cool the stratosphere. This, in turn, would lead to a relative increase in ozone depletion and the frequency of ozone holes.
- Conversely, ozone depletion represents a radiative forcing of the climate system. There are two opposed effects: reduced ozone allows more solar radiation to penetrate, thus warming the troposphere. But a colder stratosphere emits less long-wave radiation, tending to cool the troposphere. Overall, the cooling dominates: the IPCC concludes that observed stratospheric O3 losses over the past two decades have caused a negative forcing of the surface-troposphere system [19] of about –0.15 ± 0.10 W m–2 [20].
- One of the strongest predictions of the GW theory is that the stratosphere should cool. However, although this is observed, it is difficult to use it for attribution (for example, warming induced by increased solar radiation would not have this upper cooling effect) because similar cooling is caused by ozone depletion.
- Ozone depleting chemicals are also greenhouse gases, representing 0.34 ± 0.03 W/m2, or about 14% of the total radiative forcing from well-mixed GHG's [21].
The relation between global warming and global dimming
Some scientists now consider that the effects of the recently recognized phenomenon of global dimming (the reduction in sunlight reaching the surface of the planet, possibly due to aerosols) may have masked some of the effect of global warming. If this is so, the indirect aerosol effect is stronger than previously believed, which would imply that the climate sensitivity to greenhouse gases is also stronger. Concerns about the effect of aerosol on the global climate were first researched as part of concerns over global cooling in the 1970s.
Pre-human global warming
It is thought by some geologists that the Earth experienced global warming in the early Jurassic period, with average temperatures rising by 5 °C (9 °F). Research by the Open University published in Geology (32: 157–160, 2004 [22]) indicates that this caused the rate of rock weathering to increase by 400%. As a result of this, carbon dioxide levels dropped back to normal over roughly the next 150,000 years.
Sudden release of methane clathrate (a greenhouse gas) has been hypothesized as a cause of past global warming. Two events possibly linked in this way are the Permian-Triassic extinction event and the Paleocene-Eocene Thermal Maximum. However, warming at the end of the last ice age is thought to not be due to clathrate release [23].
The greenhouse effect has also been invoked to explain how the Earth made it out of the Snowball Earth period. During this period all silicate rocks were covered by ice, thereby preventing them to combine with atmospheric carbon dioxide. The atmospheric carbon dioxide level gradually increased until it reached about 350 times current levels. At this point temperatures were raised to an average of 50 °C, hot enough to melt the ice. Increased amounts of rainfall would quickly wash the carbon dioxide out of the atmosphere. Thick layers of abiotic carbonate sediment which can be found on top the glacial rocks from this period are believed to be formed by this rapid carbon dioxide removal process.
Using paleoclimate data for the last 500 million years (Veizer et al. 2000, Nature 408, pp. 698-701) concluded that long-term temperature variations are only weakly coupled to CO2 variations. Shaviv and Veizer (2003, [24]) extended this by arguing that the biggest long-term influence on temperature is actually the solar system's motion around the galaxy. Afterwards, they argued that over geologic time a change in CO2 concentrations comparable to doubling preindustrial levels, only results in about 0.75 °C warming rather than the usual 1.5-4.5 °C reported by climate models [25]. In turn Veizer's recent work has been discussed and criticised on RealClimate.org [26].
Leading palaeoclimatologist William Ruddiman has argued (eg Scientific American, March 2005) that human influence on the global climate began around 8000 years ago with the development of agriculture. This prevented CO2 (and later methane) levels falling as rapidly as they would have done otherwise. Ruddiman argues that without this effect, the Earth would be entering, or already have entered, a new ice age. However other work in this area (Nature 2004) argues that the present interglacial is most analogous to the interglacial 400,000 years ago that lasted approximately 28,000 years, in which case there is no need to invoke the spread of agriculture for having delayed the next ice age.
Public controversy
Leaving the realm of scientific journals, the debate has spilled out into the public arena. In the United States, some politicians have made the issue a component of their campaigns for high office. Global warming is a more central and sustained issue, however, for the European Union.
Effects
The predicted effects of global warming are many and various, both for the environment and for human life. The primary effect of global warming is increasing carbon dioxide and increasing global average temperature. From this flow a variety of secondary effects, including sea level rise, impacts on agriculture, reductions in the ozone layer (see below), increased extreme weather, and the spread of disease. In some cases, the effects may already be being experienced, although it is generally difficult to attribute specific natural phenomena to long-term global warming.
The extent and likelihood of these consequences is a matter of considerable controversy. A summary of possible effects and our current understanding can be found in the report of the IPCC Working Group II [27].
Effects on ecosystems
Secondary evidence of global warming — lessened snow cover, rising sea levels, weather changes — provides examples of consequences of global warming that may influence not only human activities but also the ecosystems. Increasing global temperature means that ecosystems may change; some species may be forced out of their habitats (possibly to extinction) because of changing conditions, while others may flourish. Few of the terrestrial ecoregions on Earth could expect to be unaffected.
Destabilisation of ocean currents
Main article: Destabilisation of ocean currents
Environmental refugees
![](http://upload.wikimedia.org/wikipedia/commons/thumb/c/c3/Glacial_lakes%2C_Bhutan.jpg/250px-Glacial_lakes%2C_Bhutan.jpg)
Even a relatively small rise in sea level would make some densely settled coastal plains uninhabitable and create a significant refugee problem. If the sea level were to rise in excess of 4 metres almost every coastal city in the world would be severely affected, with the potential for major impacts on world-wide trade and economy. Presently, the IPCC predicts sea level rise of less than 1 meter through 2100, but they also warn that global warming during that time may lead to irreversible changes in the Earth's glacial system and ultimately melt enough ice to raise sea level many meters over the next millenia. It is estimated that around 200 million people could be affected by sea level rise, especially in Vietnam, Bangladesh, China, India, Thailand, Philippines, Indonesia and Egypt. [28] [29] [30]
Spread of disease
It has been claimed that global warming will probably extend the favourable zones for vectors conveying infectious diseases such as malaria. An example of this may be the recent extension to the north Mediterranean region of bluetongue disease in domesticated ruminants associated with mite bites. Another is the increase of hantavirus infection, Crimean-Congo hemorrhagic fever, tularemia and rabies in wide areas of Russia during 2004–2005 associated with a population explosion of rodents and their predators. Some of this, however is blamed on breakdowns in governmental vaccination and rodent control programs.[31] Similarly, despite the disappearance of malaria in most temperate regions, the indigenous mosquitoes that transmitted it were never eliminated and remain common in some areas. Thus, although temperature is important in the transmission dynamics of malaria, many other factors are influential [32]. Many of these diseases or spread of diseases is started from the hyperactivity of micro organisms and their faster breeding patterns.
Financial effects
Financial institutions, including the world's two largest insurance companies, Munich Re and Swiss Re, warn in a joint study (summary) that "the increasing frequency of severe climatic events, coupled with social trends" could cost almost 150 billion US dollars each year in the next decade. These costs would, through increased costs related to insurance and disaster relief, burden customers, tax payers, and industry alike.
Possible positive effects
![](http://upload.wikimedia.org/wikipedia/commons/thumb/8/8a/Arctic_Ice_Thickness.jpg/250px-Arctic_Ice_Thickness.jpg)
Global warming may also have positive effects. Plants form the basis of the biosphere. They utilize the sun's energy to convert water, nutrients, and CO2 into usable biomass. Plant growth can be limited by a number of factors, including soil fertility, water, temperature, and CO2 concentration. Thus, an increase in temperature and atmospheric CO2 can stimulate plant growth in places where these are the limiting factors. Satellite data shows that the productivity of the northern hemisphere has indeed increased since 1982. On the other hand, an increase in the total amount of biomass produced is not necessarily all good, since biodiversity can still decrease even though a smaller number of species are flourishing. Similarly, from the human economic viewpoint, an increase in total biomass but a decrease in crop harvests would be a net disadvantage. Moreover, IPCC models predict that higher CO2 concentrations would only spur growth of flora up to a point, because in many regions the limiting factors are water or nutrients, not temperature or CO2.
Melting Arctic ice may open the Northwest Passage in summer, which would cut 5,000 nautical miles from shipping routes between Europe and Asia. This would be of particular relevance for supertankers which are too big to fit through the Panama Canal and currently have to go around the tip of South America. According to the Canadian Ice Service, the amount of ice in Canada's eastern Arctic Archipelago decreased by 15 percent between 1969 and 2004 [33].
Mitigating and adapting to global warming
"Mitigation of global warming" covers all actions aimed at reducing the extent or likelihood of global warming. The world's primary international agreement on combating climate change is the Kyoto Protocol. Various other strategies include development of new technologies, nuclear power, renewable energy, biodiesel, electric cars (and hybrids), and fuel cells, Energy conservation, carbon taxes and carbon sequestration schemes.
Adaptation stategies accept some warming as a given and focus on preventing or reducing undesirable consequences: for example defending against rising sea levels or ensuring food security.
See also Individual action against global warming and business action on climate change.
References
- Naomi Oreskes, 2004 Beyond the Ivory Tower: The Scientific Consensus on Climate Change - The author discussed her survey of 928 peer-reviewed scientific abstracts on climate change. Retrieved December 8, 2004. Also available as a 1 page pdf file
- . ISBN 0691121648.
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See also
- Action on Climate Change
- Future energy development
- Global Atmosphere Watch
- Global cooling
- Global dimming
- Impact of global climate changes on agriculture
- Iris Hypothesis
- National Assessment on Climate Change
- Phenology
- Preventive paradigm
- Soft energy path
- United Kingdom Climate Change Programme
External links
Data
- NOAA CMDL CCGG - Interactive Atmospheric Data Visualization NOAA CO2 data
- UNEP - The present carbon cycle - Climate Change carbon levels and flows
- Temperature data Climatic Research Unit, University of East Anglia, Norwich, UK. Philip D. Jones and other.
- Hadley Centre: Global temperature data
Carbon dioxide emissions
- International Energy Annual: Reserves
- IEA Publications Bookshop - Key World Energy Statistics
- International Energy Annual 2002: Carbon Dioxide Emissions
- International Energy Annual 2002: Notes and Sources for Table H.1co2 (Metric tons of carbon dioxide can be converted to metric tons of carbon equivalent by multiplying by 12/44)
- DOE - EIA - Alternatives to Traditional Transportation Fuels 1994 - Volume 2, Greenhouse Gas Emissions (includes "Greenhouse Gas Spectral Overlaps and Their Significance")
- The Marshall Institute - Increasing Carbon Dioxide and Global Climate Change - 1 January 2000 (temp. data)
- NOAA Paleoclimatology Program - Vostok Ice Core
Scientific
- NASA's Global Hydrology and Climate Center
- NASA's Goddard Institute for Space Studies (GISS) — Global Temperature Trends.
- NASA's GISS paleoclimate site
- National Center for Atmospheric Research - Overview of NCAR research on climate change
- National Oceanic and Atmospheric Administration — NOAA, United States Department of Commerce — Global Warming FAQ
- NOAA's paleoclimate site
- MIT Joint Program on the Science and Policy of Global Change
- An Overview of Results from the Coupled Model Intercomparison Project (CMIP)
- Arctic Climate Impact Assessment
- ACIA report: Impacts of a Warming Arctic, (2004) Arctic Climate Impact Assessment (ACIA)
- Carbon Dioxide Information Analysis Centre FAQ Includes links to lots of useful Carbon Dioxide statistics.
- Some Coolness Concerning Global Warming by Richard Lindzen.
- RealClimate a blog where scientists discuss the science of global warming
- David King at openDemocracy.net UK chief scientific advisor explains history and science of global warming
Educational
- New Scientist: Climate Change — Latest news, articles and FAQ on climate change from New Scientist magazine.
- Open Democracy: Climate Change debate — substantial article series by scientists, activists and others, and global debate about the politics of climate change.
- Discovery of Global Warming — An extensive introduction to the topic and the history of its discovery
- Science of Climate Change — Meteorological Service of Canada, a guide to understanding the science behind climate change with a thorough FAQ section.
- Global warming - a briefing document, summarising current arguments concerning global warming. They present various points of view and some of the basic problems in following the science.
- [34] — The Big Melt / No Escape: Thaw Gains Momentum / By ANDREW C. REVKIN / New York Times – October 25, 2005
- Climate Change: Facts and Impacts A thorough but non jargon-filled introduction to Climate Change and it's consequences for society, the environement and the economy.
Environmentalist
- "Global warming is real and underway" — Union of Concerned Scientists (UCS)
- Natural Resources Defense Council (NRDC): overviews, news and reports on global warming — NRDC
- Climate Alliance of European Cities
- http://www.undoit.org Global Warming: Undo It (Environmental Defense)
- BBC: 2004 Climate Change Feature — Major feature from the BBC including climate change animations, articles, Q&A, video, analysis, charts and quizes.
- Global Warming — National Wildlife Federation Includes maps of impact on birds and Senate voting records.
- Global Warming & Hurricanes - Review based on latest articles in Science and Nature. Graph of trends in 6 hurricane basins.
BBC articles
- BBC - Earth - melting in the heat?
- BBC - Greenhouse gases 'do warm oceans'
- BBC - Europe study shows climate risks
- BBC - 'Gas muzzlers' challenge Bush
News clippings of events which may have been caused by global warming
- 11th Oct 2005 Nature News: Amazon hit by worst drought for 40 years
Global warming-skeptical
- http://www.sepp.org/ — the Science and Environmental Policy Project (SEPP)
- The George Marshall Institute (GMI)
- John-Daly.com: Still Waiting for Greenhouse: A Lukewarm View of Global Warming
- Ross McKitrick's commented list of resources on global warming
- GlobalWarming.org
- Michael Crichton on Global Warming
Industry-sponsored
- — Carbon mitigation initiative — Information on carbon capturing, storage, science and policy
- http://www.cei.org — the Competitive Enterprise Institute. Funded by petrol oil corporations (Source: [35])
- Access to Energy
- CO2 science magazine
- The Greening Earth Society
- Global Warming Information Page sponsored by the Cooler Heads Coalition, a subgroup of the National Consumer Coalition.
- The Global Climate Coalition
Independent
Sites which are considered to be independent or receive too little support to be considered influential sponsorship
- Greenhouse Effect by Thomas C. Schelling, winner of the 2005 Nobel Prize for economics
- David Suzuki Foundation— : Impacts and Solutions,on Climate Change.
- Possible solutions — Introduce interesting theories like "sequestering" or forcing carbon dioxide deep into the oceans
- GreenFacts— A summary of the Third Assessment Report of the IPCC
- The PR Plot to Overheat the Earth, analysis of industry efforts to discredit global warming science, by Bob Burton and Sheldon Rampton, published in the Earth Island Journal.
- Sleepwalking to Extinction, by George Monbiot (Z Magazine)
- Climate change (global warming) : a couple of answers to some elementary questions by Jean-Marc Jancovici
- Global Warming FAQ by Tom Rees
- Global Warming - a collection of articles from globalissues.org which also has developing country perspective
Other
- Global Warming FAQ — A comprehensive FAQ.
- A large compendium of links to sites with information on global warming
- Science and Technology Librarianship: Global Warming and Climate Change Science — Extensive commented list of Internet resources — Science and Technology Sources on the Internet.
- Activist Magazine: Carbon Activism for Beginners
- Global Warming and the Effects on Skiing
- Global warming - briefing document
- Environmental Defence - Global Warming Skeptics: A Primer — How ExxonMobil funds scientists and media pundits to "de-bunk" the science of climate change
- Global warming - Greenpeace pictures in Spitsbergen
- NOVA scienceNOW - A 7 minute video of the NOVA broadcast that aired on PBS, July 26, 2005. Hosted by Robert Krulwich, the video is about the world's fastest glacier and how "moving way too fast reveals how unpredictable the effects of global warming can be".
- Global Warming Related News
- [36]Methane Burps: Ticking Time Bomb