It provides responses for certain topics repeatedly brought up on the talk page. Providing similar answers each time a topic is brought up uses up many editors' time and energy. The FAQ addresses these common concerns, criticisms, and arguments, and answers various misconceptions behind them.
Q2: How can you say there's a consensus when someone has compiled a long list of "skeptical" scientists?
A2: Over the years, a number of lists of so-called "skeptical scientists" have been produced. Notable among these are the Oregon Petition (circa 1999-2001, and re-circulated in 2007) and James Inhofe's list (originally released in 2007, re-released in 2008 with additional names added). These petitions have proven to be riddled with flaws To wit:
Many of the people listed aren't really scientists. For example, the definition of a "scientist" used in the Oregon Petition includes anyone who has a bachelor's degree – or anyone who claims to have a bachelor's degree, since there's no independent verification. Using this definition, approximately 25% of the US population is qualified to sign.
Some of the people listed aren't even people. Included on these lists are hoaxes ("Dr. Geri Halliwell") and companies.
Those who are scientists are listed arbitrarily, and includes people who say they aren't skeptical of global warming. The Inhofe list was compiled by Inhofe staffer Marc Morano with no effort to contact the people listed. One of those on the list, George Waldenberger, even informed Inhofe's staff that he is not skeptical of the consensus on global warming. His request to have his name removed from the list was ignored. Similarly, Steve Rayner of Oxford University has asked for his name to be removed and calls his inclusion "quite outrageous". The Heartland Institute has stated that scientists who have told the Institute that it misrepresented their views on global warming "have no right – legally or ethically – to demand that their names be removed" from the Institute's list.
Q3: Did global warming end in 1998?
A3: One of the strongest El Niño events in the instrumental record occurred during late 1997 through 1998, causing a spike in global temperature. Choosing this abnormally warm year as the starting point for comparisons with certain later years produces a cooling trend; choosing any other year in the 20th century produces a warming trend.
Scientists do not define a "trend" by looking at the difference between two given years. Instead they use methods such as linear regression that take into account all the values in a series of data. 10 years isn't long enough to detect a climate trend. The World Meteorological Organisation specifies 30 years as the standard averaging period for climate statistics so that year-to-year fluctuations are averaged out.
In a BBC interview on 13 February 2010, Phil Jones agreed that from 1995 to 2009, the global warming "trend (0.12C per decade) is positive, but not significant at the 95% significance level", though close. This has been misleadingly reported by some news sources. On 10 June 2011 Jones told the BBC that the trend over the period 1995 to 2010 had reached the 95% significance level traditionally used as a threshold by statisticians.
Q4: How can we say global warming is real when it's been so cold in such-and-such a place?
A4: This is why it is termed "global warming", not "(region X) warming". Even then, what rises is the average temperature over time - that is, the temperature will fluctuate up and down within the overall rising trend. To give an idea of the relevant time scales, the standard averaging period specified by the World Meteorological Organisation (WMO) is 30 years. Accordingly, the WMO defines climate change as "a statistically significant variation in either the mean state of the climate or in its variability, persisting for an extended period (typically decades or longer)."
Q5: Can't the increase of CO2 be from natural sources, like volcanoes or the oceans?
A5: While these claims are popular among global warming skeptics, including academically-trained ones, they are incorrect. This is known from any of several perspectives:
Current human emissions of CO2 are at least 100 times larger than volcanic emissions. Measurements of CO2 levels over the past 50 years do not show any significant rises after eruptions. This is easily seen in a graph of CO2 concentrations over the past 50 years: the strongest eruption during the period, that of Mount Pinatubo in 1991, produced no increase in the trend.
Atmospheric oxygen content is decreasing at a rate that agrees with the amount of oxygen being used to burn fossil fuels.
If the oceans were giving up some of their carbon dioxide, we would expect their carbon dioxide concentration to decrease. But instead we are measuring an increase in the oceans' carbon dioxide concentration, resulting in the oceans becoming more acidic (or more accurately, less basic).
Q6: I think the article is missing some things, or has some things wrong. Can I change it?
A6: Yes. Keep in mind that your points need to be based on documented evidence from the peer-reviewed literature, or other information that meets standards of verifiability, reliability, and no original research. If you do not have such evidence, more experienced editors may be able to help you find it (or confirm that such evidence does not exist). You are welcome to make such queries on the article's talk page but please keep in mind that the talk page is for discussing improvements to the article, not discussing the topic. There are many forums that welcome general discussions of global warming, but the article talk page is not such a forum.
Q7: Why haven't the graphs been updated?
A7: Two reasons:
There are many images used in the articles related to global warming, and there are many reasons why they may not be updated with the latest data. Some of the figures, like Global Warming Map, are static meaning that they are intended to show a particular phenomenon and are not meant to be updated frequently or at all. Others, like the Instrumental Temperature Record and Northern Hemisphere Sea Ice Extent Anomalies, use yearly data and thus are updated once per year—usually in mid- to late-January, depending upon when the data is publicly released, and when a volunteer creates the image. Still others, like Mauna Loa Carbon Dioxide, use monthly data. These are updated semi-regularly.
However, just because an image is 6 months or a year old does not mean it is useless. Robert A. Heinlein is credited with saying, "Climate is what you expect, weather is what you get," meaning that climate is defined as a long-term average of weather, usually about 30 years. This length was chosen to eliminate the year-to-year variations. Thus, in terms of climate change, any given year's data is of little import.
Q8: Isn't global warming "just a theory"?
A8: That the temperature is rising is an observation (more specifically, the summary of many observations). The explanation for this observation is a scientific theory. This is different from the common use of "theory" to mean a guess or supposition. A scientific theory is a coherent set of explanations that is compatible with the known observations, that allows predictions to be made, and that has a number of other properties (see the above linked article). A theory that makes verifiable predictions that turn out to be correct gains credibility. Strictly speaking, science does not prove anything. A theory is the best it can provide.
Q9: Does methane cause more warming than CO2?
A9: It's true that methane is more potent molecule for molecule. But there's far less of it in the atmosphere, so the total effect is smaller. The atmospheric lifetime of methane (about 10 years) is a lot shorter than that of CO2 (on the order of 100 years). So methane tracks current emissions, while CO2 accumulates in the atmosphere over long periods. For details see the greenhouse gas and global warming potential articles.
Q10: Wasn't Greenland much warmer during the period of Norse settlement?
A10: Greenland was not significantly warmer during the period of Norse settlement. While much of Greenland was and remains under a large ice shelf, the areas of Greenland that were settled by the Norse were coastal areas with fjords that, to this day, remain quite green. Please see the following images for reference:
Q11: Are the IPCC reports prepared by biased UN scientists?
A11: The IPCC reports are not produced by "UN scientists". The IPCC does not employ the scientists who generate the reports, and has no control over them. The scientists are internationally recognized experts, most with a long history of successful research in the field. They are employed by a number of different organizations, including scientific research institutes, agencies like NASA and NOAA, and universities. They receive no extra pay for their participation in the IPCC process, which is considered a normal part of their academic duties.
Q12: Hasn't global sea ice increased over the last 30 years?
A12: Measurements show that it has not. Claims that global sea ice has stayed the same or increased are a result of cherry picking two datapoints to compare, while ignoring the real (strongly statistically significant) downward trend in measurements of global sea ice.
Q13: Weren't scientists telling us in the 1970s that we were cooling instead of warming?
A13: They weren't – see the article on global cooling. An article in the Bulletin of the American Meteorological Society has reviewed the scientific literature at that time, and found that even during the 1970s the prevailing scientific concern was over warming. The common misperception that cooling was the main concern during the 1970s arose from a few studies that were sensationalized in the popular press. (Newsweek eventually apologized for having misrepresented the state of the science in the 1970s.)
Q14: Doesn't water vapor cause 98% of the greenhouse effect?
A14: Water vapour is indeed a major greenhouse gas, contributing about 36% to 70% (not 98%) of the total greenhouse effect. But water vapour has a very short atmospheric lifetime (about 10 days), compared with decades to centuries for greenhouse gases like CO2 or nitrous oxide. As a result it is very nearly in a dynamic equilibrium in the atmosphere, which globally maintains a nearly constant relative humidity. Rising temperatures caused by the long-lived greenhouse gases therefore will increase the absolute amount of water vapour in the atmosphere, amplifying the greenhouse effect. This is an example of a positive feedback. Thus, while water vapour does not act as driver of climate change, it does amplify existing trends.
Q15: Is the fact that other solar system bodies are warming evidence for a common cause (i.e. the sun)?
A15: While some solar system bodies show evidence of local or global climate change, there is no evidence for a common cause of warming.
A 2007 National Geographic article described the views of Khabibullo Abdusamatov, who claims that the sun is responsible for global warming on both Earth and Mars. Abdussamatov's views have no support in the scientific community, as the second page of the National Geographic article makes clear: "His views are completely at odds with the mainstream scientific opinion" said Colin Wilson, a planetary physicist at England's Oxford University. [...] Amato Evan, a climate scientist at the University of Wisconsin, Madison, added that "the idea just isn't supported by the theory or by the observations."
There is no reliable source claiming that Jupiter is warming. However, observations of the Red Spot Jr. storm suggest Jupiter could be in a period of global climate change. This is hypothesized to be part of an approximately 70 year global climate cycle, characterized by the relatively rapid forming and subsequent slow erosion and merging of cyclonic and anticyclonic vortices that help transfer heat between Jupiter's poles and equator. The cycle works like this: As the vortices erode, heat exchange is reduced; this makes the poles cool down and the equatorial region heat up; the resulting temperature difference destabilizes the atmosphere, leading to the creation of new vortices.
Pluto has an extremely elliptical orbit with a period of about 248 years. Data are sparse, but two data points from 1988 and 2002 indirectly suggest that Pluto warmed between those two dates. Pluto's temperature is heavily influenced by its elliptical orbit - it was closest to the sun in 1989 and has slowly receded since. Because of thermal inertia, it is expected to warm for a while after it passes perihelion (similar to how our warmest summer temperatures occur a month or two after the longest day of the year). No other mechanism has so far been seriously suggested. Here is a reasonable summary, and this paper discusses how the thermal inertia is provided by sublimation and evaporation of parts of Pluto's atmosphere. A more popular account is here and in Wikipedia's own article.
Q19: Is an increase in global temperature of, say, 6 degrees Fahrenheit (3.3 degrees Celsius) important?
A19: The nearest concept that is relevant is that there are ranges to which species and human society have adapted. Though it may not sound like much, a global temperature rise of 6 degrees Fahrenheit (3.3 degrees Celsius) is huge in climate terms. For example, the sea level rise it produced would flood coastal cities around the world.
Earth climate has varied significantly over geological ages. The question of an "optimal temperature" makes no sense without a clear optimality criterion. Over geological time spans, ecosystems adapt to climate variations. But global climate variations during the development of human civilization (i.e., the past 12,000 years) have been remarkably small. Human civilization is highly adapted to the current stable climate. Agricultural production depends on the proper combination of soil, climate, methods, and seeds. Most large cities are located on the coast, and any significant change in sea level would strongly affect them. Migration of humans and ecosystems is limited by political borders and existing land use. In short, the main problem is not the absolute temperature, but the massive and unprecedentedly fast change in climate, and the second order-effects to human societies. The IPCC AR4 WG2 report has a detailed discussion of the effects of rapid climate change.
Q20: Why are certain proposals discarded, deleted, or ignored? Who is Scibaby?
A20:Scibaby is a long term abusivesock-master (or coordinated group of sock masters) who has created 984 confirmed sock puppets, another 218 suspected socks, and probably many untagged or unrecognized ones. This page lists some recent creations. His modus operandi has changed over time, but includes proposing reasonably worded additions on the talk page that only on close examination, turn out to be irrelevant, misinterpreted, or give undue weight to certain aspects, apparently with the aim of wasting time and/or appearing as the innocent victim of Wikipedia's alleged AGW cabal. Scibaby is banned, and Scibaby socks are blocked as soon as they are identified. Some editors silently revert his additions, per WP:DENY, while others still assume good faith even for likely socks and engage them.
Q21: What about this really interesting recent peer reviewed paper I read or read about, that says...?
A21: There are many peer-reviewed papers published every month in scientific journals such as Geophysical Research Letters, the Journal of Climate and others. We can't include all of them, but the article does include references to individual papers where there is consensus that they best represent the state of climatology. This is in accordance with the "due weight" principle (WP:WEIGHT) of the Neutral point of view policy and the "Wikipedia is not an indiscriminate collection of information" principle (WP:INFO) of the What Wikipedia is not policy.
Q22: Why does the article define "global warming" as a recent phenomenon? Hasn't the planet warmed and cooled before?
A22: Yes, the planet has warmed and cooled before. However, the term "global warming" has lost most of its generic meaning and is used nearly exclusively to refer to the recent episode, often even directly connected with the greenhouse effect. See e.g. Meriam-Webster, Encarta, OED. Similarly, "global warming" is used nearly exclusively to refer to the current episode in the academic literature.. Per WP:COMMONNAME, we use the term in this most common meaning. Climate change deals with the more general concept.
Q23: Did the CERN CLOUD experiment prove that global warming is caused not by human activity but by cosmic rays?
A23: No. For cosmic rays to be causing global warming, all of the following would have to be true, whereas only the italicized one was tested in the 2011 experiment:
Solar magnetic field must be getting stronger
The number of cosmic rays reaching Earth must be dropping
Cosmic rays must successfully seed clouds, which requires:
Cosmic rays must trigger aerosol (liquid droplet) formation,
These newly-formed aerosols must grow sufficiently through condensation to form cloud-condensation nuclei (CCN),
The CCN must lead to increased cloud formation, and
Cloud cover on Earth must be declining.
Perhaps the study's lead author, Jasper Kirkby, put it best: "...it [the experiment] actually says nothing about a possible cosmic-ray effect on clouds and climate, but it's a very important first step."
^J. L. Elliot, A. Ates, B. A. Babcock, A. S. Bosh, M. W. Buie, K. B. Clancy, E. W. Dunham, S. S. Eikenberry, D. T. Hall, S. D. Kern, S. K. Leggett, S. E. Levine, D.-S. Moon, C. B. Olkin, D. J. Osip, J. M. Pasachoff, B. E. Penprase, M. J. Person, S. Qu, J. T. Rayner, L. C. Roberts, Jr, C. V. Salyk, S. P. Souza, R. C. Stone, B. W. Taylor, D. J. Tholen, J. E. Thomas-Osip, D. R. Ticehurst and L. H. Wasserman (10 July 2003). "The recent expansion of Pluto's atmosphere". Nature (424): 165–168. doi:10.1038/nature01762.