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{{doi|10.1002/grl.50316}} predicts an ice-free summertime Arctic as early as by 2020. April 12, 2013 USA Today.com/story/tech/sciencefair/2013/04/12/arctic-summer-ice/2077579/
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A 2010 study attributes that the recent Arctic temperature amplification was caused by the loss of sea ice itself, which exposes water instead of more reflective ice to solar radiation.<ref name="nature09051"/>
A 2010 study attributes that the recent Arctic temperature amplification was caused by the loss of sea ice itself, which exposes water instead of more reflective ice to solar radiation.<ref name="nature09051"/>

A study published in 2013 shows simply extending summertime ice melting trends into the future in a straight line predicts an ice-free summertime Arctic as early as by 2020.<ref>{{doi|10.1002/grl.50316}}</ref><ref>[http://www.usatoday.com/story/tech/sciencefair/2013/04/12/arctic-summer-ice/2077579/ ''Arctic summers may be ice free sooner than predicted''] April 12, 2013 [[USA Today]]</ref>


==Effects==
==Effects==

Revision as of 00:37, 22 April 2013

The image above shows where average air temperatures (October 2010–September 2011) were up to 3 degrees Celsius above (red) or below (blue) the long-term average (1981–2010).
The maps above compare the Arctic ice minimum extents from 2012 (top) and 1984 (bottom). In 1984 the sea ice extent was roughly the average of the minimum from 1979 to 2000, and so was a typical year. The minimum sea ice extent in 2012 was roughly half of that average.

Ongoing changes in the climate of the Arctic include rising temperatures, loss of sea ice, and melting of the Greenland ice sheet.[1][2][3] The Arctic ocean will likely be free of summer sea ice before the year 2100. Projections as to when precisely this will occur vary between the years 2060–2080,[4] 2030,[5][6] and 2016.[7][8] Because of the amplified response of the Arctic to global warming, it is often seen as a high-sensitivity indicator of climate change. Scientists also point to the potential for release of methane from the Arctic region, especially through the thawing of permafrost and methane clathrates. Arctic climate changes are summarized in the IPCC Fourth Assessment Report and the Arctic Climate Impact Assessment.

The National Oceanic and Atmospheric Administration (NOAA)'s Arctic Report Card presents annually updated, peer-reviewed information on recent observations of environmental conditions in the Arctic relative to historical records.

Modelling, history, and predictions of sea ice

See also: Arctic sea ice ecology and history

Computer models predict that the sea ice area will continue to shrink in the future, although recent work has called into question their ability to accurately predict sea ice changes.[9] Current climate models frequently underestimate the rate of sea ice retreat.[10] In 2007 the IPCC reported that "the projected reduction [in global sea ice cover] is accelerated in the Arctic, where some models project summer sea ice cover to disappear entirely in the high-emission A2 scenario in the latter part of the 21st century.″ [11] There is currently no scientific evidence that a seasonally ice-free Arctic Ocean existed anytime in the last 700,000 years, although there were periods when the Arctic was warmer than it is today.[12][13] Scientists are studying possible causal factors such as direct changes resulting from the greenhouse effect as well as indirect changes such as unusual wind patterns,[14] rising Arctic temperatures,[15] or shifting water circulation[16] (such as increasing inflows of warm, fresh water to the Arctic Ocean from rivers.)

Sea ice coverage in 1980 (bottom) and 2012 (top), as observed by passive microwave sensors on NASA’s Nimbus-7 satellite and by the Special Sensor Microwave Imager/Sounder (SSMIS) from the Defense Meteorological Satellite Program (DMSP). Multi-year ice is shown in bright white, while average sea ice cover is shown in light blue to milky white. The data shows the ice cover for the period of 1 November through 31 January in their respective years.

According to the Intergovernmental Panel on Climate Change, "warming in the Arctic, as indicated by daily maximum and minimum temperatures, has been as great as in any other part of the world."[17] Reduction of the area of Arctic sea ice means less solar energy is reflected back into space, thus accelerating the reduction.[18] Studies have shown that recent warming in the polar regions was due to the net effect human influence; the warming radiative forcing of greenhouse gases is only partially offset by the cooling effect of ozone depletion.[19] Reliable measurement of sea ice edge begin within the satellite era in the late 1970s. Before this the region was less well monitored by a combination of ships, buoys and aircraft.[20] On top of the long-term negative trend in recent years, attributed to global warming, there is considerable interannual variation.[21] Some of this variation may be related to effects such as the arctic oscillation, which may itself be related to global warming;[22] some of the variation is essentially random "weather noise".

The Arctic sea ice September minimum extent reached new record lows in 2002, 2005, 2007 (39.2 percent below the 1979–2000 average) and 2012. (Roughly 50% below the 1979-2000 average)[23] In 2007, Arctic sea ice broke all previous records by early August—a month before the end of melt season, with the biggest decline ever in Arctic sea ice minimum extent, more than a million square kilometers.[24] In the first time in human memory, the fabled Northwest Passage opened completely.[25] The dramatic 2007 melting surprised and concerned scientists.[26][27]

Seasonal variation and long term decrease of Arctic sea ice volume as determined by measurement backed numerical modelling.[28]
1870–2009 Northern hemisphere sea ice extent in million square kilometers. Blue shading indicates the pre-satellite era; data then is less reliable. In particular, the near-constant level extent in Autumn up to 1940 reflects lack of data rather than a real lack of variation.

From 2008 to 2011, Arctic sea ice minimum extent was higher than 2007, but it did not return to the levels of previous years.[29][30] In 2012 however, the 2007 record low was exceeded in late August with 3 weeks still left in the melt season.[31] A few days later, as August ended, the sea ice extent dropped below 4 million square kilometers for the very first time on record.[32] It continued to fall, going below 3 and half million square kilometers by mid September, over 600,000 square kilometers lower than the 2007 record low.[33][34] It bottomed out on 16 September 2012 at 3.41 million square kilometers (1.32 million square miles), or 760,000 square kilometers (293,000 square miles) below the previous low set on 18 September 2007.[32]

The sea ice thickness field, and accordingly the ice volume and mass, is much more difficult to determine than the extension. Exact measurements can be made only at a limited number of points. Because of large variations in ice and snow thickness and consistency air- and spaceborne-measurements have to be evaluated carefully. Nevertheless the studies made support the assumption of a dramatic decline in ice age and thickness.[30] The Catlin Arctic Survey reported an average thickness of 1.8 meters across the northern Beaufort Sea, an area that had traditionally contained older, thicker ice.[35] Another approach[28] is to simulate ice growth, melting and drift numerically in an integrated ocean-atmosphere model with input parameters fine tuned to fit model output to known thickness and extent data.

The rate of the decline in entire arctic ice coverage is accelerating. From 1979–1996, the average per decade decline in entire ice coverage was a 2.2% decline in ice extent (i.e., area with at least 15% sea ice coverage) and a 3% decline in ice area. For the decade ending 2008, these values have risen to 10.1% and 10.7%, respectively. These are comparable to the September to September loss rates in year-round ice (i.e., perennial ice, which survives throughout the year), which averaged a retreat of 10.2% and 11.4% per decade, respectively, for the period 1979–2007.[36] This is consistent with ICESat measurements indicating decreased thickness in arctic ice and a decline in multi-year ice. For the period 2005–2008, multi-year ice decreased 42% in coverage and 40% in volume, a loss of ~6300 km3.[37] While the arctic ice coverage showed an accelerating downward trend, recent reports on the arctic ice volume showed an even sharper decline then the ice coverage. Since 1979, the ice volume has shrunk by 80% and in just the past decade the volume declined by 36% in the autumn and 9% in the winter.[38]

A 2010 study attributes that the recent Arctic temperature amplification was caused by the loss of sea ice itself, which exposes water instead of more reflective ice to solar radiation.[39]

A study published in 2013 shows simply extending summertime ice melting trends into the future in a straight line predicts an ice-free summertime Arctic as early as by 2020.[40][41]

Effects

Earlier retreat of sea ice in Barrow, Alaska

The effects of Arctic climate change include a marked decrease in Arctic sea ice; thawing permafrost, leading to the release of methane, a potent greenhouse gas;[42] the release of methane from clathrates, leading to longer time-scale methane release;[43] the observed increase in melt on the Greenland Ice Sheet in recent years; and potential changes in patterns of ocean circulation. Scientists worry that some of these effects may cause positive feedbacks which could accelerate the rate of global warming.

Sea ice

The number of days where the arctic is in the melt stage has increased since satellite records began in 1979. Red indicates more melting, blue less melting.

The sea ice in the Arctic region is in itself important in maintaining global climate due to its albedo (reflectivity).[44] Melting of this sea ice will therefore exacerbate global warming due to positive feedback effects, where warming creates more warming by increased solar absorption.[44][45] An important feedback in the Arctic currently is ice-albedo feedback. The loss of the Arctic sea ice may represent a tipping point in global warming, when 'runaway' climate change starts.[46][47] This would be due to the release of methane from permafrost and clathrates in the region, and also because of ice-albedo feedback effects. However, recent research has challenged the notion of ice-albedo feedback causing an imminent Arctic sea ice tipping point.[48][49] Other scientists though believe that the Arctic has already passed the tipping point. Professor Peter Wadhams told the Guardian in September 2012 after the Arctic sea ice extent hit a record low that he predicts the Arctic will be ice free within the next four years.[50]

The reduction of sea ice has also boosted the productivity of phytoplankton by about twenty percent over the past thirty years. However, the effect on marine ecosystems is unclear, since the larger types of phytoplankton, which are the preferred food source of most marine animals, do not appear to have increased as much as the smaller types. So far, arctic phytoplankton have not had a significant impact on the global carbon cycle.[51] In summer, the melt ponds on young and thin ice have allowed sunlight to penetrate the ice, in turn allowing phytoplankton to bloom in unexpected concentrations, although it is unknown just how long this phenomenon has been occurring.[52]

Projected change in polar bear habitat from 2001–2010 to 2041–2050

3 April 2007, the National Wildlife Federation urged the United States Congress to place polar bears under the Endangered Species Act.[53] Four months later, the United States Geological Survey completed a year-long study[54] which concluded in part that the floating Arctic sea ice will continue its rapid shrinkage over the next 50 years, consequently wiping out much of the polar bear habitat. The bears would disappear from Alaska, but would continue to exist in the Canadian Arctic Archipelago and areas off the northern Greenland coast.[55] Secondary ecological effects are also resultant from the shrinkage of sea ice; for example, Polar Bears are denied their historic length of seal hunting season due to late formation and early thaw of pack ice.

Loss of permafrost

Main article: Arctic methane release

Sea ice loss has melting effects on permafrost,[56] both in the sea,[57] and on land[58] and consequential effects on methane release, and wildlife.[58] Some studies imply a direct link, as they predict cold air passing over ice is replaced by warm air passing over the sea. This warm air carries heat to the permafrost around the Arctic, and melts it.[58] This thawing of the permafrost might accelerate methane release from areas like Siberia.[59] When the temperature warms sufficiently to cause the deep layers of ice underground (the permafrost) to melt, ground water will start seeping into the underlying strata and aquifer and thereby reduce the level of moisture. It may also become farmland after it is drained by canals as was done in the northern American Midwest region so wheat and corn could be farmed in what was previously swampland.[60]

Changes in vegetation

Western Hemisphere Arctic Vegetation Index Trend
Eastern Hemisphere Vegetation Index Trend

Over the past three decades, temperatures have risen faster in the Arctic than anywhere else in the world. Consequently, the growing season has gotten longer in the far northern latitudes, bringing major changes to plant communities in tundra and boreal (also known as taiga) ecosystems.

For decades, instruments on various NASA and NOAA satellites have continuously monitored vegetation from space. The Moderate Resolution Imaging Spectroradiometer (MODIS) and Advanced Very High Resolution Radiometer (AVHRR) instruments measure the intensity of visible and near-infrared light reflecting off of plant leaves. Scientists use that information to calculate the Normalized Difference Vegetation Index (NDVI), an indicator of photosynthetic activity or “greenness” of the landscape.

The maps above show NDVI trends between July 1982 and December 2011 for the northern portions of North America and Eurasia. Shades of green depict areas where plant productivity and abundance increased; shades of brown show where photosynthetic activity declined. There was no significant trend in areas that are white, and areas that are gray were not included in the study. An international team of university and NASA scientists published their analysis of the NDVI data in Nature Climate Change in March 2013.

The maps show a ring of greening in the treeless tundra ecosystems of the circumpolar Arctic—the northernmost parts of Canada, Russia, and Scandinavia. Tall shrubs and trees started to grow in areas that were previously dominated by tundra grasses. The researchers concluded that plant growth had increased by 7 to 10 percent overall.

However, boreal forests, particularly those in North America, showed a different response to warming. Many boreal forests greened, but the trend was not as strong as it was for tundra of the circumpolar Arctic. In North America, some boreal forests actually experienced “browning” (less photosynthetic activity) over the study period. Droughts, forest fire activity, animal and insect behavior, industrial pollution, and a number of other factors may have contributed to the browning.

“Satellite data identify areas in the boreal zone that are warmer and drier and other areas that are warmer and wetter,” explained co-author Ramakrishna Nemani of NASA’s Ames Research Center. “Only the warmer and wetter areas support more growth.”

“We found more plant growth in the boreal zone from 1982 to 1992 than from 1992 to 2011, because water limitations were encountered in the later two decades of our study,” added co-author Sangram Ganguly of the Bay Area Environmental Research Institute and NASA Ames. [61]

The less severe winters in tundra areas allow shrubs such as alders to replace moss and lichens. The feedback effect of shrubs on the tundra's permafrost is unclear, however. In the winter they trap more snow which insulates the permafrost from extreme cold spells, but in the summer they shade the ground from direct sunlight.[62]

Clathrate gun

Main article: Clathrate gun hypothesis

Sea ice serves to stabilise methane deposits on and near the shoreline,[63] preventing the clathrate breaking down and outgassing methane into the atmosphere. Any methane released to the atmosphere will then cause further warming.[42]

Melting of the Greenland Ice Sheet

Albedo Change on Greenland
Greenland Ice Sheet Mass Trend [when?]

Models predict a sea-level contribution of about 5 centimetres (2 in) from melting in Greenland during the 21st century.[64] It is also predicted that Greenland will become warm enough by 2100 to begin an almost complete melt during the next 1,000 years or more.[65][66] In early July 2012, 97% percent of the Ice Sheet experienced some form of surface melt including the summits.[67]

Ice thickness measurements from the GRACE satellite indicate that ice mass loss is accelerating. For the period 2002–2009, the rate of loss increased from −137 Gt/yr to −286 Gt/yr, with an acceleration of −30 gigatonnes per year per year.[68]

Effect on ocean circulation

See also: Shutdown of thermohaline circulation and Ocean anoxic event

Although this is now thought unlikely in the near future, it has also been suggested that there could be a shutdown of thermohaline circulation, similar to that which is believed to have driven the Younger Dryas, an abrupt climate change event. There is also potentially a possibility of a more general disruption of ocean circulation, which may lead to an ocean anoxic event, although these are believed to be much more common in the distant past. It is unclear whether the appropriate pre-conditions for such an event exist today.

Control of Arctic climate change

Geoengineering

See also: Arctic geoengineering and Geoengineering

Geoengineering approaches offer interventions which may increase Arctic ice, or reduce its decline.[69] These operate either by regional effects (Arctic geoengineering) or global effects (geoengineering). Several specific Arctic geoengineering schemes have been proposed to reduce Arctic climate change. Further, scientists such as Paul Crutzen have argued for general geoengineering proposals such as using stratospheric sulfur aerosols to be used, which will affect the Arctic if deployed in or near this region.

According to John Holdren, Assistant to the President of the United States for Science and Technology, complete loss of summer sea ice in the Arctic would be a milestone that could justify geoengineering in order to purposely cool the climate. Holdren believes that complete loss of summer sea ice in the Arctic could signal an increased chance of "really intolerable consequences."[70]

Research

National

Individual countries within the Arctic zone, Canada, Denmark (Greenland), Finland, Iceland, Norway, Russia, Sweden, and the United States (Alaska) conduct independent research through a variety of organizations and agencies, public and private, such as Russia's Arctic and Antarctic Research Institute. Countries who do not have Arctic claims, but are close neighbors, conduct Arctic research as well, such as the Chinese Arctic and Antarctic Administration (CAA).

International

International cooperative research between nations has become increasingly important:

Territorial claims

Main article: Territorial claims in the Arctic

Growing evidence that global warming is shrinking polar ice has added to the urgency of several nations' Arctic territorial claims in hopes of establishing resource development and new shipping lanes, in addition to protecting sovereign rights.[74]

Danish Foreign Minister Per Stig Møller and Greenland's Premier Hans Enoksen invited foreign ministers from Canada, Norway, Russia and the United States to Ilulissat, Greenland for a summit in May 2008 to discuss how to divide borders in the changing Arctic region, and a discussion on more cooperation against climate change affecting the Arctic.[75] At the Arctic Ocean Conference, Foreign Ministers and other officials representing the five countries announced the Ilulissat Declaration on 28 May 2008.[76][77]

Social Impacts

Many of the causes of climate change in the Arctic can be attributed to the effect that humans have had on the atmosphere, greenhouse effect is mainly caused by the increase in CO2 levels created by people.[78] Climate change is having a direct impact on the people that live in the Arctic, as well as other societies around the world.[79] People are affecting the geographic space of the Arctic and the Arctic is affecting people.

The warming environment presents challenges to local communities such as the Inuit. Hunting, which is a major way of survival for some small communities, will be changed with increasing temperatures.[80] The reduction of sea ice will cause certain species populations to decline or even become extinct.[79] In good years, some communities are fully employed by the commercial harvest of certain animals.[80] The harvest of different animals fluctuates each year and with the rise of temperatures it is likely to continue changing and creating issues for Inuit hunters. Unsuspected changes in river and snow conditions will cause herds of animals, including reindeer, to change migration patterns, calving grounds, and forage availability.[79]

Governments and business entrepreneurs are attempting to benefit from the melting sea ice.[81] Major shipping lanes are opening up, the northern sea route route had 34 passages in 2011 while the Northwest Passage had 22 traverses, this is more than ever in history.[82] These sea routes could see a lot of economic benefits for those involved.[82] Shipping companies are likely to benefit from the shortened distance of these northern routes. Access to natural resources will increase, including valuable minerals and offshore oil and gas.[79] This will likely bring new interestest to those directly involved. At first, it is likely that finding and controlling these resources will be difficult with the continual moving ice.[79] Expansion of tourism is probable in the arctic as sea ice reduces. With less ice, exploration and sight seeing in the Arctic will become continuously safer and popular.[79]

Transportation in the Arctic is already beginning to struggle. Some transportation routes and pipelines on land are being disrupted by the melting of ice.[79] Many Arctic communities rely on frozen roadways to transport supplies and travel from area to area.[79] The changing landscape and unpredictability of weather is creating challenges that were non-existent previously in the Arctic.[83] The adaptation to the continual changing in the environment will be a challenge. The relationship between people, communities, and institutions is important when trying to understand adaptations processes.[83]

See also

References

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Further reading

External links

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