Arctic and Antarctic Climate Change:

•     Arctic temperatures have been rising twice as rapidly as global temperatures have over the last 40 years.  In most places temperatures have risen more rapidly in winter than in summer.  In western Canada and Alaska, winter temperatures have risen 3 to 4°C in 50 years.

•      Glaciers on land have retreated in widespread fashion in these years. Alaska’s glaciers have retreated especially rapidly, and account for one-half of the loss of ice in worldwide glaciers. The area of the Greenland ice sheet that experiences summer melting has increased by 16% from 1979 to 2002, so that now an area the size of Sweden melts every summer.

•      Snow cover has declined 10% in its extent over the last 30 years.  The average annual extent of sea ice has declined by 8% over the same period, but much more in summer, by 15 to 20%.  In regions where it still exists, sea ice has become thinner by 10 to 15%.

      Sea ice is considered by many as a “key indicator” of climate change, as it is very sensitive to temperature changes both in the air above and the sea below. The authors regard sea ice as an early warning system for climate change, like the “canary in a coal mine” which warns miners of noxious gases.

3. Impacts on Vegetation

      Vegetation zones are expected to shift toward the poles, so that in the Northern Hemisphere, forests will replace much of the tundra. Tundra may move into the zone presently without vegetation.  Insect outbreaks and forest fires are expected to become more frequent and more severe. This would aid invasions by non-native species.  One beneficial effect is that agriculture may be able to expand northward because the growing season will be longer and warmer in any given place.

4. Impacts on Animals

      Species that rely on sea ice for habitat, such as polar bears, seals, walrus, and some seabirds, may be pushed closer to extinction.  Land animals, including caribou and reindeer, are likely to be stressed as their access to food sources, breeding grounds, and migration routes will be altered.  As the habitat of species shifts northward, the Arctic will see new species move in while some existing species may disappear.  A benefit is that Arctic marine fisheries, which are now very important to the region’s economy, are likely to become more productive.

5. Impact on Ultraviolet Radiation

      Greenhouse gases will cool the stratosphere to the extent that the ozone layer is not expected to recover much in the next several decades. Thus the intensity of ultraviolet (UV) radiation will remain elevated for some time to come.

      Young people in the Arctic today are expected to receive a lifetime dose of UV radiation about 30% greater than any prior generation.  Increased exposure to UV is known to cause cataracts, skin cancer, and immune system disorders.

      The extent that climate is expected to change depends greatly on two factors. The first is the level of future emissions of greenhouse gases, which is affected by societal choices and human activities well into the future.  The second factor is the extent that climate responds to future emissions.

      The Arctic Climate Impact Assessment (ACIA) chose to use just one “scenario” of future emissions of greenhouse gases, and that is the so-called B2 emissions scenario, a middle-of-the-road projection from the “Special Report on Emissions Scenarios” of the IPCC (Intergovernmental Panel on Climate Change).  The choice of one scenario made their task, and the reader’s, much easier.

      For the second factor, the ACIA chose five different climate models from various research centers to simulate future responses of the atmosphere, oceans, ice cover, and other parts of the climate “system.” In general the authors used the average prediction of these models, as well as the range of outcomes.

      “These are not worst-case or best-case scenarios, but rather fall slightly below the middle of the range of temperature rise projected by global climate models,” the ACIA Report notes.

      “Every model simulation projects significant global warming over the next 100 years,” the report adds. Even using the model that gives the least warming, and using the lowest scenario for future emissions, leads to a prediction that earth will warm twice as much over the next 100 years as it warmed in the past century.

• After 100 years, annual temperatures in the Arctic are forecast to rise by 3 – 5°C over land but as much as 7°C over the oceans. In winter, temperatures are projected to rise even more,
4 – 7°C over land and 7 – 10°C over the oceans. Arctic changes are approximately twice as great as the expected changes for the whole globe.

• Precipitation in the Arctic is expected to increase about 20% by the end of this century. Most of the increase will be in the form of rain, not snow.  Precipitation would increase much more in the Arctic than on Earth as a whole, and in all 5 climate models the variability from year-to-year is tremendous.

• Sea ice is expected to decline by 10 to 50% in addition to what has already occurred. In the summer, sea ice is expected to decrease by more than 50%, in the average of 5 models.

• The models suggest that snow cover will decrease by 10 to 20% in addition to the 10% that has been observed recently.  The decreases will be greatest in April and May, which would shorten the snow season and provoke an earlier, stronger pulse of river runoff to the Arctic Ocean.

continued. . . .

•    Rising sea level and disappearing sea ice are allowing higher waves and storm surges to erode the shoreline. Communities on the coast already are threatened by severe erosion, while others will face ever increasing risks.

•    Thawing ground will disrupt roads, pipelines, buildings, and transportation.  The shorter winter season will maker it difficult to travel on ice roads and frozen tundra, on which much transportation presently depends.

•    Indigenous peoples are facing serious threats to their way of life or even survival. Many peoples of the Arctic have always hunted whales, polar bear, seals, and caribou for food or for a livelihood. Without those animals present, their livelihood and even the basis of their cultural identity may be lost. 

Antarctic Glaciers Retreat
but only on the “Peninsula”

      Even though Antarctica as a whole has been cooling, glaciers on the Antarctic Peninsula have been retreating increasingly faster since 1950.  The peninsula is a small extension of the continent that extends northward 800 km toward South America. It is the only area of Antarctica that has experienced warming in historic times, warming about 2°C since the 1950's. A study published in Science¹ by A.J. Cook and staff of  the British Antarctic Survey documents that 87% of 244 glaciers on the Peninsula have retreated since their earliest known position (which was in 1953, on average), while the remaining 32 glaciers have advanced. The rate of retreat of the glaciers has been increasing in these years. 

      The authors inspected more than 2000 aerial photographs taken since the year 1940 and more than 100 satellite images. They discovered an abrupt transition line between a region of glacier retreat and glacier advance.  The transition line has shifted ever closer to the pole, from a position at 64°S latitude fifty years ago to about 70°S now, so that glaciers on the whole Peninsula are now retreating.

1.  “Retreating glacier fronts on the Antarctic Peninsula over the past half-century,” by A.J. Cook, A. Fox, D. Vaughan, and J. Ferrigno (2005): Science, vol. 308, p. 541–544, 22 April 2005.

River Flow into Arctic Ocean up 7%

      The land area that drains into the Arctic Ocean is much larger than the Arctic Ocean itself. That makes  this ocean sensitive to rainfall and freshwater flows from Eurasia and North America. Six large Russian rivers drain two-thirds of the water that flows from Eurasia into the Arctic.  An international team led by Bruce Peterson of Woods Hole reported¹ that observed flow in these 6 rivers increased by 7% in the 64 years ending in  1999 (most of the change was after 1966).  Using the trends of river flow and temperature, the authors projected an increase of 18 to 70% in the flow of these rivers over the next 100 years.   For comparison, an atmospheric model of NASA predicted a +35% change in river flow.

      P. Wu and colleagues simulated the historic river flows into the Arctic with the Hadley Center climate model of the United Kingdom. In their report,² all the simulations showed a strong upward trend in river flow after the 1960s.  The model gave a 6.5% increase for the 6 major river basins (Peterson had observed an increase of +7%). Wu’s team sought to attribute these change to a cause by running the Hadley model with and without human influences.  When human influence was absent, they saw no trend. With human influence present, the model predicted an increase in river flow after 1960.

      Whether or not such simulations can be believed, there is evidence that the flow of fresh water into the Arctic has increased, and may well increase further. Changes in the salinity of the North Atlantic Ocean have already been observed. Changes in the balance of fresh and salt water have the potential to slow down the overturning and mixing of the Atlantic Ocean, and ultimately, of all oceans. (See “Fair warning?”, in Climate Science Forum, Summer 2002.)

Citations:

1. “Increasing River Discharge into the Arctic Ocean,” by Bruce J. Peterson and 7 others (2002).  Science, vol. 298, p. 2171–2173, 13 Dec. 2002.

2. “Human influence on increasing Arctic river discharges,” by P. Wu, R. Wood, and P. Stott (2005). Geophysical Research Letters, vol. 32, L02703, doi 10.1029/2004GL021570, 28 Jan 2005. 

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