Climate change in Antarctica: status and future perspectives
Over the past couple decades, significant warming has been recorded over parts of Antarctica. Lack of knowledge is a fundamental obstacle to a complete understanding of climate change in Antarctica.The Siple region has been identified as one of the areas where the temperature is currently rising fastest.
Since the early 1950s, considerable warming has been measured over the Antarctic Peninsula and to some extent the rest of West Antarctica; over the same time, little change has been seen in the rest of the continent. The greatest temperature increase is seen in the western and northern parts of the Antarctic Peninsula, where the rise is 0.53°C per decade between 1951 and 2006. On the west of the Peninsula, the increase is greatest in the winter season: 1.03°C per decade in 1951-2006. In the eastern parts of the Antarctic Peninsula, temperatures have increased most in summer and autumn, rising 0.41°C per decade between 1946 and 2006. Many recent studies based on available ground measurements from research stations and automatic weather stations, as well as satellite observations, indicate that West Antarctica has also seen a temperature increase in the past few decades, calculated to about 0.1°C per decade since 1950. Sipleregionen er identifisert som ett av de områdene i verden hvor temperaturen øker raskest i dag. No statistically significant changes in surface temperature have been registered elsewhere in Antarctica.
Measurements conducted since 1957 show no statistically significant changes in total precipitation in Antarctica. However, precipitation trends vary from region to region. Increased precipitation has been registered on the west of the Antarctic Peninsula. In East Antarctica, there is as yet no conclusive evidence of an increase, but in recent years, relatively large amounts of precipitation have been observed regionally in Dronning Maud Land. It is not clear whether this can be ascribed to natural variation, or marks the beginning of a long-term increase in precipitation.
Climate over the ocean
The temperature of the Antarctic Circumpolar Current in the Southern Ocean increased by 0.17°C at 700 to 1100 metres depth between the 1950s and the 1980s. This is above the global average. The temperature increase is related to the fact that this ocean current has shifted to the south owing to a southward shift of the westerly winds in the same time span.
The bottom water that forms in Antarctica and is exported to the South Atlantic has become warmer, for reasons that remain poorly understood. The water in the Indian and Pacific sectors of the Southern Ocean has become fresher – and the same is true of the bottom water that forms here. Along the Antarctic Peninsula, remarkably strong warming has been registered in the upper water masses: over 1°C during the Antarctic summer in the period from 1995 to 1998; this is probably related to reduction of sea ice in the area..
Interpreting the observations
Studies suggest that the hole in the ozon layer above Antarctica over the past 30 years has helped limit the effects of global warming over the continent. The temperature increases on the Antarctic Peninsula are caused by warm air transported to the Peninsula with strong west winds. The increase over West Antarctica is related to higher surface temperature in the tropical part of the Pacific. Model studies show that the strong temperature increase in the Antarctic Circumpolar Current is probably due to increased emission of greenhouse gases, whereas the speed of the increase is attenuated by the cooling effect of aerosols (particles in the atmosphere). However, because of the limited amount of observational data, it is not clear how much of the rest of the warming in Antarctica can be attributed to human activities..
The information we have concerning future climate change in Antarctica is based on circulation models that consider atmosphere, ice and oceans as a whole. The models are not yet able to simulate with acceptable accuracy the changes we have already observed in Antarctica over the past couple decades, so the model results remain highly uncertain, particularly on the regional scale.
Despite the uncertainty inherent in the models, there is general agreement in the research community, based on model projections, that if the emission of greenhouse gases to the atmosphere continues at the current rate, the temperature over the Antarctic continent will increase several degrees during this century. Model projections consistently show that the surface temperature over land in Antarctica will increase through the year 2100, at a rate of between 0.14 and 0.5°C per decade. The largest increase is predicted at high altitudes inland in East Antarctica. Nonetheless, the surface temperature in 2100 is expected to remain well below the freezing point over most of Antarctica; thus the temperature increase will not contribute to melting of the Antarctic ice sheet. The models show the greatest temperature increase above sea ice in winter (0.51 ± 0.26°C per decade off the coast of East Antarctica) because of the expected retreat of sea ice, exposing the open ocean.
Climate models generally perform poorly when calculating the amount of precipitation during the 20th century owing to the difficulty of creating accurate mathematical descriptions of important processes involved in determining precipitation. Because of this, model projections into the future are also uncertain. However, most climate models predict a general increase in the intensity of the Circumpolar Current in response to an expected southward shift and intensification of the westerly winds over the Southern Ocean. The observed warming in the Southern Ocean is expected to continue, and involve all depths, although the warming in the uppermost water layers will be weaker there than in other oceans. Model calculations imply a rise in bottom water temperature of 0.25°C before 2100. This will have impact on water density and thus the circulation in the water masses.
Ongoing and expected climate changes over the next few decades influence – and will continue to influence – large-scale process with impact on the climate system within and around Antarctica. These climate changes in Antarctica will have multiple consequences. In the long run the sea ice is expected to retreat, and melting glaciers will contribute strongly to a rise in sea level. Last but not least, living conditions for plants and animals will change.
- A.J. Turner et al. 2013. Antarctic climate change and the environment: an update. Polar Record. DOI:10.1017/S0032247413000296.
- A.J. Turner et al. 2009. Antarctic climate change and the environment. Antarctic Science. DOI:10.1017/S0954102009990642.
- Jan T.M. Lenaerts et al. 2013. Recent snowfall anomalies in Dronning Maud Land, East Antarctica, in a historical and future climate perspective.Geophysical Research Letters 40 (11): 2684–2688. DOI:10.1002/grl.50559
- P.A. Mayewski et al. 2009. State of the Antarctic and Southern Ocean climate system. Reviews of Geophysics (47): 1. DOI: 10.1029/2007RG000231
- Intergovernmental Panel on Climate Change (IPCC) 2013. Fifth assessment report contribution.