User:StephenHudson/AntkClimCh

Climate change

Antarctic Skin Temperature Trends between 1981 and 2007, based on thermal infrared observations made by a series of NOAA satellite sensors. Skin temperature trends do not necessarily reflect air temperature trends.

The temperature record for Antarctica goes back only to 1950s, and consists of sparse network of stations, only some of which have a long, continuous period of observation. Most of the records that are available are from the Antarctic Peninsula or other coastal regions. In the entire interior of the continent, which is larger than Europe or the United States, there are only two stations (South Pole and Vostok) with decades-long periods of weather observations. In recent years automatic weather stations and meteorological satellites have started to help fill in the data gaps, but the temperatures derived from these may not be as reliable and their period of record is limited. These limitations have made it difficult to be certain about what, if any, long-term trends may be happening in Antarctica.

Climate models predict that, during this century, increasing greenhouse gas concentrations will cause temperatures in Antarctica to increase more than the global mean temperature, but less than those in the Arctic. There has been a clear and significant warming on the Antarctic Peninsula over the last 50 years. By contrast, studies published since 2002 looking at continent-wide temperature trends have produced less clear-cut results. All of these studies report some cooling in Antarctica, and only one of them reports finding the overall

The continent-wide average surface temperature trend of Antarctica is positive and significant at >0.05°C/decade since 1957. The West Antarctic ice sheet has warmed by more than 0.1°C/decade in the last 50 years, and is strongest in winter and spring. Although this is partly offset by fall cooling in East Antarctica, this effect is restricted to the 1980s and 1990s.

The British Antarctic Survey, which has undertaken the majority of Britain's scientific research in the area, has the following positions: [1]

• Ice makes polar climate sensitive by introducing a strong positive feedback loop.
• Melting of continental Antarctic ice could contribute to global sea level rise.
• Climate models predict more snowfall than ice melting during the next 50 years, but models are not good enough for them to be confident about the prediction.
• Antarctica seems to be both warming around the edges and cooling at the center at the same time. Thus it is not possible to say whether it is warming or cooling overall.
• There is no evidence for a decline in overall Antarctic sea ice extent.
• The central and southern parts of the west coast of the Antarctic Peninsula have warmed by nearly 3°C. The cause is not known.
• Changes have occurred in the upper atmosphere over Antarctica.

NASA map showing snowmelt in areas where it never melted before

The area of strongest cooling appears at the South Pole, and the region of strongest warming lies along the Antarctic Peninsula. A possible explanation is that loss of UV-absorbing ozone may have cooled the stratosphere and strengthened the polar vortex, a pattern of spinning winds around the South Pole. The vortex acts like an atmospheric barrier, preventing warmer, coastal air from moving in to the continent's interior. A stronger polar vortex might explain the cooling trend in the interior of Antarctica. [2]

In their latest study (September 20, 2007) NASA researchers have confirmed that Antarctic snow is melting farther inland from the coast over time, melting at higher altitudes than ever and increasingly melting on Antarctica's largest ice shelf.

There is also evidence for widespread glacier retreat around the Antarctic Peninsula.

Climate change

Temperature record for Antarctica goes back to 1950s, and consists of sparse station network with few stations with long history. Antarctica as a continent is somewhat specific in its recent temperature history. Although climate models predict greater rate of warming in polar regions than globally, Antarctica has not warmed at all in previous couple of decades. At least four comprehensive studies were conducted in recent years, collecting temperature data over Antarctica for period since 1950s until 2000s. All of them have found slight warming in earliest portion of the record (circa 1957-1965). Since mid 1960s, all major studies detect cooling over the most of Antarctica. Only place that all the time exhibits strong warming is Antarctic Peninsula, which amounts to 0.5% of Antarctica land mass.

Doran et al (2002) paper published in journal Nature found overall cooling over Antarctica. Their study finds “a net cooling on the Antarctic continent between 1966 and 2000, particularly during summer and autumn.”

Chapman and Walsh, (2007) in the paper published by Journal of Climate collected temperature in and around Antarctica from 460 locations including 19 manned surface observation stations located on the continent, 73 automated weather stations, and the 2° latitude by 2° longitude gridded sea surface temperature time series. They found little change in temperature over Antarctica in last 50 years (apart from Peninsula). From the beginning of record until about 1965 they find slight warming, since 1965 slight cooling: ““Trends computed using these analyses show considerable sensitivity to start and end dates with starting dates before 1965 producing overall warming and starting dates from 1966 to 1982 producing net cooling rates over the region.”

Monaghan et al (2008) in the paper published by Journal of Geophysical Research, similarly finds that “prior to 1965 the continent-wide annual trends (through 2002) are slightly positive, but after 1965 they are mainly negative (despite warming over the Antarctic Peninsula).”

Steig et al 2009 in the paper published by Nature, unlike all other major works, find significant warming trend over Antarctica 1957-2006, of 0.1 C per decade, although Steig’s reconstruction agree to greater extent with other studies in showing little temperature change since late 1960s.

Sea ice on Antarctica increased since satellite measurements began in 1979 0.6% per decade, and 2008 was on record level, and 2009 is also significantly above average.

Although the melting of Antarctic ice sheets is in public often associated with global warming, ice sheets on Antarctica also have grown, rather than melted. Wingham et al 20 showed “the Antarctic ice sheet growing at 5 ± 1 mm year-1 in period 1992-2003”. Using satellite altimetry technique, authors show that “72% of the Antarctic ice sheet is gaining 27 ± 29 gigatons per year.”

These results are very similar to the findings reported in paper published in Science by Curt Davis et al (2005), who also used satellite altimetry measurements of Antarctica to calculate mass changes, and estimated that over a similar period Antarctic ice sheets have grown 45 billion of metric tones per year at the pace that cause annual decline in sea level rise of 0.12 mm per year.

Unlike continent's interior, there is evidence for widespread glacier retreat around the Antarctic Peninsula.

The British Antarctic Survey, which has undertaken the majority of Britain's scientific research in the area, has the following positions about climate change on Antarctica: [3]

• Ice makes polar climate sensitive by introducing a strong positive feedback loop.
• Melting of continental Antarctic ice could contribute to global sea level rise.
• Climate models predict more snowfall than ice melting during the next 50 years, but models are not good enough for them to be confident about the prediction.
• Antarctica seems to be both warming around the edges and cooling at the center at the same time. Thus it is not possible to say whether it is warming or cooling overall.
• There is no evidence for a decline in overall Antarctic sea ice extent.
• The central and southern parts of the west coast of the Antarctic Peninsula have warmed by nearly 3°C. The cause is not known.
• Changes have occurred in the upper atmosphere over Antarctica.

NASA map showing snowmelt in areas where it never melted before

The area of strongest cooling appears at the South Pole, and the region of strongest warming lies along the Antarctic Peninsula. A possible explanation is that loss of UV-absorbing ozone may have cooled the stratosphere and strengthened the polar vortex, a pattern of spinning winds around the South Pole. The vortex acts like an atmospheric barrier, preventing warmer, coastal air from moving in to the continent's interior. A stronger polar vortex might explain the cooling trend in the interior of Antarctica. [4]