Regional cooling does not disprove global warming. In any case, Antarctica has warmed overall over the past 50 years
Even if Antarctica was getting cooler, it would not mean the world as a whole isn’t warming. Climate models do not predict an even warming of the whole planet: changes in wind patterns and ocean currents can change the way heat is distributed, leading to some parts warming much faster than average, while a few may cool, at least at first.
The overall picture is indisputable: global temperature maps show far more areas are warming than cooling. As warming continues as emissions continue to rise, eventually every part of the world will warm.
So what is happening in Antarctica? There has been uncertainty over exactly how Antarctica’s climate is changing. There are few weather stations, most are on the edge rather than in the interior of the continent and records go back just a few decades.
There is no doubt that the Antarctic Peninsula, which juts out from the mainland of Antarctica towards South America, has warmed significantly. A 2002 study, however, concluded that between 1966 and 2000 the continent’s interior cooled.
This study was promptly seized upon as proof that the world is not warming, even though a single example of localised cooling proves no such thing, as the lead author of the 2002 study has tried to point out.
A more recent and more comprehensive study has concluded that in fact Antarctica warmed by 0.5 °C between 1957 and 2006, with especially strong warming in West Antarctica.
GISS Surface Temperature Analysis
Global Maps from GHCN v3 Data
You may generate a surface temperature anomaly or trend map using the following form. An explanation of the input elements is appended below.
Note: Generating figures takes 5-10 seconds. Please be patient.
Data Sources: Land:
Time Interval: Begin — End
Base Period: Begin — End
Notes concerning the maps:
The number at the top right-hand corner is an estimate for the global mean. Missing data are replaced by the zonal mean to find that estimate. However, if the map only shows ocean data, the mean is computed only over the area with data (added 12/13/2010).
The end points of the color bar are either -4.1 or +4.1 or the minimum or maximum value of the data if it is outside that range.
Data Sources: Land
None: NO land temperature data are used
GISS analysis (updated each month) (Hansen et al. 2010 and Updates to Analysis)
Data Sources: Ocean
None: NO ocean temperature data are used
1880-11/1981: Hadley HadISST1, ship and buoy data (Rayner 2000),
12/1981-present: oisst v2, satellite data (Reynolds-Rayner-Smith 2001)
Anomalies: Mean temperature (°C) averaged over a specified mean period and time interval relative to a given base period.
Trends: Temperature change of a specified mean period over a specified time interval based on local linear trends.
Mean period: Any monthly, seasonal (3 month or 6 month) or annual mean.
Period is declared missing, unless>50% of data are available.
Time interval: Years over which temperatures are averaged or trends are found.
If the mean period straddles 2 years, fill in the LATER year for both Begin AND End.
Periods may not start before Jan 1880.
‘Means’ are not reported unless>50% of the needed records are available,
‘Trends’ are not reported unless>66% of the needed records are available.
Base period: Time interval to which anomalies are relative. This input is not used for trend maps.
Smoothing radius: Distance over which a station influences regional temperature, either 250 km or 1200 km (standard case = 1200 km).
Blowing in circles
This does not mean the 2002 study was completely wrong. The latest study also found that for the period 1969 to 2000, there has been slight cooling over East Antarctica.
So what is going on? The cooling is due to a strengthening of the circular winds around the continent, which prevent warmer air reaching its interior. The increased wind speeds seem to be a result of cooling in the upper atmosphere, caused by the hole in the ozone layer above the pole, which is of course the result of chlorofluorocarbon (CFC) pollution.
Confusingly, it appears that one human impact on the climate – the Antarctic ozone hole – is currently compensating for another, global warming. If the ozone layer recovers over the decades as expected, the circular winds could weaken, resulting in rapid warming across the entire continent.
This raises the question of what is happening to Antarctica’s ice sheets, which hold enough water to raise sea level by a catastrophic 61 metres, should it all melt. Contrary to what you might expect, the third IPPC report predicted that global warming would most likely lead to a thickening of the ice sheet over the next century, with increased snowfall compensating for any melting cause by warming.
Finding out what is actually happening to the ice is not easy. Radar measurements of the height of the ice over parts of the continent suggest that the huge East Antarctic ice sheet grew slightly between 1992 and 2003.
A more recent study based on satellite measurements of gravity over the entire continent suggests that while the ice sheets in the interior of Antarctica are growing thicker, even more ice is being lost from the peripheries. The study concluded that there was a net loss of ice between 2002 and 2005, adding 0.4 millimetres per year to sea levels (see Gravity reveals shrinking Antarctic ice). Most of the ice was lost from the smaller West Antarctic ice sheet.
Greenland, whose ice cap holds enough water to raise sea levels by 7 metres, is also losing ice overall.
The IPCC’s latest prediction for sea level rise – 0.2 to 0.6 metres by 2100 – takes this ice loss into account but it is based on the assumption that the rate of ice loss will remain constant. Many researchers think this is unrealistic and that the rate of ice loss will accelerate, which means that sea level could rise much faster than predicted. But no one knows for sure what will happen and the prediction of a net gain of ice in Antarctica could yet turn out to be correct.