Climate scientists who want to know how average temperatures on Antarctica might be changing must wrestle with the fact that ground-based weather stations are few and far between, especially in the continent's high-altitude interior. Although automated weather stations are generally assumed to be the most accurate record-keepers, their sparseness makes it hard for scientists to be confident of what is happening across the entire continent. In addition, the harsh environment takes a toll on equipment, and long gaps of missing data interrupt the time series of some stations.
Although satellite-based temperature records have their own limitations (most significantly, cloud interference), they provide a complete, continuous view of the continent from the early 1980s onward. Scientists from NASA’s Goddard Space Flight Center have been working for several years to create and refine a satellite map of long-term temperature change in Antarctica. This image illustrates long-term changes in yearly surface temperature in and around Antarctica between 1981 and 2007. (An earlier version of this map is pictured in a previous posting on the Earth Observatory.) Places where it warmed over time are red, places where it cooled are blue, and places where there was no change are white.
The map is based on thermal infrared (heat) observations made by a series of National Oceanic and Atmospheric Administration satellite sensors. Because the satellite is observing energy radiated from the Earth’s surface, the image shows trends in skin temperatures—temperatures from roughly the top millimeter of the land, sea ice, or sea surface—not air temperatures. Making a long-term record out of data from different sensors is challenging because each sensor has its own quirks and may measure temperatures a bit differently. None of the sensors were in orbit at the same time, so scientists could not compare simultaneous observations from different sensors to make sure each was recording temperatures exactly the same. Instead, the team checked the satellite records against ground-based weather station data to inter-calibrate them and make the 26-year satellite record. The scientists estimate the level of uncertainty in the measurements is between 2-3 degrees Celsius.
Across most of the continent and the surrounding Southern Ocean, temperatures climbed. In some places the rate of warming approached a tenth of a degree Celsius each year, which would translate to more than two degrees over the entire period. The most dramatic changes appear as solid red streaks and splotches. In most cases, these changes are likely linked to major iceberg calving events on the ice shelves that fringe the Antarctic coastline, including the Ross Ice Shelf and the West and Shackleton Ice Shelves in East Antarctica. In the case of the Larsen B Ice Shelf on the Antarctic Peninsula, the entire ice shelf collapsed. After the calving or collapse, the satellite saw open water where there had previously been ice, so the temperature increase was stark.
The temperature increases were greater and more widespread in West Antarctica than in East Antarctica, where some areas showed little change or even a cooling trend. This variability in temperature patterns across Antarctica complicates the work of scientists who are trying to understand the relative influence of natural cycles and human-caused climate change in Antarctica.
NASA image by Robert Simmon, based on data from Joey Comiso, GSFC.