Scientists know the Antarctic ice sheet is losing mass “100 years ahead of schedule” (see “AGU 2008: Two trillion tons of land ice lost since 2003” and “Antarctic ice sheet hits the fan“).
Now, as Nature‘s climate blog reports, two studies presented last week at the AGU meeting document what should not be a surprise, but still is. New research suggests “the entire Antarctic continent may have warmed significantly over the past 50 years“:
The study, led by Eric Steig of the University of Washington in Seattle and soon to be published in Nature, calls into question existing lines of evidence that show the region has mostly cooled over the past half-century.
… they found warming over the entire Antarctic continent for the period 1957-2006. Restricting their analysis to 1969 to 2000, a period for which other studies have found a net cooling trend, Steig’s study found slight cooling in east Antarctica, but net warming over west Antarctica.
How did they perform the analysis of the harshest, most remote climate on the planet?
Steig and colleagues combined satellite thermal infra-red collected over 25 years with weather station data for the region. Although the satellite data span a shorter time period and are accurate only for blue sky days i.e. when there is no cloud cover, they provide high spatial coverage of the region, which cannot be obtained from discrete ground measurements. In contrast, the weather station data provide complete temporal resolution over the past half-century….
They independently confirmed these trends by using data from automatic weather stations, and excluding the satellite data.
Turns out they were not the only study to present at the AGU meeting to find that warming extends beyond the Antarctic’s Peninsula region. David Bromwich of the Byrd Polar Research Centre at Ohio State also presented at AGU his new study, “Surface and Mid-tropospheric Climate Change in Antarctica,” which found:
Near-surface air temperatures and 500-hPa temperatures over Antarctica for 1960-2007 have been reconstructed over the entire continent using manned station observations and radiosonde records, respectively, from the READER database maintained by British Antarctic Survey. The 50-year trends found in our near-surface temperature reconstruction agree with recent work by others using a variety of spatial extrapolation techniques. It is found that the statistically significant Antarctic Peninsula near-surface warming on an annual basis has spread into West Antarctica reaching as far as east as the Pine Island Bay-Thwaites Glacier region.
The warming is most marked in recent years with 2007 being the warmest year in the 1960- 2007 interval…. The warming over West Antarctica is maximized in the spring (SON) and in that season statistically significant warming stretches across all of West Antarctica and into northern Victoria Land. Weak near- surface warming is found over East Antarctica and the continent as a whole on an annual basis although continental warming in the spring is statistically significant and driven largely by the strong and widespread changes in West Antarctica.
How credible and comprehensive is this research? It is based on a three-year study funded by the National Science Foundation’s Office of Polar Programs (Glaciology), in which Bromwich worked with the U.S. National Center for Atmospheric Research and the British Antarctic Survey. As Bromwich explains on his website, he blended model data and observations “to reconstruct a record of Antarctic near-surface temperature back to 1960”:
Considering that there are only 15 long-term observational records of near-surface temperature over the entire continent of Antarctica (1-1/2 times the size of the U.S.), this record fills important gaps in our current knowledge of the spatial and temporal variability of Antarctic near-surface temperatures. Only two other such observational records – that depict temperatures over the entire continent – exist. We have collaborated with the creators of the other two datasets … to perform the most comprehensive evaluation of Antarctic near-surface temperatures yet….
The key finding is that temperatures over most of Antarctica have been warming subtly since the early 1990s, consistent with a leveling-off of trends in the Southern Hemisphere Annular Mode over the same period. This result contrasts with most recent results indicating the temperatures over Antarctica (other than on the Antarctic Peninsula) haven’t changed much in recent decades.
So notwithstanding the amateur meteorologist-deniers who sometimes comment on this blog and elsewhere about how cold it is outside right now, the whole damn planet is warming and melting.
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