A synthesis of Antarctic temperatures

Monthly surface air temperatures from land surface stations, automatic weather stations, and ship/ buoy observations from the high- latitude Southern Hemisphere are synthesized into gridded analyses at a resolution appropriate for applications ranging from spatial trend analyses to climate change impact assessments. Correlation length scales are used to enhance information content while limiting the spatial extent of influence of the sparse data in the Antarctic region. The correlation length scales are generally largest in summer and over the Antarctic continent, while they are shortest over the winter sea ice. Gridded analyses of temperature anomalies, limited to regions within a correlation length scale of at least one observation, are constructed and validated against observed temperature anomalies in single- station- out experiments. Trends calculated for the 1958 - 2002 period suggest modest warming over much of the 60 - 90 S domain. All seasons show warming, with winter trends being the largest at + 0.172 degrees C decade 1 while summer warming rates are only +0.045 degrees C decade(-1). The 45-yr temperature trend for the annual means is +0.082 degrees C decade(-1) corresponding to a +0.371 degrees C temperature change over the 1958 - 2002 period of record. Trends computed using these analyses show considerable sensitivity to start and end dates, with trends calculated using start dates prior to 1965 showing overall warming, while those using start dates from 1966 to 1982 show net cooling over the region. Because of the large interannual variability of temperatures over the continental Antarctic, most of the continental trends are not statistically significant. However, the statistically significant warming over the Antarctic Peninsula is the strongest and most seasonally robust in the spatial patterns of temperature change. Composite ( 11- model) global climate model ( GCM) simulations for 1958 - 2002 with forcing from historic aerosol and greenhouse gas concentrations show warming patterns and magnitudes similar to the corresponding observed trends for the 45- yr period. GCM projections for the rest of the twenty- first century, however, discontinue the pattern of strongest warming over the Antarctic Peninsula, but instead show the strongest warming over the Antarctic continent.