Southern hemisphere surface air temperature variations: 1851–1984

A new compilation of monthly mean surface air temperature data for the Southern Hemisphere for 1851–1984 is presented based on land-based meteorological station data. Where possible, the station data used in the analysis have been assessed for homogeneity. Only reliable or corrected station data have been used in calculating area averages. Grid point temperature estimates have been made by interpolating onto a 5° lat by 10° long grid for each month of the 134 years. For the period of best data coverage, 32% of the area of the Southern Hemisphere is covered. The reliability of hemispheric estimates is assessed for earlier periods when coverage is less than this maximum. Year-to-year estimates are considered reliable back to about 1890 and earlier estimates can indicate trends back to the 1860s. This new hemispheric compilation is compared with estimates of Southern Hemisphere marine data, and comparisons between land and marine data for both hemispheres are made and interpreted. The data show a long-term warming trend amounting to about 0.5°C over the past 100 years. The 1938–65 cooling trend that is so evident in the Northern Hemisphere data shows up only as a hiatus in the long-term warming of the Southern Hemisphere, pointing towards some hemispherically specific causal mechanism.