Observed twentieth century land surface air temperature and precipitation covariability

Significant positive trends in surface air temperatures (SATs) and precipitation were observed over 71% and 27%, respectively, of the global land surface during the twentieth century. Although the terrestrial surface is becoming warmer and wetter, the covariability between annual SAT and precipitation is not well understood. Significant anticorrelations between annual values of SAT and precipitation exist over 24% of the global land surface. Regional-scale interannual climate variability alternates between two dominant regimes, namely relatively warm and dry or cool and wet conditions. The out-of-phase positive trends in terrestrial SATs and precipitation observed during the twentieth century provide an important climate simulation benchmark.