Latitudinally asymmetric response of global surface temperature: Implications for regional climate change

The Earth's climate system was subject to two multidecadal warming trends in the beginning (1910-1940) and end (1975-2005) of the 20th century, having been interrupted only by a cooling trend in mid-century (1940-1975). The spatio-temporal distribution of surface temperature during this time, especially the land-ocean warming contrast in recent decades, has been the subject of many climate change detection studies. The focus of this study is the south-to-north warming asymmetry and we observed a similar Latitudinal Asymmetry of Temperature Change (LATC) for the two warming sub-periods and the cooling sub-period. Basically, the temperature change was low in the Southern Hemisphere extra-tropics (60 degrees S) and increased monotonically to peak values (0.15 degrees C/decade for warming trends) in the Northern Hemisphere extra-tropics (60 degrees N). We hypothesized that the LATC is a fundamental characteristic of the planet's transient response to global forcing. We tested this hypothesis using climate model simulations of CO2 and aerosol forcing, and the simulations revealed very similar LATC as seen in the observations. In the simulations, the LATC did not depend on the asymmetry of the forcing and furthermore weakened significantly in equilibrium simulations, leading to the deduction that the LATC was caused by a corresponding asymmetry in the land-ocean fraction, i.e., the analyses of model simulations supported the hypothesis of LATC being a fundamental characteristic of the planet's transient response. If LATC is preserved as the planet warms beyond 2 degrees C, precipitation patterns can be drastically disrupted in the tropics and sub-tropics, with major implications for regional climate. Citation: Xu, Y., and V. Ramanathan (2012), Latitudinally asymmetric response of global surface temperature: Implications for regional climate change, Geophys. Res. Lett., 39, L13706, doi:10.1029/2012GL052116.