Estimating climate changes in the northern hemisphere in the 21st century under alternative scenarios of anthropogenic forcing

Abstract

Possible changes in the climate characteristics of the Northern Hemisphere in the 21st century are esti� mated using a climate model (developed at the Obukhov Institute of Atmospheric Physics (OIAP), Russian Acad� emy of Sciences) under different scenarios of variations in the atmospheric contents of greenhouse gases and aero� sols, including those formed at the OIAP on the basis of SRES emission scenarios (group I) and scenarios (group II) developed at the Moscow Power Engineering Institute (MPEI). Over the 21st century, the global annual mean warming at the surface amounts to 1.2-2.6°C under scenarios I and 0.9-1.2°C under scenarios II. For all scenarios II, starting from the 2060s, a decrease is observed in the rate of increase in the global mean annual nearsurface air temperature. The spatial structures of variations in the mean annual nearsurface air temperature in the 21st cen� tury, which have been obtained for both groups of scenarios (with smaller absolute values for scenarios II), are sim� ilar. Under scenarios I, within the extratropical latitudes, the mean annual surface air temperature increases by 3- 7°C in North America and by 3-5°C in Eurasia in the 21st century. Under scenarios II, the nearsurface air tem� perature increases by 2-4°C in North America and by 2-3°C in Eurasia. An increase in the total amount of pre� cipitation by the end of the 21st century is noted for both groups of scenarios; the most significant increase in the precipitation rate is noted for the land of the Northern Hemisphere. By the late 21st century, the total area of the nearsurface permafrost soils of the land of the Northern Hemisphere decreases to 3.9-9.5 10 6 km 2 for scenarios I and 9.7-11.0 × 10 6 km 2 for scenarios II. The decrease in the area of nearsurface permafrost soils by 2091-2100 (as compared to 2001-2010) amounts to approximately 65% for scenarios I and 40% for scenarios II. By the end of the 21st century, in regions of eastern Siberia, in which nearsurface permafrost soils are preserved, the charac� teristic depths of seasonal thawing amount to 0.5-2.5 m for scenarios I and 1-2 m for scenarios II. In western Sibe� ria, the depth of seasonal thawing amounts to 1-2 m under both scenarios I and II.