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

Possible changes in the climate characteristics of the Northern Hemisphere in the 21st century are estimated using a climate model (developed at the Obukhov Institute of Atmospheric Physics (OIAP), Russian Academy of Sciences) under different scenarios of variations in the atmospheric contents of greenhouse gases and aerosols, 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 near-surface air temperature. The spatial structures of variations in the mean annual near-surface air temperature in the 21st century, which have been obtained for both groups of scenarios (with smaller absolute values for scenarios II), are similar. 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 near-surface air temperature increases by 2–4°C in North America and by 2–3°C in Eurasia. An increase in the total amount of precipitation 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 near-surface 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 near-surface 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 near-surface permafrost soils are preserved, the characteristic depths of seasonal thawing amount to 0.5–2.5 m for scenarios I and 1–2 m for scenarios II. In western Siberia, the depth of seasonal thawing amounts to 1–2 m under both scenarios I and II.