Figure 2 Deviation of the annual mean surface air temperature corrected to elevation effect from the zonal average temperatures (a), and the magnitude of seasonal variations of surface air temperature (b). The data are from Legates DR and Willmott CJ (1990) Mean seasonal and spatial variability in global surface air temperature. Theoretical and Applied Climatology 41: 11-21.

reorganization of the thermohaline circulation also affects the hydrological cycle. In particular, cooling of surface North Atlantic reduces evaporation in this area which causes a drastic reduction of precipitation over most of Europe. Another important result of the Atlantic thermohaline circulation weakening is a southward shift in the position of the intertropical convergency zone (ITCZ), which is associated with the rain belt around the equator. Shift of ITCZ causes a considerable redistribution of precipitation in the tropics, with a decrease of precipitation north of the equator and an increase south of the equator. It also affects the strength of subtropical monsoons, with weaker Indian and African monsoons. It is also plausible that regime change of the Atlantic circulation can directly affect tropical Pacific, in particular, El NiƱo/Southern Oscillation cycle, which is responsible for a large portion of climate variability in the tropics and affects climate over the globe. Not all of the aforementioned processes are well understood and fundamental limitations of current climate models preclude unambiguous conclusion about possibility of the abrupt changes of the oceanic circulation in the future, but a growing body of paleoclimatological data indicates that, at least in the past, rapid and vigorous changes in the ocean circulation occurred regularly and had a widespread impact on climate and biosphere. Thereby, the possibility of abrupt climate shifts caused by changes of the ocean circulation remains one of the concerns related to anthropogenic global warming.

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