A change in the latitudinal extent of the tropical belt can lead to substantial changes in local climate near its edges. The surface temperature gradient across latitudes is large near those edges, typically 1 K per degree latitude. So a shift of just 5° latitude in the tropical belt edge would lead to a local temperature change of about 5 K. Warming of that magnitude exceeds both the roughly 1-K average increase observed globally for the past century and the expected warming through the end of the 21st century. 7 Likewise, a shift in the pattern of evaporation and precipitation shown in figure 3 can dramatically change the local hydrological balance in the vicinity of the belt edges. Formerly humid areas may turn arid and vice versa. The changes would have major consequences for water availability for urban settlements, farming, ranching and herding, hydropower, and forestry. Natural ecosystems, including parklands, nature reserves, fisheries, and marine and estuarine ecosystems, are also sensitive to hydrological changes. Furthermore, an expansion of the tropical belt could lead to a poleward spread of vector-borne infectious diseases, such as malaria, dengue fever, and cholera. A change in the latitudinal extent of the Hadley cells is likely to move the location of the subtropical jet streams and thus shift the boundary of the Ferrel cells, with likely shifts in midlatitude storm tracks. Consequent water-cycle changes could strain human and natural systems in those areas too.
Posted on: Tue, 09 Dec 2014 08:27:26 +0000
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