One important aspect of the observed temperature change over the globe during the past century relates to its asymmetry during the day and night (Karl et al., 1991). Observed warming in surface air temperatures over several regions of the globe has been reported to be associated with an increase in minimum temperatures (accompanied by increasing cloudiness) and a decrease in DTR (Hansen et al., 1998).
AOGCM simulations with increasing concentrations of GHGs in the atmosphere suggest relatively more pronounced increases in minimum temperature than in maximum temperature over Asia on an annual mean basis, as well as during the winter, for the 2050s and the 2080shence a decrease in DTR (Table 11-3). During the summer, however, an increase in DTR is simulated suggesting thereby that the maximum temperature would have a more pronounced increase relative to the minimum temperature (Lal and Harasawa, 2001). The summertime increase in DTR over central Asia is significantly higher relative to that in other regions. Most of the subregions follow the same pattern of change in DTR, except south and southeast Asia. A marginal increase in DTR during the winter and on an annual mean basis is simulated over southeast Asia. Over the south Asia region, a decrease in DTR on an annual mean basis and during the winter and a more pronounced decrease in DTR during the summer are projected. The significantly higher decrease in DTR over south Asia during the summer is a result of the presence of monsoon clouds over the region (Lal et al., 1996). In general, the decline in DTR is slightly moderated in the presence of sulfate aerosols (Lal and Harasawa, 2001). Changes in DTR over Asia in this case suggest a decrease in both seasons. Similar changes also are seen over boreal Asia and temperate Asia.
|Table 11-3: Projected changes in diurnal temperature range over Asia and its subregions under IS92a emission scenarios, as inferred from an ensemble of data generated in experiments with CCSR/NIES, CSIRO, ECHAM4, and HadCM2 AOGCMs.|
|Greenhouse Gases||Greenhouse Gases + Sulfate Aerosols|
|- Central Asia||0.13||-0.07||4.64||0.17||-0.11||4.75||-0.02||-0.14||2.20||0.09||-0.04||2.36|
|- South Asia||-0.27||-0.27||-3.06||-0.45
|- SE Asia||0.15||0.24||-0.50||0.00||0.09||-0.66||0.35||0.42||-0.98||0.18||0.24||-1.09|
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