Weather & Climate | VOL. 12, ISSUE 75, November-December 2012

Global Warming and Indian Monsoon

It has been observed since 1979 that there is a heterogeneous increase in the tropospheric temperature across the globe. The rise in tropospheric temperature over selected climatic zones during the period 1949-1978 is as follows - the equator +0.45°C, the north polar +0.60°C, the north subtropic +0.32°C, the south subtropic +0.77°C and the south polar region +0.66°C, recording a higher increase in the polar regions as compared to the equator. Consequently, a decrease in the tropospheric temperature gradient from equator to poles is also observed causing a weakening of the general atmospheric circulation. Further, there is a decrease in the boreal summer tropospheric temperature gradient in Tibet causing weakening of the Asia-India monsoon circulation and all-India monsoon rainfall, which during the 1999-2012 has reduced by 6.1 per cent (857mm) compared to the period 1949-1998 (913mm). Monitoring Global Warming The difference in the 12 month mean of the tropospheric temperature between equator and the different climatic zones has indicated a general decline in the thermal contrast from mid-1970s and more sharply in recent decades (Fig 1) – the highest being between the equator and south polar region in the past decade. In fact, the whole depth of the troposphere is warming across the globe though at different rates. In general, the southern hemisphere is warming at a faster rate than the equator and the northern hemisphere,...

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