The challenge to predict accurate monsoon becomes bigger in climate change scenario and a proposed system for predicting regional climate change would require an atmospheric Global Climate Model (GCM) which can resolve mesoscale cloud system with stratospheric chemistry, aerosol, dynamic vegetation, coupled to a carbon model and an oceanic GCM with biogeochemistry model. Speaking on ‘Knowns and Unknowns of Indian Summer Monsoon in a Changing Climate’ at the 98th Indian Science congress at Chennai today, Prof B N Goswami from Indian Institute of Tropical management, Pune said, “Unprecedented increase in global temperature and widespread occurrences of climatic anomalies around the globe endorses that earth’s climate is undergoing a phenomenal change. All over the globe warmest years and changes in ea level, glacier structure and rise in temperature occurred including India which witnessed increased trend in mean surface temperature. The year 2009 was the warmest year in the country in the past 100 years. He added, “ Global Climate Models taking part in the IPCC 4th assessment report indicate that the increase in temperature in recent decade is most likely due to anthropologenic green house gases (GHGs).The current concentration of CO2 and CH4 in the atmosphere is 30% . They are 3 times larger than highest levels seen during the past one million years.”
Discussing the possible effects of these changes on Indian summer monsoon, mean Indian summer Monsoon rainfall and responses, Prof Goswami categorically said that The effective predictions of monsoon weather demand quantum leap in improvement of observations, better prediction system and high computing power. He explained, “The increasing trend in frequency and intensity of extreme rain events over Central Indian (CI) may be attributed to the increasing instability. While the extreme rain events over north-east India are declining in compliance with a decreasing trend in convective instability. The consequence of the energized high frequency scales are its influence on the potential predictability of monsoon weather. High active frequency scales would cause faster growth and saturation of very small initial errors. It reduces the potential predictability of weather scales through upscale cascade of errors. The average error doubling time computed using India Meteorological Department (IMD) daily gridded rainfall data from 1901-2004 over Central India. This error doubled in recent quarter of 100 year period and hence become almost difficult to predict during the recent decades.” Regarding cyclones and depressions Prof Goswami said the number of cyclones have decreased but depressions have increased. Despite general consensus among models in predictions, they do not project the Summer Monsoon Rainfall over south Asia with fidelity. Uncertainty on projection of Indian monsoon also arises from the fact that monsoon is affected by certain feed backs within the climate system.”
It is essential to get the climate models simulate present day monsoon climate accurately before we can attempt climate change projections, Prof Goswami said. Global cloud resolving models seems to simulate the observed mesoscale clusters correctly, but they are very expensive.