Global climate change in the history of earth is a natural phenomenon due to continental drift, earth axis and orbital variations, variants in solar energy output and frequent volcanic activity. With the end of Little Ice Age (15th to 18th centuries), the behaviour of average surface temperature on earth depicts an increasing trend. Over the past few decades, since industrialization human activities have resulted in steady increased concentrations of greenhouse gases in the atmosphere, which lead to the enhanced greenhouse effects, and thereby cause global warming. Over the past hundred years, the world?s average surface temperature has increased between 0.3° C and 0.6° C. Ten warm years have already has been recorded in this century. The 1990s were likely to be the warmest decade of the millennium in the Northern Hemisphere, and the year 1998 was the warmest year, followed by the second warmest year 2005. According to the Intergovernmental Panel on Climate Change (IPCC 2001), and its assessments based on climate models, the increase in global temperature will continue to rise during the 21st century. The mean global temperature is the average from 1961 ? 1990, assumed as normal period. The increase in the global mean temperatures from 1990 to 2100 could amount to anything from 1.4° C to 5.8° C, depending on the climate model and greenhouse gases emission scenario. On the Indian sub-continent temperatures are predicted to rise above an average between 3.5° C and 5.5° C by 2100.
Mountain Forum Bulletin 'Melting Mountains' July 2007
