Temperatures have shown a rising trend over the past century, more so in recent decades. Depending on how the trend persists or scales up, India will have to face the harsh consequences of climate change in the coming decades.
(Chart is based on the surface air temperature data from more than 350 meteorological stations spread over the country. )
Temperature data over the past century or so shows that India has experienced a long-term mean temperature rise of over half a degree Celsius, but the million dollar question relates to the future - how much warmer will the country country be towards the end of this century? That is because the scale of temperature change will determine the climate change outcome.
But change there will be and not for the better if the temperature rise continues. The UN had in June released a report that pointed to unusual extreme heat over 20 percent of the South Asia land area during summer months in the Northern hemisphere if global warming was under 2 degrees Celsius by 2100. The report, titled 'Turn down the heat: the climate extremes, regional impacts, and the case for resilience,' said "unprecedented heat extremes" would affect about 5 percent of the land area, mainly in the south.
If the warming was under 4°C, the west coast and southern India would be among the regions that were "projected to shift to new, high-temperature climatic regimes."
"Under future climate change, the frequency of years with above normal monsoon rainfall and of years with extremely deficient rainfall is expected to increase."
"At 4°C global warming, sea level is projected to rise over 100 cm by the 2090s, monsoon rainfall to become more variable with greater frequency of devastating floods and droughts. Glacier melting and snow cover loss could be severe, and unusual heat extremes in the summer months (June, July, and August) are projected to affect 70 percent of the land area. Furthermore, agricultural production is likely to suffer from the combined effects of unstable water supply, the impacts of sea-level rise, and rising temperatures."
Different models have projected temperature rise of different orders over the coming decades for India, but past data graphically tells us that a temperature rise has been witnessed over the past century. And that it has accelerated in recent decades.
The mean temperature data over the past century shows that the 'warmest' years during this period have occurred since 1995.
The annual mean temperature for the country as a whole has risen by 0.56 degrees Celsius said an India Meterological Department document on the basis data analysed for the period 1901-2009. The annual mean temperature has been 'above normal' since 1990, if the normal temperature is based on the data pertaining to the period 1961 to 1990. The warming was attributed mainly due to the rise in maximum temperature across the country. But since 1990 the minimum temperature has also been steadily rising and the rate at which this has been happening is "slightly more" than that of the maximum temperature rise.
Most parts of the country have seen an increase in the mean annual temperature but parts of Rajasthan, Gujarat and Bihar are exceptions, where it has been falling.
The warmest ten years based on average mean temperatures recorded over the past century:
|Year||Temperature (degrees Celsius)|
India's Second National Communication to the United Nations Framework Convention on Climate Change finalised in 2012 also speaks of "intense warming in the recent decade (1998–2007)." It has attributed the overall temperature increase mainly to the increase during the winter and post-monsoon seasons. The change has been as much as 0.70° C during winter and 0.52°C during monsoon over the last century or so (1901 - 2007). Pre-monsoon and monsoon temperatures have also been rising.
The mean temperature increased by about 0.2°C per decade between 1971–2007, with the minimum temperatures increasing much more than the maximum temperature. The maximum temperature rose much more steeply during the past decade compared to the past century and the increase in minimum temperature during the past decade was almost equal to the increase observed between 1971 and 2007.