THE SUNDAY STORY An analysis of the output from 18 different global climate models indicates that India’s average annual surface air temperature could go up by between four degrees Celsius and seven degrees Celsius by the end of this century.

The warning signs are already out there. Global air and ocean temperatures have risen in response to human-driven emissions, particularly of carbon dioxide. Oceans have become more acidic and the sea level has gone up; the Arctic Sea ice has melted faster than expected; rainfall and snowfall patterns have changed; and extreme weather events seem more frequent than in the past. Such changes, with the associated consequences, are likely to worsen considerably if emissions continue unabated.

At the Climate Change Conference in Copenhagen in 2009, the nations of the world pledged to avoid ‘dangerous’ climate change by reducing emissions. They would ensure that the average global temperature at the end of this century did not exceed that of the pre-industrial period by more than two degrees Celsius. But as emissions continue to soar and with no meaningful global agreement in place to drastically cut them, there is increasingly talk of a temperature rise during this century of four degrees Celsius.

“A four degrees Celsius world would be one of unprecedented heat waves, severe drought, and major floods in many regions, with serious impacts on ecosystems and associated services,” warned a World Bank-sponsored report published last month.

India has already seen its average annual surface air temperature rise by about 0.5 degrees Celsius during the past century. The warming had accelerated since 1971 and particularly so during the past decade, according to the country’s Second National Communication to the U.N. Framework Convention on Climate Change made earlier this year.

Scientists use climate models, which have grown in sophistication, to simulate the impact that emissions produced by human activity will have on future climate. These models show a further sharp rise in temperatures over India as a result of climate change. An analysis of the output from 18 different global climate models, published recently by scientists from the Indian Institute of Science (IISc), Bangalore, and the IIT-Bombay, indicated that the country’s average annual surface air temperature could go up by between four degrees Celsius and seven degrees Celsius by the end of this century at the current rate of emissions.

Such large temperature increases would be detrimental to society and the country’s economy, said K. Krishna Kumar of the Indian Institute of Tropical Meteorology (IITM) in Pune. In such a scenario, the frequency and duration of heat waves was likely to increase substantially, taking a toll on human health. Agriculture too would be adversely affected by the rise in temperature.

What would happen to rainfall in the face of climate change, especially to the south-west monsoon that provides much of the precipitation the country receives, has proved more problematic to predict. For one thing, nationwide rainfall during the south-west monsoon has not shown any consistent trend over the last 140 years. Instead, the monsoon has displayed alternating periods of above-average and below-average rainfall.

Moreover, unlike with temperature, global climate models differ considerably in depicting how the monsoon will react to rising emissions. The combined output from the ensemble of 18 climate models studied by Indian scientists suggested that the monsoon might give 20 per cent more rain by the end of this century if emissions continued at the current rate.

Research published by B.N. Goswami of the IITM and other scientists showed that there had been a shift in rainfall patterns over central India in the latter half of the last century, with more heavy rainfall events and less moderate rain occurring. Several studies based on various climate models have given indications that episodes of heavy rain, along with fewer rainy days, could become frequent in large parts of the country later this century, said G. Bala of the Indian Institute of Science. Consequently, the country could face more floods and droughts as the climate continued to warm.

A warming of the global surface temperature by four degrees Celsius could lead to an associated sea level rise of 0.5 metre to one metre, noted the World Bank report. Many coastal areas in the country were vulnerable to rising sea levels as were the deltas of the Ganges, the Krishna, the Godavari, the Cauvery and the Mahanadi, according to India’s Second National Communication.

Besides, higher sea levels increase the damage a cyclone can unleash as it sweeps ashore. “Cyclones and storm surges could have a devastating impact on large urban centres, including the mega cities of Mumbai and Chennai,” as well as other coastal cities, the Second National Communication observed.

Although higher carbon dioxide levels and more rain can help crops grow better, higher temperatures and more erratic rainfall are often detrimental. For instance, the country’s wheat production could fall by about four million tonnes for every one degree Celsius rise in temperature during the crop’s growth period. Climate change, along with other environmental stresses, poses “significant challenges” for cereal production in China and India, according to a recent report from the U.S. National Intelligence Council.

Climate change will bring along it with new problems and challenges that must be faced.