The Hindu : Our future climate

Online edition of India's National Newspaper
Sunday, Mar 23, 2003

Opinion

Opinion - News Analysis

Our future climate

By Y.E.A. Raj and P.V. Sankaran

The theme for World Meteorological Day - 2003, being commemorated on March 23, is `Our Future Climate'. Climate is essential and central for sustaining life on earth and plays an important role in shaping the lifestyle and culture of its people. There is growing evidence of anthropogenic changes to our climate that have become conspicuous in recent decades. For e.g., the 1990s were the warmest decade since 1860 when instrumental observations began, with 1998 being the warmest followed by the year 2001. The warming has been linked to the growth in the concentration of greenhouse gases in the atmosphere such as carbon dioxide, methane and nitrous oxide, which have shown an increase of 32, 151 and 17 per cent respectively over the past two centuries.

The global warming has resulted in the rise of global mean sea level by 10-20 cm, decrease in sea ice by 10-15 per cent, decline of Arctic sea ice thickness by nearly 40 per cent and retreat of mountain glaciers. The frequency of extreme weather events such as floods, tropical cyclones and droughts have shown an increase in recent years. In 2002, unprecedented floods have caused enormous destruction in Europe, China and Korea whereas parts of Asia, Africa and United States have been affected by severe drought. In the last decade, there has been a doubling of hydro meteorological disasters over the globe which included the strongest El-Nino of the century in 1997-98 which affected 11-crore people and cost the global economy nearly $ 100 billion. Winters have become milder and summer harsher in several countries.

The concentration of carbon dioxide — one of the greenhouse gases — in the atmosphere has increased from 280 parts per million (PPM) in 1750 to 370 ppm at present. If the present trend were to be maintained, the concentration will reach 540-970 ppm in 2100. A matter of concern is that, even if emission of a long-lived greenhouse gas such as carbon dioxide into the atmosphere were to be totally curtailed today, the gas could stay up in the atmosphere for another 200 years. Certain changes in the climate system for e.g., melting of ice sheets and major changes in the ocean circulation patterns which can take place in the 21st century would be almost irreversible.

The earth's climate system is chaotic thus limiting predictability. However, the threat of climate change requires projection of possible future events to enable identification of policy options to meet the challenge. Considerable amount of research has therefore been directed in recent years towards developing comprehensive climate models based on physical systems such as atmosphere, ocean, land etc. Some of the model projections of the future climate events are:

* Increase of global mean temperature by 1.4-5.8 degree Celsius 2100.

* Increase of sea level by 9-88 cm from the 1990 level by 2100.

* More hot days and heat waves, increase in heat index.

* Decrease in cold waves and frost days.

* Increase in precipitation extremes, viz. floods and droughts.

There are both positive and negative consequences of the above projected climate changes. The negative impacts are:

* General reduction in potential crop yield in most tropical and sub-tropical regions.

* Decrease in winter rainfall of Australia, Central America and Southern Africa.

* Increased risk of coastal flooding and erosion, drinking water salinisation.

Some of the positive impacts are:

* Increase of crop yield in mid-latitude countries.

* Increase of precipitation by 5-10 per cent over higher latitudes.

* Reduced winter mortality in extra tropics.

Now, what is the manifestation of global climate change in India? Studies have shown that rainfall over India, both monsoon and annual, has not displayed any trend during the last 100 years. In fact, India received above or near normal rainfall during the 14-year period, 1988-2001, whereafter the run of good monsoons was broken by the drought of 2002. By and large, individual States and meteorological subdivisions have also not displayed any rainfall trend though in smaller regions such as districts, rainfall trends both negative/positive might have been registered. As for surface temperature, mild warming tendency of 0.2-0.4 degree Celsius for 100 years has been documented, when averaged over the whole of India. Studies based on long-term data have shown that mean tide level has shown a rising trend of 0.8, 1.2 and 0.9 mm per year at Mumbai, Kochi and Visakhapatnam. In case of atmospheric circulations, the monsoon depressions are one of the major rain-bearing systems (of Indian monsoon) that form over the Bay of Bengal and move into the Indian land mass. Their frequency has substantially declined since 1991 from a decadal average of 14.8 during 1891-1990 to just 3 in 1991-2000, though there has not been any negative fallout of the above decrease in terms of rainfall. It might appear that effect of global climate change over India has not been that conspicuous. However, this should not brook any complacency (on the part of India) in addressing the core issues involved in global warming, as the negative effects of climate change will eventually affect India as well. For record, India stands sixth among 20 largest carbon dioxide emitting countries, accounting for 3.6 per cent of the total emissions of the world.

The World Meteorological Organisation, with the active participation of all the National Meteorological Services proposes to continue its leading role in addressing the core scientific and technical issues involved in global warming. The first issue relates to improvement of observations and hence the reconstruction of past climate periods. The second is to develop robust models which could address the uncertainties inherent in long-term climate prediction. The third is the dissemination of advanced products to all the countries and in providing necessary support to the National Meteorological Services. Progress in addressing these issues will reduce the uncertainties of climate prediction besides providing improved long-term climate forecasts at national as well as basin levels.

(The writers are Director and Assistant Meteorologist respectively at the Regional Meteorological Centre, Chennai.)

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