As global warming accelerates, people the world over are growing more concerned with summer heat waves, melting glaciers, rising sea levels and disturbed ecosystems.

But scientists are now calling on the public to be more aware of other potential threats, which they believe are neglected.

Water shortages, for instance, will become one of the most serious problems facing the world in the future, according to Syukuro Manabe, a senior US meteorologist.

Manabe made the remarks in a press conference at the ninth convention of the International Association of Meteorology and Atmospheric Sciences, which will end tomorrow in Beijing.

World leading meteorologists have been in the Chinese capital since last week to discuss a wide range of atmospheric and meteorological issues, such as air pollution, global climate change, precipitation and extreme climate.

The first scientist in the world to build computer models predicting climate change, Professor Manabe, from the Department of Geosciences at Princeton University, is known as the forefather of greenhouse gas.

As the concentration of greenhouse gases, such as carbon dioxide, methane, and water vapor, increase in the atmosphere, more water on the earth's surface will evaporate, he said.

And because the air can't hold that much water, there will be more precipitation.

"But the change is not uniform everywhere. Some places get drier while other places get more water," Manabe said.

In regions where precipitation is substantially greater than potential evaporation, more rain means more runoff.

In regions where rainfall barely increases or even decreases when temperatures climb, soil moisture slides.

In fact, according to Professor Manabe, soil is getting drier in many semi-arid regions across the world, including the southwestern region of North America, the northeast of China, the Mediterranean coast of Europe and the grasslands of Africa and Australia.

"With enough water, these regions could be ideal agricultural bases because of their fertile soil and abundant sunshine," Manabe said.

"Unfortunately, rainfall in these regions is not likely to increase significantly, or may actually decrease slightly, as global warming continues. So the water shortage there will be acute in the next few centuries," Manabe added.

In contrast, an increasingly excessive amount of water is likely to be available in water-rich regions in high northern latitudes.

The mean global temperature has climbed 0.7 degrees Celsius since the beginning of the Industrial Revolution. By the latter half of this century, world temperatures will probably see a rise of 2-3 degrees on average, Manabe said.

In higher latitudes, the temperature increase could be as much as 4 to 8 degrees by the end of the century.

"As the ground cover of snow and ice is replaced by soil with increased temperatures in these regions, less sunshine will be deflected, which, in a way, would intensify the warming effect," Manabe said.

Prepared for a warmer world

Meteorologists have been using computer models to calculate which factor is most likely to contribute to climate change.

"It seems that human activities play a major role in the process," said Michael MacCracken, president of the international association.

Over the past decades, meteorologists have been looking closely at how climate will be affected by carbon dioxide emissions a topic on which they have issued repeated warnings.

"To avoid dangerous consequences of global warming, all countries, both developed and developing, should do all they can to limit carbon emissions," said Michael.

However Professor Manabe said it was difficult to control emissions as many countries could not afford to curtail them, and warned that the concentration of carbon dioxide would only increase in coming decades and centuries.

"That is why we are trying hard to predict what possible negative consequences might accompany global warming. We had better make preparations for them right now," Manabe said.

The world is already suffering a water shortage. It has little to do with global warming and is mainly a result of large-scale irrigation, huge wastage of water, and other human activities, according to Manabe.

"If we think what we should do with water problems right now, it would be a very good step towards solving future water shortages," he said.

(China Daily August 10, 2005)