Study forecasts extreme weather in future

Much of the world will see more deadly heat waves, intense rainstorms and prolonged dry spells before the end of this century, U.S. scientists predicted in a latest study.

The new study"Going to the Extremes," conducted by the researchers at U.S. National Center for Atmospheric Research, will appear in the December issue of the journal Climatic Change.

Previous climate studies have looked at how average temperature or rainfall might change in the next century as greenhouse gases increase, but the new work looks more specifically at how weather extremes could change, the researchers said.

"It's the extremes, not the averages, that cause the most damage to society and to many ecosystems," said Claudia Tebaldi, lead author of the report at the National Center for Atmospheric Research.

"We now have the first model-based consensus on how the risk of dangerous heat waves, intense rains, and other kinds of extreme weather will change in the next century."

The researchers based their work on simulations from nine different climate models for the periods 1980-1999 and 2080-2099. The simulations were created on supercomputers at research centers in France, Japan, Russia and the United States.

Each model simulated the 2080-2099 interval three times, varying the extent to which greenhouse gases increase. These three scenarios were used to account for uncertainty over how fast society may act to reduce emissions of carbon dioxide and other greenhouse gases over coming decades.

From the model output, the scientists computed 10 different indices of climate extremes, with five related to temperature and five to moisture.

For instance, a frost days index measures how many days per year temperatures dip below 0 degree Celsius, while a dry days index measures the length of each year's longest consecutive string of days without rain or snow.

The 10 indexes include: heat wave duration, the difference between a year's high and low temperatures, growing season length, frost days, warm nights and five factors involving precipitation.

Because the impact of a given index can be stronger in one climatic zone than another, the authors expressed the results in terms of statistical significance at each location.

For all three greenhouse-gas scenarios, the models agree that, by 2080-2099 the number of extremely warm nights and the length of heat waves will increase significantly over nearly all land areas across the globe.

During heat waves, very warm nights are often associated with fatalities because people and buildings have less chance to cool down overnight.

Most areas above about 40 degrees north, including northern part of the United States, Canada, and most of Europe, will see a significant jump in the number of days with heavy precipitation.

In addition, dry spells could lengthen significantly across the western United States, southern Europe, eastern Brazil, and several other areas. Dry spells are one of several factors in producing and intensifying droughts.

The average growing season could increase significantly across most of North America and Eurasia.

Most of these trends are significantly weaker for the lowest-emission scenario than for the moderate and high-emission scenarios, although extreme events were expected to occur more often than today.

Thus, the researchers noted, lowering the output of greenhouse gases over the next century should reduce the risk that the most severe changes will occur.

Source: Xinhua