The 100-Year Forecast: More Extreme Weather

The recent spate of heat waves and heavy rain and snow storms afflicting certain parts of the globe could become more widespread by the end of the century, scientists say.

An international team of researchers formed their conclusion after running computer simulations predicting what future weather patterns around the globe will look like if levels of greenhouse gases continue to rise as expected.

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The simulations were run three times, with greenhouse gases set at either low, medium or high. All three scenarios predicted increases in extreme weather but differed regarding their frequency.

"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," said study team member Claudia Tebaldi of the National Center for Atmospheric Research (NCAR).

Behind the model

Researchers used gathered data to simulate global weather patterns for the years 1980 to 1999. This information was then used to simulate weather patterns for 2080 to 2099.

Since scientists currently disagree on how fast levels of greenhouse gases will rise, or how fast society might counteract the increase, the future simulations were run with three different sets of assumptions. For each simulation, the researchers tracked 10 different markers of climate change, including how many frost days and dry days there were per year.

For all three global warming scenarios, the models agreed that by the end of the century:

• The number of extremely warm nights and the length of heat waves for land areas around the globe will increase significantly.

• Most areas above 40 degrees North latitude will experience more days of heavy rain, defined as more than 0.40 inches. This swath includes Canada,  northern parts of the United States and most of Europe.

• Dry spells, which can lead to drought, could lengthen significantly across the western United States, southern Europe, eastern Brazil and several other areas.

The good news

Not all the news was bad. The model also predicted that the average growing season could increase significantly across most of North America and Eurasia.

Earth’s average temperature has risen by about 1 degree Fahrenheit over the past century. Many scientists blame human activities for the increase and warn that temperatures could rise an additional 2-10 degrees Fahrenheit by the end of the century if steps are not taken to curb carbon dioxide and greenhouse gas emissions.

The study, conducted by researchers at NCAR, Texas Tech University and Australia's Bureau of Meteorology Research Centre, will appear in the December issue of the journal Climate Change.

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