for National Geographic News
A study conducted by scientists in the U.S. and Italy warns that summers could be a lot hotter in a hundred years because of global warming caused by greenhouse gases.
"Summer is likely to be more severely hot everywhere in the U.S.," said Noah Diffenbaugh, an atmospheric scientist at Purdue University who co-authored study.
"In the Southwest, if you imagine the hottest two and a half weeks of the year, you're looking at that becoming three months long. Phoenix [Arizona] will get three months of what is now the hottest two weeks of the year."
Winter weather could be affected as well, Diffenbaugh said. "You're looking at the coldest couple of weeks of the year not existing anymore in lot of places," he said.
"Certainly winter as we know it likely will disappear in the Northeast."
Although there are several types of greenhouse gases in the Earth's atmosphere, an abundance of carbon dioxide is thought to be the prime cause of the greenhouse effect that prevents heat from escaping the Earth.
Many scientists think the effects of human activitysuch as automobile emissionshave increased carbon dioxide levels and are causing global warming.
The results of the study are detailed in an article co-authored by researchers at Purdue and the Abdus Salarn International Centre for Theoretical Physics in Trieste, Italy.
The study was conducted with computer simulations using climate data and projections of greenhouse gas levels.
The results appear in today's online edition of the Proceedings of the National Academy of Sciences.
Warming Has Started
The study notes that during the late 20th century the U.S. experienced "more hot events, more heavy precipitation events, and fewer cold events."
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