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June 2, 2004
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  Global Warming    

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Global Warming

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A group of scientists have published information they say strengthens the case for global warming. As this ScienCentral News video reports, the study, published in the journal "Nature," investigates a scientific puzzle about temperature change.

Warming Trend

Global warming refers to an average increase in the Earth's temperature, and our planet does seem to have warmed by about 1 degree Fahrenheit over the past century, with accelerated warming during the past two decades.

But there's a scientific riddle that skeptics of global warming have used to cast doubt on computer forecasts predicting this warming trend: Temperatures are indeed rising near the earth's surface, but, up in the lower atmosphere, or troposphere, where the most weather occurs, measurements have shown comparably small increases.

"There was a long debate in the science community about the temperature trends in the atmosphere and at the surface," says Qiang Fu, an atmospheric physicist at the University of Washington. "Based on the surface records, the surface temperature change has increased tremendously, [but] in the lower atmosphere based on satellite observations, the lower atmosphere hasn't changed as much as the surface. In a lot of ways, the global climate model tells us these two have to be increasing at the same time."

So Fu and his team re-examined the information from NOAA satellites carrying devices called microwave-sounding units. The units measure microwave energy to determine temperatures at various levels in the atmosphere. "I think the basic question we want to answer in the research is what's the temperature trend in the lower atmosphere," Fu says. "That is, how has the temperature changed in the last 20 years in the lower atmosphere, based on the satellite measurements."

Scientists measure temperatures in the troposphere by looking at the microwave energy given off by oxygen. The energy is measured across several frequency ranges called channels. One range, channel 2, mostly measures the troposphere, but it also measures part of the upper atmosphere, known as the stratosphere, which, according to Fu, cools about five times faster than the troposphere warms, due to ozone depletion and the increase of greenhouse gases.

Fu and his team wanted to somehow remove the extra information from the readings, so they moved to another frequency, known as channel 4, which measures just the stratosphere. By comparing channel 4 to channel 2, they could then subtract out the interference from the stratosphere to come up with more accurate temperatures about the troposphere.

After examining measurements from January 1977 through December 2001, Fu and his team found the rising temperatures were indeed much closer to what the computers predicted—the troposphere has been warming at about one-third of a degree Fahrenheit per decade, which closely resembles measurements of warming at the surface. "So that means at least that people shouldn't use [previous figures]...as a basis to say global warming does not happen," says Fu. "I hope that convinces people that global warming does happen, not only at the surface, but also in the atmosphere."

Fu hopes this new information will allow researchers to move forward and focus on other issues regarding climate change. This research was published in the May 6, 2004 issue of the journal Nature. It was funded by the U.S Department of Energy, the National Science Foundation, and NASA.

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