New Research Counters Global Warming Skeptics

SEATTLE, Washington, May 7, 2004 (ENS) - A new analysis of satellite data strengthens the scientific consensus that human-caused emissions of greenhouse gases are responsible for global warming. The study finds that temperatures in the lower atmosphere are rising much faster than previously thought - a finding that directly contradicts a primary argument used by global warming skeptics.

The study focuses on the temperature trends in the troposphere, which extends from Earth's surface to an altitude of about 7.5 miles. There is ample evidence that surface temperatures are increasing, but earlier studies had failed to find a similar trend in the troposphere - an information gap seized upon by global warming skeptics.

Climate models predict that such a trend would be present if greenhouse gas emissions are causing the climate to change.

The new study, led by University of Washington atmospheric scientist Qiang Fu, provides evidence that troposphere has been warming faster than the planet's surface and explains why the trend had not previously been shown by satellite data.

The new approach relies on information that Fu says better separates readings of the troposphere from those of another atmospheric layer above, which have disguised the true troposphere temperature trend.

University of Washington atmospheric scientist Qiang Fu. (Photo courtesy University of Washington)

The study appears in the May 6 edition of the journal "Nature."

The team examined measurements from devices called microwave-sounding units on U.S. satellites from January 1979 through December 2001.

Different channels of these devices measure radiation emitted at different frequencies. These readings provide temperature data for different layers of the atmosphere.

The troposphere temperature is measured by channel 2 on the microwave sounding units and the raw data provided no evidence of a warming trend.

But the researchers found those readings were imprecise.

They determined some 20 percent of the channel 2 signal actually comes from a higher atmospheric layer called the stratosphere.

The stratosphere extends upwards from the surface to about 31 miles above the Earth.

Higher amounts of greenhouse gases trap heat near the planet, warming the surface and preventing the heat from reaching the stratosphere.

This factor, combined with ozone depletion, means the stratosphere is cooling about five times faster than the troposphere is warming, Fu said.

"So the channel 2 measurement by itself provided us with little information on the temperature trend in the lower atmosphere," he added.

By using data from weather balloons and from the microwave unit channel dedicated to measuring stratospheric temperatures, the research team developed a method to determine which part of the channel 2 measurement had come from the cooling stratosphere and should be removed.

They used this method to reanalyze data collected between 1979 and 2001, and found that the troposphere's temperature has risen by about 0.2 degrees Celsius (0.4 degrees Fahrenheit) per decade.

Most climate scientists are convinced that greenhouse gas emissions are causing the planet's climate to change. (Photo courtesy NASA)

Fu says one reason previous data have not shown enough warming in the troposphere is because the stratosphere influence on the channel 2 temperature trend has never been properly quantified, even though there have been attempts to account for its influence.

Those attempts had large uncertainties, so many researchers had simply used the unadjusted channel 2 temperature trends to represent the temperature trends in the middle of the troposphere, he said.

"I think everyone can understand our approach," Fu said. "I think this could convince not just scientists but the public as well."

But two leading skeptics are not convinced.

University of Alabama scientists Roy Spencer and John Christy have been at the forefront of past research efforts that showcased the lack of evidence of warming in the troposphere and believe Fu's team has got it wrong.

In an opinion piece published Wednesday in the online publication "Tech Central Station," Spencer said Fu's team overcorrected for the stratospheric impact and he criticized "Nature" for not asking him or Christy to review the paper prior to its publication.

"This is in spite of the fact that we are - arguably - the most qualified people in the field to review [the study]," Spencer wrote. "... the damage has already been done. A paper claiming to falsify our satellite temperature record has been published in the 'peer reviewed' literature, and the resulting news reports will never be taken back."