Satellites' Accuracy Challenged
For nearly a decade, climate-change critics have pointed to a single discrepancy to prove global warming isn't real: satellite measurements of the atmosphere's temperature.
Now, a new analysis of satellite-based temperatures has thrown doubt onto their decade-old conclusion that Earth's atmosphere isn't warming.
The inquiry, by a Santa Rosa company, shows significant warming of the upper atmosphere. The temperature rise is nine times larger than shown in previous studies and meshes more closely with other global-warming findings, like melting glaciers, warming oceans and, perhaps most importantly, computer models of global climate.
Resolving this "very troubling disagreement" between computer climate models and the satellite data is vital because scientists use real-world data to test if their models are accurate, said Thomas Crowley, a Duke University professor. Those models give local and regional planners and policy makers insight into what might happen if warming isn't slowed.
This new analysis shows "it may not be a real model problem," Crowley said. "It may be a data problem.
"It takes a significant impediment to reconciling models and observations and removes it," he said.
In a study published this year in Science magazine, Lawrence Livermore Laboratory's Ben Santer and his colleagues looked at how immense computer climate models compared with the new Santa Rosa data and the first-ever analysis of the satellite temperature data, done a decade ago by scientists at the University of Alabama in Huntsville. They found even a small difference, about .08 degrees per decade, makes a big difference for those evaluating climate models.
"These uncertainties matter," Santer said. "Comparing climate models with observations matters."
For years, scientists have seen satellites as an attractive way to measure warming.
Unlike earth-bound thermometers or weather balloons, they can measure temperatures on the planet's whole surface. They are one of only a few ways scientists can look at the upper atmosphere, a vital part of global warming models.
For that reason, satellite data has been the last stronghold for climate change critics who have pointed to flat temperatures, found by the Huntsville researchers, as proof global warming isn't real. They used that criticism to cast doubt on many climate change measurements, from surface temperatures to ocean warming to computer climate models.
But satellites have problems that make some observers skeptical of their usefulness.
These satellites are "a very blunt probe for observing climate change," said Graeme Stephens at Colorado State University. "It is like looking for the SARS virus in a microscope that is totally out of focus. You can see a little something, but that is all you can really say."
The satellites weren't designed to find global warming, but for daily weather forecasting.
They drift both up and down and side to side in their orbits over the earth. There have been 10 different satellites; all measure temperature slightly differently.
Satellites do not directly measure temperature but look at microwaves emitted by oxygen molecules scattered fairly evenly throughout the atmosphere.
Those problems require people who turn satellite data into global-warming numbers to make dozens of small corrections, each with its own uncertainty.
"If you didn't do any corrections, you would end up with gobbledygook," said Frank Wentz, director of Remote Sensing Systems, the Santa Rosa company that did the new analysis. "The best way to hedge against that is to have competitive groups."
Until now, only the Huntsville group, led by John Christy, had analyzed the satellite data. That group consistently found almost no warming in satellite data beginning in 1979. Using different corrections for the same data, the Santa Rosa group found more significant warming.
"How you glue (the data) together becomes very important if you want to say something about how temperatures have changed over long periods of time," said Jim Hurrell, a senior scientist at the National Center for Atmospheric Research in Boulder, Colo.
Both groups stand behind their calculations.
"I don't see anything there that I would change about ours," Christy said.
But both groups agree that some climate predictions are more extreme than either has found.
"Even with our warmer trend, we are not seeing the really serious global warming people are talking about," Wentz said.
Not surprisingly, the Santa Rosa and Lawrence Livermore studies have been bashed in online chat rooms by noted global-warming critics.
But others say it is vital to have a second study because, if nothing else, it shows the findings are more uncertain than previously thought.
"This is more or less an indication of how uncertain these measurements are," Stephens said.
Observers hope the controversy will draw more people into the field so a consensus emerges on whether the satellites show warming. Crowley said he thinks the prestigious National Academy of Sciences should take up the question.
"This is nominally the best observed period in the earth's history," Santer said.
"My gut feeling is that we may never be able to resolve this issue. We can't go back in time and make the observing system better."
source: http://www.bayarea.com/mld/cctimes/content_syndication/local_news/6053571.htm 11jun03
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