LIVERMORE, Calif. -- Though most scientists agree that global warming is real and occurring as we speak, a few pieces of the puzzle have proved difficult to fit into place.
Critics of the warming theory have clung to these last bits of evidence, but new research at Lawrence Livermore Laboratory is hammering another nail in the naysayers' coffin.
Most climate models predict that loading the atmosphere with carbon dioxide and other greenhouse gases, as humans have done for more than 150 years, should warm the troposphere -- the lowest layer of atmosphere -- faster than the planet's surface. But temperature measurements from weather balloons and satellites show that while the surface has warmed, the troposphere has warmed more slowly and actually cooled slightly in some places since 1979.
''The skeptics have always used this as one of the arguments that climate scientists don't know what they're talking about and global warming isn't real," said climatologist John Chiang of the University of California, Berkeley.
Now, two groups of scientists have corrected errors in the temperature data, revealing that the troposphere has indeed warmed faster than the surface.
To follow up, atmospheric scientist Ben Santer of Lawrence Livermore led a team of 25 scientists that found the corrected temperature data agree with 19 different computer climate models from around the world. The three studies were published yesterday in the journal Science. ''We hope that these three papers together will advance the debate, if not end it," said Santer.
Climate models predict that the difference between the temperature at the surface and that of the troposphere would be greatest in the tropics where warm moist air rises and then releases heat as it condenses into clouds. But the temperature data were showing a slight cooling of the tropical troposphere.
So either the climate models were wrong, or the temperature data were wrong, Santer said.
Measuring long-term temperature trends from satellite data is tricky because satellites drift a little bit in their orbit over time. This means that the time of day when a particular satellite is measuring temperature in a specific location can change by several hours over the course of a few years.
Only one scientific team, from the University of Alabama, had attempted the difficult process of correcting the satellite data to take orbital drift into account until now.
Carl Mears and Frank Wentz of Remote Sensing Systems in Santa Rosa, Calif., found a problem in the Alabama team's correction. When Mears and Wentz reprocessed the temperature data with a new, improved orbital correction, they found that the troposphere had indeed warmed instead of cooled.
Researchers at Yale University tackled the weather balloon record and found problems there, too. When the problems were fixed, that record showed warming as well.
''Both of them now show convincing evidence that the troposphere has warmed," Santer said.
The new data fit nicely with the models, particularly in the problematic tropics where the extra warming of the atmosphere is greatest. ''This study is significant because it removes one of the arguments that the climate skeptics have used," said Chiang.
Santer hopes his results will help move the climate change debate forward. ''Most reasonable scientists believe that we know enough now, that we've found strong causal links between human activity and the global warming we've already experienced," he said.