Scientists correct errors in climate data
The computer models of most climate scientists predict global warming. But the air over the tropics didn't seem to be warming as much as the models predicted. The latest study by Mears and Wentz -- reported in Sciencexpress on August 11, 2005 -- shows that an error in measuring temperatures in the tropics may have caused the discrepancy, thereby strengthening the validity of the models. Above, a global map showing averages of temperature trends from the Mears/Wentz study (1979-2003).
JB: This is Earth and Sky. Climate scientists agree that Earth’s surface is warming. According to computer simulations, the air just above Earth’s surface should also be warming.
DB: But, until recently, satellite measurements seemed to indicate that the lower atmosphere over the tropics wasn’t warming. Now, researchers at Remote Sensing Systems in California report errors in the way climate scientists have analyzed the satellite data. One error resulted from the fact that the satellites’ orbits have drifted over time so that they passed over the same spot a little later each day. Add that to the fact the air temperatures naturally vary throughout the day.
JB: According to the new study, if that effect is correctly taken into account, then in recent decades, the air over the tropics appears to be warming at a rate of about 2 degrees Celsius per century. Some critics still disagree. They say the atmospheric warming in the tropics isn’t as large as predicted by computer models. But Carl Mears – co-author of the recent paper – is encouraged by the fact that the gap between predictions and observations has shrunk.
Carl Mears: It improves our confidence in the models. No longer can you say these models are flawed because they can’t even get the trends in the tropical troposphere correct. . . . There’s no longer a strong argument saying that the models are wrong.
DB: Thanks today to NOAA – the National Oceanic and Atmospheric Administration. We’re Block and Byrd for Earth and Sky.
Climate scientists use computer models to predict how Earth’s climate might change in the future. To test the models, they run them backwards in time and see how well they match historical records of Earth’s real climate.
Until recently, climate scientists were puzzled by one nagging detail. Yes, Earth’s surface appeared to be warming in the models and in the real world. But the atmosphere was a different story. For example, the air over the tropics didn’t seem to be warming as much as climate models predicted they should. Some climate scientists said the models must be wrong and if the models are wrong, then they can’t be trusted to give accurate predictions of Earth’s climate decades from now. But the latest study by Mears and Wentz – reported in the online journal Sciencexpress on August 11, 2005 – helps resolve this dilemma.
Mears says that the satellites that measure the temperature of the atmosphere have slowed down over time. So if a satellite used to pass over the equator at say 2pm, it might now pass over at 5pm.
Mears said, “And most people can tell you that if you go out at 5pm, it’s often cooler than it was at 2pm. So if you didn’t take that into account, then there would be an artificial cooling trend in your measurements and it would look like maybe you had global cooling, when in fact, you had global warming.”
This drift was accounted for in earlier analyses by other scientists – but they still didn’t correct the data enough. That’s because the satellites may also be wobbling. So another correction had to be made.
Read about the recent study from RSS and two other related papers that were published in conjunction with it in Sciencexpress.
Read John Christy’s response to the new papers. Christy is a climate researcher at the University of Alabama at Huntsville. He is often portrayed as a climate change skeptic; but to be fair, he maintains that his focus is on collecting and analyzing climate data without a bias toward the results.
Our thanks to:
Carl Mears
Remote Sensing Systems
Santa Rosa, CA
John Christy
Professor and Director
Earth System Science Center, NSSTC
University of Alabama in Huntsville
Huntsville, AL
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