How will we know if 2010 was the warmest year on record?
How? In a story just published at Climate Central, I answer that question, explaining how different groups of scientists using much the same data come up with independent assessments of the Earth’s changing temperature. Keep reading for the first part of that article. Then click on the link at the bottom of this post to head over to Climate Central for the rest of the story . . .
Earlier this month, NASA’s Goddard Institute for Space Studies (GISS) announced that November was the warmest such month in its record books — and that 2010 overall may well turn out to be the warmest year ever.
Now, the National Climatic Data Center (NCDC), part of the National Oceanic and Atmospheric Administration (NOAA), has published the results of its own calculations, showing that November was thesecond warmest, not the first.
Such conflicts in global temperature rankings aren’t terribly unusual. In fact, NASA-GISS and NOAA-NCDC rank 2005 as the warmest year on record. But a third group, a collaboration of the U.K. Met Office’s Hadley Center and the Climatic Research Unit known as “HadCRUT,” gives the title to 1998. (When December hits the record books, it’s possible that 2010 will be crowned warmest year by all three.)
Each of the three groups calculates temperatures at the surface of the land and sea. But two other groups, one at the University of Alabama and the other at Remote Systems Sensing, use microwave sensors on satellites to estimate the temperature of the lowest part of the atmosphere.
And guess what? Their findings differ a bit from each other, and from those of the other groups as well.
What’s going on here? And do these discrepancies cast doubt on the conclusion that the world is warming?
What’s going on is quite simple, scientists say: normal science. The groups come up with somewhat different results because each one approaches the complex task of determining global temperature trends in a different way.
Perhaps it’s not surprising that the two satellite records tend to differ from the others — because they use a completely different technology and analytical method. Their approach tends to exaggerate the impact of ocean-atmosphere phenomena like El Niño (which causes warming) and volcanic eruptions (which cause cooling).
But it may be less obvious why the three groups that use much the same basic surface temperature data still diverge in their findings.
“Each group tries to do the best job possible,” says Richard Reynolds, a scientist with NOAA, now semi-retired, who helped refine that agency’s approach. “Different decisions on the data processing cause the final numbers to differ. However, the differences are very useful to help define the uncertainty in the results.”
Despite those uncertainties, a consistent picture has emerged: Since 1970, each decade has been warmer than the one before — and 2000 to 2010 has been the warmest one on record.
Map of global average temperature anomalies from 2000-2009, showing the most rapid warming in the Arctic and a small portion of Antarctica. Credit: NASA Earth Observatory.
Of course, the subject of global temperature trends has become intensely politicized. This has been especially true in the aftermath of the controversy surrounding the unauthorized release of hundreds of email messages between some climate scientists, including Phil Jones, director of the Climatic Research Unit.
To many climate change skeptics, the emails suggested that Jones and his colleagues at the CRU deliberately manipulated data to concoct a global warming trend, and also stonewalled critics, preventing them from accessing CRU data.
Since then, an independent review, headed by Sir Muir Russell, found that while CRU scientists failed to show the appropriate degree of openness, the accusations of fabrication, dishonesty and lack of rigor were groundless. Other reviews also found accusations of data-rigging to be groundless. And there is now a move afoot to make surface temperature data much more easily accessible.
Even so, some public doubt remains about assessments of global temperature trends. A Yale Universitysurvey found, for example, that 40 percent of Americans still believe there is significant disagreement among scientists over whether global warming is occurring.
Gavin Schmidt, a scientist with the NASA-GISS team, argues that even though they differ somewhat, the independent assessments of Earth’s temperature trends “are exactly what is needed to reassure people. The differences reflect real uncertainties,” he says, “but the similarity in the bottom line, despite variations in approach, should increase credibility in the overall warming trend.”
To understand why different answers to the same question can be perfectly normal from a scientific perspective — and how they all actually add up to the same overall trend — it helps to know how the different groups go about their work.
To read the rest of this post, please check out the entire story over at Climate Central.