Gilbert Compo and coauthors confirm warming: 20th Century Reanalysis Project uses barometric pressure, ocean surface temperature

CU-Boulder-led study confirms warming, without thermometers

by Charlie Brennan, Camera Staff Writer, April 11, 2013  
A reconstruction through historical data of the destructive 1900 hurricane in Galveston, Texas. The data is based on the 20th Century Reanalysis Project, which has been used to verify global warming in a new study. (Courtesy: NOAA) 

The affiliations of co-authors to this study have been updated to correct earlier information taken from a press release.

The thermometers got it right. The Earth is warming, another study is reporting.

Climate scientists recognize that changes in weather observation stations' immediate surroundings -- such as neighboring trees being replaced by heat-absorbing concrete -- can eventually throw data from such stations into question.

But now, a new study directed by a researcher at the National Oceanic and Atmospheric Administration that recreates climate history without the use of land-based observation systems shows the same thing that thermometers have been reporting.

"This shows that global warming over land is real," said Gilbert Compo, a scientist at NOAA's Cooperative Institute for Research in Environmental Sciences at the University of Colorado.

"It is not an artifact of the observing system," said Compo, lead author of the study, which he presented to the European Geophysical Union on Tuesday in Vienna. "It is happening."

Compo and his colleagues used an alternate method to review the planet's temperature history from 1871 through 2010.

They deployed what is called 20th Century Reanalysis (20CR), a physically based, state-of-the-art data assimilation system using barometric pressure records, ocean surface temperatures and other factors independent of land-based readings that can be skewed by changes in their surroundings.

Compo's team came to a conclusion that supports land-based instruments' reporting that, since 1952, the Earth has shown a 1.18 degree Celsius increase in air temperature over land.

Compo, in an email, stated that the actual number the 20CR analysis showed for warming since 1952 was 0.78 C, which he termed "statistically indistinguishable" from 1.18 C.

Also, the study showed an increase from 1901 to 2010 of 0.99 C, which Compo said "is larger than some (land-based) instrument datasets, while smaller than others -- and is statistically indistinguishable from all of them."

NOAA meteorologist Jeffrey Whitaker, a co-author of the study, explained why some land-based historical readings have come not to be trusted.

"With weather stations that were in rural areas in the early part of the 20th century, you have cities that grow up around them, and they look like they have a (warming) trend, but part of that trend could be because a city grew up around them. It could have nothing to do with a global warming signal, per se.

"But urbanization and land-use changes wouldn't affect our analysis because we didn't use any of that information," Whitaker added. "All we used were the barometers and the temperatures over the ocean."

"One thing we found was that the barometer is even more valuable than we thought," Compo said. "We were able to reproduce the hour-by-hour, day-by-day variations in temperature using only barometric pressure as a starting point."

Whitaker is not anticipating that the study, published Monday in Geophysical Research Letters, will suddenly turn around global warming skeptics.

"This doesn't really change the answer," Whitaker said. "This is just one extra piece of evidence. It is not enough that I think it is really going to sway anybody's mind who isn't already convinced, one way or the other."

But Compo expressed hope "that the general public and decision makers, no matter what their political affiliation, would recognize that the warming of the land areas is real. Even the barometers can tell that the planet is warming."

Other co-authors of the project are CIRES scientists Prashant D. Sardeshmukh and Chesley McColl, Philip Brohan at the Met Office Hadley Center in the United Kingdom, and Philip D. Jones from the University of East Anglia, U.K., and the Center of Excellence for Climate Change Research in Saudi Arabia.

Contact Camera Staff Writer Charlie Brennan at 303-473-1327 or brennanc@dailycamera.com.