Cooperative Institute for Research in Environmental Sciences Cooperative Institute for Research
in Environmental Sciences

April 8, 2013

First independent confirmation of global land warming

compass.jpgA unique and innovative new observational study that did not use temperature recordings from land stations has confirmed global land warming, according to a scientist at NOAA’s Cooperative Institute for Research in Environmental Sciences (CIRES). The finding refutes concerns that artifacts in land-based observing systems have led to an artificial global land warming trend. 

“This shows that global warming over land is real,” said CIRES scientist lead author Gilbert Compo who works at NOAA’s Earth System Research Laboratory. “It is not an artifact of the observing system. It is happening.”

Since 1952, using a network of weather stations dotted around the globe to take daily readings, scientists have recorded an increase of 1.2 degrees Celsius in Earth’s air temperature over land. Several scientists have, however, questioned the accuracy and representativeness of the land station observations that were used to determine this warming trend, and therefore do not have confidence in it.


Changes in a weather station’s surroundings—such as trees being replaced by concrete—can affect the temperatures recorded at that station. Urban development uses materials that effectively retain more heat than natural cover, leading to a local warming. Similarly, even minor relocation of a weather station can introduce an inconsistency in the recorded temperatures over time, especially if it involves a change in altitude.


Scientists have made corrections to the recorded temperatures to compensate for urban warming and have also corrected several other factors that would cause the observed data to inaccurately represent the true situation. “The question is: Did those corrections work out?” Compo said.

To answer this question and determine whether the observed warming trend is real and accurate, Compo, CIRES Fellow Prashant Sardeshmukh, NOAA scientist Jeff Whitaker and their colleagues used an entirely different approach to investigate land surface temperature trends. The scientists used an approach termed the 20th Century Reanalysis (20CR), a physically based, state-of-the-art data assimilation system (see sidebar) that circumvents the problems faced in using weather station temperature data. 






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, Philip D. Jones from the University of East Anglia, U.K. and the Center of Excellence for Climate Change Research in Saudi Arabia.

Gilbert P. Compo, CIRES,, (303)-497-6115
Jane Palmer, CIRES science writer,, (303)-492-6289