Compo et al., 2013 – Click the pic to view at source

Image Credit: Compo et al., 2013

From the Huffington Post:

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 degrees Celsius, which he termed “statistically indistinguishable” from 1.18 degrees Celsius.
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Here’s the associated study; Independent Confirmation of Global Land Warming without the Use of Station Temperatures and abstract.

I’ll leave it to WUWT’s readers to do their own distinguishing…