The study from the Berkeley Earth Surface Temperature Project found an increase of land temperature by about 1C since the 1950s, results that researchers believe should silence skeptics. (Image via creative commons, credit NASA)

In the most comprehensive study of historical temperature records to date, an independent investigation led by researchers at the University of California, Berkeley said Friday global warming is real.

The researchers in the study say skeptics no longer have a basis for denial of global warming, as a list of more than a billion records from 15 sources dating back to the 1800s was complied in support of the study.

From The State Column:

The researchers calculated the average global land temperature has risen by around 1C since the mid-1950s. These calculations agree with previous estimates from major groups that maintain official records on the world’s climate. These groups include NASA’s Goddard Institute for Space Studies in New York, the U.S. National Oceanic and Atmospheric Administration (NOAA), and the Met Office’s Hadley Centre, with the University of East Anglia, in the UK.

According to the study, the accuracy of the findings as well as those of previous studies were unaffected from previous criticisms of poor quality of the temperature stations often used to take readings.

The chairman of the research team, Richard A, Muller, wrote in a letter to the Wall Street Journal:

Again, our statistical methods allowed us to analyze the U.S. temperature record separately for stations with good or acceptable rankings, and those with poor rankings (the U.S. is the only place in the world that ranks its temperature stations). Remarkably, the poorly ranked stations showed no greater temperature increases than the better ones. The mostly likely explanation is that while low-quality stations may give incorrect absolute temperatures, they still accurately track temperature changes.

Researchers in the study also say the criticism that results are skewed by the urban heat island effect (a phenomena that causes asphalt-filled cities to absorb more heat than rural areas) did not affect measurements, because urban areas only take up about one percent of the Earth's surface.

Muller said that the study did not make an independent assessment of how much global warming is man-made, but also said he hopes the findings can help settle arguments over the topic as a whole.

The project was organized by the Santa Barbara-based non-profit organization Novim, and received funding from the Fund for Innovative Climate and Energy Research and the Department of Energy’s Lawrence Berkeley Lab.

Reach reporter Shea Huffman by email, or follow him on Twitter.