Analyzing temperature data from 15 sources, in some cases going as far back as 1800, a Berkeley Earth study directly addressed scientific concerns raised by skeptics, including the urban heat island effect, poor station quality, and the risk of data selection bias.
On the basis of its analysis, according to Berkeley Earth’s Founder and Scientific Director, Professor Richard A. Muller, the group concluded that earlier studies based on more limited data by teams in the United States and Britain had accurately estimated the extent of land surface warming.
“Our biggest surprise was that the new results agreed so closely with the warming values published previously by other teams in the U.S. and the U.K.,” Muller said. “This confirms that these studies were done carefully and that potential biases identified by climate change skeptics did not seriously affect their conclusions.”
Previous studies, carried out by NOAA, NASA, and the Hadley Center, also found that land warming was approximately 1°C since the mid-1950s, and that the urban heat island effect and poor station quality did not bias the results. But their findings were criticized by skeptics who worried that they relied on ad-hoc techniques that meant that the findings could not be duplicated. Robert Rohde, Lead Scientist for Berkeley Earth, noted that “the Berkeley Earth analysis is the first study to address the issue of data selection bias, by using nearly all of the available data, which includes about 5 times as many station locations as were reviewed by prior groups.”
Elizabeth Muller, Co-founder and Executive Director of Berkeley Earth, said she hopes the Berkeley Earth findings will help “cool the debate over global warming by addressing many of the valid concerns of the skeptics in a clear and rigorous way.” This will be especially important in the run-up to the COP17 meeting in Durban, South Africa, later this year, where participants will discuss targets for reducing Greenhouse Gas (GHG) emissions for the next commitment period as well as issues such as financing, technology transfer and cooperative action.
The Berkeley Earth team includes physicists, climatologists, and statisticians from California, Oregon, and Georgia. Rohde led the development of a new statistical approach and what Richard Muller called “the Herculean labor” of merging the data sets. One member of the group, Saul Perlmutter, was recently announced as a winner of the 2011 Nobel Prize in Physics (for his work in cosmology).
The Berkeley Earth study did not assess temperature changes in the oceans, which according to the Intergovernmental Panel on Climate Change (IPCC) have not warmed as much as land. When averaged in, they reduce the global surface temperature rise over the past 50 years – the period during which the human effect on temperatures is discernable – to about two thirds of one degree Centigrade.
Specifically, the Berkeley Earth study concludes that:
