"Global warming is real," a team of scientists at the University of California at Berkeley said Friday. Since the 1950s, the earth has warmed about 1° C.
Last year, Richard Muller and a team of colleagues, including Saul Perlmutter, 2011 Nobel Prize winner in physics, started the Berkeley Earth Surface Temperature study to review and assess the accuracy of existing land temperature data. The team looked at temperature data from 15 previous studies—amounting to some 1.6 billion combined records dating back to 1800—on the subject.
Muller says that concerns raised by global warming skeptics were specifically addressed, including the urban heat island effect, poor station quality, and data selection bias. The group's results aligned closely with previous studies' findings, including ones carried out by groups such as NASA, the Hadley Center, and the National Oceanic and Atmospheric Administration.
"Our biggest surprise was that the new results agreed so closely with the warming values published previously," Muller said in a statement. "This confirms that these studies were done carefully and that potential biases identified by climate change skeptics did not seriously affect their conclusions."
The group analyzed almost all existing data on the topic, looking at climate data from approximately five times more temperature stations than previous studies used. The group released four scientific papers for peer review that they will present at the next Intergovernmental Panel on Climate Change.
Muller and his daughter, Elizabeth, who co-founded the project, said they hope the study will help silence skeptics. Elizabeth Muller said she hopes their findings will "cool the debate over global warming by addressing many of the valid concerns of the skeptics in a clear and rigorous way."
Those concerns include pointing at the urban heat island effect (a theory that because urban areas have higher land temperatures, ground temperature data from those areas artificially raise global land temperature averages), unreliable temperature stations (Anthony Watts, a meteorologist who studies weather stations, found that many temperature-reading stations deemed to be of poor quality actually have a slight cooling bias), and the fact that a large number of stations have recorded global cooling over the past 70 years.
The study concluded that although the urban heat island effect is real, it does not contribute much to global land temperature rises because urban areas make up less than one percent of total land area. The scientists found that one third of stations reported global cooling, but two thirds show global warming.
"A good determination of the rise in global land temperatures can't be done with just a few stations: it takes hundreds—or better, thousands—of stations to detect and measure the average warming," lead scientist Robert Rohde said in a statement.
The team measured only land temperature data—global ocean temperatures are thought to have warmed less. The team plans on tackling that project next.