A prominent U.S. skeptic of the human causes of climate change, Richard Muller, has reversed course, saying in a statement released Monday that he now believes greenhouse gases are responsible for global warming.
"I was not expecting this, but as a scientist, I feel it is my duty to let the evidence change my mind," Muller said in his statement.
Muller is part of a group of about a dozen scientists on the Berkeley Earth Surface Temperature team which is studying how temperature changes may relate to human drivers, or to natural events like solar and volcanic activity.
The average temperature of the Earth's land has risen 1.5 degrees Celsius (2.5 degrees Fahrenheit) over the past 250 years, and "the most straightforward explanation for this warming is human greenhouse gas emissions," the team said in a report posted online Monday.
The analysis goes 100 years further back than previous research, and takes an even stronger stance than the UN Intergovernmental Panel on Climate Change which said in 2007 that "most" of the warming of the past 50 years could be attributed to human activity, and that higher solar activity prior to 1956 might have fueled some of the warming the Earth has experienced.
The Berkeley team's analysis said "the contribution of solar activity to global warming is negligible."
It added that its finding does not rely on climate models, which some have criticized for their inaccuracies.
Instead, it is based "simply on the close agreement between the shape of the observed temperature rise and the known greenhouse gas increase."
Further research will factor in ocean temperatures, which are not included in the latest report, it said.
Copyright Agence France-Presse, 2012