Global warming is happening and “humans are almost entirely the cause.” That’s the conclusion reached by a team of researchers at UC Berkeley, led by professor Richard Muller, who now considers himself a “converted skeptic” on the issue.

The study, conducted by the Berkeley Earth Surface Temperature project (BEST), found that the average temperature of the Earth’s land rose by 2.5 degrees Fahrenheit over the past 250 years, including a 1.5 degree increase in the most recent 50 years. Perhaps most important, researchers found that warming could increase by another 1.5 degrees in as little as 20 years if rapid industrial growth in developing countries continues.

Solar and volcanic activity — two potential causes of warming often cited by global warming deniers — were found to have negligible impacts on temperature at the surface of the Earth compared with greenhouse gases.

“We were not expecting this, but as scientists, it is our duty to let the evidence change our minds,” Muller said.

“Much to my surprise, by far the best match came to the record of atmospheric carbon dioxide, measured from atmospheric samples and air trapped in polar ice. … While this doesn’t prove that global warming is caused by human greenhouse gases, it is currently the best explanation we have found, and sets the bar for alternative explanations.”

— Posted by Alexander Reed Kelly.