Global warming is accelerating at an ever-faster pace, with the past five decades accounting for a whopping 60 percent of the 2.5-degree temperature increase the earth has experienced in the past 250 years.

Calling himself a "converted skeptic" in a recent New York Times guest editorial, physics professor Richard A. Muller said he set out three years ago to wrestle "with problems in previous climate studies that, in my mind, threw doubt on the very existence of global warming."

To do so, he co-founded Berkeley Earth Surface Temperature project with his daughter Elizabeth at the University of California. The research effort involved a dozen scientists, led by Robert Rohde.  It not only measured the worldwide average temperature increase using a wide variety of metrics, but also concluded that human activity is almost entirely responsible for it.

"These findings are stronger than those of the Intergovernmental Panel on Climate Change, the United Nations group that defines the scientific and diplomatic consensus on global warming, Muller said.

"These facts don't prove causality and they shouldn't end skepticism, but they raise the bar: to be considered seriously, an alternative explanation must match the data at least as well as carbon dioxide."