Astrophysicist Nir Shariv, one of Israel's top young scientists, describes the logic that led him -- and most everyone else -- to conclude that SUVs, coal plants and other things man-made cause global warming.

Step One Scientists for decades have postulated that increases in carbon dioxide and other gases could lead to a greenhouse effect.

Step Two As if on cue, the temperature rose over the course of the 20th century while greenhouse gases proliferated due to human activities.

Step Three No other mechanism explains the warming. Without another candidate, greenhouses gases necessarily became the cause.

Dr. Shariv, a prolific researcher who has made a name for himself assessing the movements of two-billion-year-old meteorites, no longer accepts this logic, or subscribes to these views. He has recanted: "Like many others, I was personally sure that CO2 is the bad culprit in the story of global warming. But after carefully digging into the evidence, I realized that things are far more complicated than the story sold to us by many climate scientists or the stories regurgitated by the media.

"In fact, there is much more than meets the eye."

Dr. Shariv's digging led him to the surprising discovery that there is no concrete evidence -- only speculation -- that man-made greenhouse gases cause global warming. Even research from the Intergovernmental Panel on Climate Change-- the United Nations agency that heads the worldwide effort to combat global warming -- is bereft of anything here inspiring confidence. In fact, according to the IPCC's own findings, man's role is so uncertain that there is a strong possibility that we have been cooling, not warming, the Earth. Unfortunately, our tools are too crude to reveal what man's effect has been in the past, let alone predict how much warming or cooling we might cause in the future.