A 2002 study by the U.S. National Academy of Sciences warned, "Abrupt climate changes were especially common when the climate system was being forced to change most rapidly." The rapidly growing greenhouse warming we ourselves are causing today thus increases the chances for "large, abrupt and unwelcome regional or global climatic events."

Over and over again, scientists have demonstrated that observed changes in the climate in recent decades can only be explained by taking into account the observed combination of human and natural forcings. Natural forcings alone just don't explain what is happening to this planet.

For instance, in April 2005, one of the nation's top climate scientists, NASA's James Hansen, led a team of scientists that made "precise measurements of increasing ocean heat content over the past 10 years," which revealed that the Earth is absorbing far more heat than it is emitting to space, confirming what earlier computer models had shown about warming. Hansen called this energy imbalance the "smoking gun" of climate change, and said, "There can no longer be genuine doubt that human-made gases are the dominant cause of observed warming."

Another 2005 study, led by the Scripps Institution of Oceanography, compared actual ocean temperature data from the surface down to hundreds of meters (in the Atlantic, Pacific and Indian oceans) with climate models and concluded:

A warming signal has penetrated into the world's oceans over the past 40 years. The signal is complex, with a vertical structure that varies widely by ocean; it cannot be explained by natural internal climate variability or solar and volcanic forcing, but is well simulated by two anthropogenically forced climate models. We conclude that it is of human origin, a conclusion robust to observational sampling and model differences.

Such studies are also done for many other observations: land-based temperature rise, atmospheric temperature rise, sea level rise, arctic ice melt, inland glacier melt, Greeland and Antarctic ice sheet melt, expansion of the tropics (desertification) and changes in precipitation. Studies compare every testable prediction from climate change theory and models (and suggested by paleoclimate research) to actual observations.

The paleoclimate record shouts out to us that, far from being self-stabilizing, the Earth's climate system is an ornery beast which overreacts even to small nudges.

That is, you need a trigger to start the process of rapid climate change. Historically, that has been orbital changes, or sometimes, massive natural releases of greenhouse gases.

Now humans have interrupted and overwhelmed the natural process of climate change. Thanks to humans, carbon dioxide levels are higher than they have been for millions of years. Even more worrisome, carbon dioxide emissions are rising 200 times faster than at any time in the last 650,000 years.

If the "Earth's climate system is an ornery beast which overreacts to even small nudges," what will happen to people foolish enough to keep punching it in the face?