It has become very difficult for anyone to argue that observed global warming is natural variability. We have good reason for being able to say that the world will be warmer by about a quarter of a degree in the next decade. It's the same reason we had 10 years ago when we said that the 1990s would be warmer than the 1980s: The planet is out of equilibrium.

Imagine a giant asteroid on a direct collision course with Earth. That is the equivalent of what we face now with climate change, yet we dither.

...99 percent confident that the world really was getting warmer and that there was a high degree of probability that it was due to human-made greenhouse gases.

Our analysis shows that, for the extreme hot weather of the recent past, there is virtually no explanation other than climate change. The deadly European heat wave of 2003, the fiery Russian heat wave of 2010 and catastrophic droughts in Texas and Oklahoma last year [2011] can each be attributed to climate change. The odds that natural variability created these extremes are minuscule, vanishingly small. To count on those odds would be like quitting your job and playing the lottery every morning to pay the bills.

The trains carrying coal to power plants are death trains. Coal-fired power plants are factories of death.

Only in the last few years did the science crystallize, revealing the urgency - our planet really is in peril. If we do not change course soon, we will hand our children a situation that is out of their control.

The last time the world was three degrees warmer than today-which is what we expect later this century-sea levels were 25m higher. So that is what we can look forward to if we don't act soon.