Is climate change real? Has the planet been warming? Are human activities contributing to the harm? Can we predict with certainty the worst consequences, and how quickly they will occur?

The answers to these questions, based on several decades of peer-reviewed research, are "yes" on the first three, and "no" on the fourth.

There's broad scientific agreement on the planet's thermostat: Average temperatures increased significantly in the final decades of the last century. There's also broad agreement – not universal – that a buildup of greenhouse gases, largely from the burning of fossil fuels, has contributed to this rise.

But the debate isn't over. Climate scientists are not soothsayers. They cannot predict the future any better than, say, economists. Thus, there is intense scientific debate about how quickly glaciers and land-based ice sheets will melt and sea levels will rise, and how quickly other fearsome impacts – catastrophic floods, droughts and extinctions – could occur.

For members of the public, the trick is to understand the real points of debate. That means separating consensus from misrepresentations put forth by groups on the fringe. These include "climatistas" – environmental activists who hype the worst possible outcomes. But more often they are the "contras" – deniers of climate change who recklessly want to cling to the status quo.

In Copenhagen, Denmark, today, leaders from around the world will meet to discuss next steps on addressing this planetary threat. With countries such as China and India showing a willingness to reduce emissions, it could set the stage for a truly international effort to pursue cleaner energy policies.

Sadly, much of the world's media may remain focused on the release of thousands of embarrassing e-mails hacked (stolen) from a climate research institute in England. These e-mails reveal the shocking fact that, within academia, individual researchers can act badly and harbor biases that exclude others.

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