My friend JR sends me this link, which is as useful a summary of the conventional wisdom regarding global warming as anything. The point being is that there is a strong consensus among scientists (though not a unanimous one*) that global warming is real.
Where a lot of people go wrong is to assume that this is conclusive: we have figured out everything we need, we need to start acting now (JR may believe this himself, if he stops by he can speak for himself). The environmentalist agenda on global warming is much bigger than this. It is fairly summarized in four points:
1. The phenomenon is real and significant.
2. It is caused by human economic activity, mostly excess carbon dioxide released into the atmosphere.
3. If it continues, the consequences will dramatic and adverse.
4. The only solution is immediate radical economic change, primarily by mandating severe worldwide reduction in greenhouse gas emissions.
The "consensus", insofar as it exists, only extends as far as #1 above. (It is also very important to note that just be because there is a scientific consensus behind something doesn't mean that it is true.) The point being, is that all four of these propositions are very highly debatable (and #4 in particular very dubious).
Now by itself, that might not mean anything. Most important decisions are made upon incomplete information. By the time all the relevant information is available, the window for useful action has most likely past. But this is an exception. The sort of thing that would make the environmentalists happy in this case is so radical that we cannot do it haphazardly. It is essentially a worldwide group suicide pact for life as we know it. When you look at a big enough picture, it doesn't matter very much what the nature of our problems are, the nature of the solutions are the same. We as people can only work, create, innovate, perservere, adapt until the problems are gone or at least managed. But that is exactly what the environmentalists want to take away from us. The more religiously motivated among them are doing this on purpose, even.