It's not a question. You can test in a lab how much a certain increase in greenhouse gases change the energy balance and how much heating that causes.
Arguing that we don't know how much man is contributing to global warming is like turning up your thermostat to 78 from 72, and then saying "I don't know how much of the warming was caused by me".
And if the sun rose and radiated heat in through the giant windows during that time wouldn't throw your calculations off?
Look, I'm not a climate scientist so I don't even bother to say I know for sure, all I'm saying is that I've heard it was still an open issue about how much we are contributing last time I checked. If there is a consensus now than fine, my other point still stands though about what to do about it and how to go about it. And like I said before, even if global warming didn't exist I'd still want government to set limits on pollution etc
