Suppose the weather is indeed changing. It does not matter whether this is caused by man or not. And one does not need to wait to have irrefutable evidence to start acting.
People build computer models to simulate the weather. The physics is not the problem. The initial conditions and the assumptions are the problem. The atmosphere is vast. We can measure temperature and other stuff mostly at the Earth's surface. Some people are now building UAVs to fly around and collect measurements which will be used to increase the accuracy of the climate models. One problem: the climate is a chaotic system, i.e., it's highly sensitive to disturbances on initial conditions. Another problem: the models neglect the biosphere. Most carbon is in the biosphere, not in the atmosphere. Computer model says temperatures are going to increase 9 degrees Celsius. People panic. Wait. Does anyone know how to model the dynamics of the biosphere?! Short answer: no. It's a complicated problem. You can forecast CO2 emissions from industry, but no one has a clue how the biosphere will react to abrupt temperature variations.
One caveat: there are cycles. The Sun has cycles. The Earth also has cycles. The temperature in the middle ages was known to be a few degrees higher. Was it also due to CO2 emissions from the industry? Definitely not.
There was a time when there was no ice on the Arctic. There was also a time when most coastal areas we have today were underwater. There's no reason why that can't happen again, for sure.
An important issue: what does "global warming" even mean? Are the minimum / median / average / maximum temperatures increasing? Or is the variance increasing? Does this happen everywhere. What I read was that the cold, high-latitude regions were getting "warmer" (whatever that means), while the tropical regions were pretty much the same. This is too much complexity to be sold to the masses. The masses want entertainment, not information.
OK, suppose that temperature will increase by 9 degrees or so. Sea levels will rise and threaten us all. The U.S. can try to regulate emissions to counter this, but will the Chinese do the same? This is Game Theory 101. Moreover, what will people in the U.S. and Europe say:
"Sorry you Chinese, Indians and Brazilians. We destroyed the planet, and now we won't allow you to develop because of that. If you want to keep your houses warm in the winter and power your industry, we will accuse you of treason."
Last but not least: is regulation the best solution? What is the problem with global warming exactly? Rising sea levels? Increased CO2 concentration is good for the plants because they grow faster. I say, build a pipeline from the Arctic to the Sahara to pump fresh water into local agriculture. If the Israelis can grow tomatoes in the Negev desert, I don't see why the North Africans can't do the same.
The problem with regulation is that it won't work on a global scale. A politician would rather compromise the planet than tell his own people that they have to starve and freeze to reduce emissions. This is much more than capitalist greed. This is about human rights: people should have the right to consume energy to increase their standard of living.
Science is one thing. Policy is another. Let us keep them separate. Studying the climate should be decoupled from politics as much as possible.