It is impossible to prove that climate change will occur and is man made. The only way to do that would be to do the experiment: find a planet, pump lots of C02

It is impossible to prove that climate change will occur and is man made. The only way to do that would be to do the experiment: find a planet, pump lots of C02 into its atmosphere and measure the result. Of course you would have to do this a number of times with different planets using some as controls. However science can estimate from small scale experiments and theoretical calculations a probability that global warming is man-made and its likely effects. Even if the probability of a catastrophe is small, say 5%, it is still worth spending a small percent of GDP to prevent or to ameliorate it. It's like if you own a house you would be an idiot not to spend good money on fire insurance even though the probability of your house burning down is very small.