It doesn't matter. What matters is what are the implications of the changes suggested in the agreements like the Paris agreement. They can be disastrous economically with little to no effect on the climate.
It is very real. But even if it turns out not to be real, are you willing to gamble the entire Earth? You take out insurance on your home not because you think that your house is going to flood or burn down, but because you want to be safe even though the chances are slim. We should have the same mentality when it comes to climate change. It would better to act now and learn down the road that climate change does not exist than to continue doing nothing and have it turn out that climate change is real.