They pledged net zero emissions by 2050. Also if the science about it was fake they would have the most incentive to call it out.
Discussion
Is that by purchasing carbon offsets?
No. Their plans do look a bit sketchy though. Planting trees and unproven carbon capture tech seems to be a big part of the plan, and there are no plans to scale back fossil fuels. Even if they aren't that committed I still think if the science was wrong they would be fighting against it rather than playing along.