Think of it this way: it’s impossible due to quantum uncertainty to predict the path of a single particle in a gas. Yet out of the chaos, you can still draw out nice mathematical rules like the ideal gas law PV=nRT
So is the climate well behaved like the ideal gas law, or are there complicated sources of feedback like clouds, plant growth, and albedo which make it chaotic? There are quasi-periodic alternations between the fairly cold periods of the current ice age and the interstitial we're now in, so you should recognize it's substantially more complicated than just averaging the speeds of all the molecules.
I'm all for a cleaner better world, but I'll never believe someone who says they can usefully predict a chaotic system.