They can’t make the place colder but they can put a lid on industry and innovation and kill the ability of industry to adjust to a new ever colder reality.
Then, when the ice builds up on Baffin Island (which is where the big glaciers form that surge down to the Great Lakes) we can round all these guys up and prepare them as a suitible sacrifice to the "ICE GODS". Then we light some really big fires, burn a lot of coal in the least efficient manner, and demand nukes.