Wouldn't the cow issue be related to our interference. Im fairly sure we made them bigger and beefier, combined with the fact we have made more than there were to being with....

Im pretty sure trees do actually take in some C02 (mostly in but occasionally they release some) and whilst planting trees may not be the most effective thing I don't think this too much harm planting a few, we have cut down counltess numbers over the years so I wouldn't say its a bad thing. Trees are quite nice also....