The seasons won't be disrupted mate. The seasons depend on the tilt of the Earth's axis as it rotates around the sun. The worst case scenario we're looking at is a shift in the fertile zones that crops can thrive in. That shift is far easier to deal with in a global warming scenario than a global cooling scenario. If we were to be entering an ice age, crop yields would go down and food supply would shrink. As it stands, warmth and CO2 are good for plants, so it's not likely to damage food supply at all.