Actually, higher levels of CO2 in the atmosphere make agriculture more efficient: plants grow faster, produce more, and are more resistant to drought. Warmer temperatures in Northern regions — where the greatest warming, if it occurs at all, is predicted will be extremely beneficial by extending growing seasons and allowing agriculture zones to spread into areas previously too cold to farm. On a cost benefit basis, a few degrees of warming — again, if it occurs at all, which is highly uncertain — will be a great benefit to mankind overall, as previous warm periods have been. There is no basis to conclude that the climate of 1950 was the “perfect” climate which should be maintained without change for all time. A cooling world would be a much greater calamity for mankind, again as it has been in the past.
PS: And there is no actual evidence to date that the much predicted increase in number and severity of extreme weather due to a warmer world is in fact occurring. The US has not been hit by a major hurricane for years and increases in tornadic activity are attributable entirely to better data capture not an actual increase in the activity.