@Green Witch,
Quote:We have grown food for thousands of years based on fairly steady frost dates and temperature ranges within geographical zones. If we lose this predictability we may lose our stable food supply.
This is not entirely true. It is largely true for Eurasia, but not for Africa and the Americas. Plants which were domesticated elsewhere and diffused into Africa could not spread through tropical areas to temperate zones south of the equator, and plants domesticated on the North African coast and in the Sahel could similarly not be diffused across the tropical zones.
The middle east and China both appear to have been the earliest centers of the domestication of plants and animals. Those domesticates were available for diffusion to the east and west because they all essentially arose in the northern temperate zone, and could therefore thrive almost anywhere else in the northern temperate zone. The most important factors were the length of the day, and when the rains come. Climate change is not going to affect the length of the day. It is possible, but it is not inevitable, that the rainfall patterns could change. Plants which were attuned to winter rainfall (such as the two types of wheat, barley and the pulse crops of the middle east) cannot be spread to areas which have summer rainfall. So, for example, the plants domesticated by the Bantu south of the equator in Africa were domesticated in a summer rainfall area. They did not migrate beyond the Fish River, because although southern Africa has a typical mediterranean temperate zone climate such as is found in the middle east and the Sahel, that means winter rainfall, and the plants domesticated by the Bantu south of the equator were attuned to a summer rainfall.
Frosts don't actually have much to do with the spread of domesticated plant foods, except that it was necessary to develop strains of those plants which came to fruition in a shorter growing season. The major "suite" of middle eastern crops were all plants which could be so adapted, and harvest precedes the frost. That was actually not all that difficult because the length of daylight in "higher" (i.e., more northern in the northern hemisphere) temperate zone regions increases more rapidly in those areas, and the length of daylight at the solstice is much greater--so the domesticated plants adjusted fairly quickly (a few thousand years in the absence of intelligent agronomic manipulation). With the agronomic technology we have today, the ability to quickly respond to changing climactic conditions means that solutions can be found in a lot less time than the thousands of years it seems to have taken to adapt middle eastern or central China domesticates to more northern or more southern areas of the temperate zone.
The problems climate change will create for crops is that areas which are now optimal because of rainfall patterns may become too arid for the crops now being grown there. But at the same time, areas which are now too arid may become candidates for intensive agriculture. At the time of Caesar Augustus, North Africa and Egypt were the breadbasket of the empire. It might be difficult for the rather low tech farmers of North Africa and Egypt to adjust if their climate becomes wetter, but i'm sure the prospect of profits will reconcile them to the difficulties. The bigger problem will the the economic dislocation of food producers in the current intensive agriculture areas of the world, if rainfall patterns alter sufficiently to endanger their livelihoods.
