Hemenway points to european famine as evidence that Ag did not produce enought to
feed. My understanding of the Irish potato famine is that it was socially derived... the Irish were exporting crops to their English overlords under the authority of the yeomans rifle straight through. This is not to say that annual Ag is not prone to instability (perhaps climate shift combined with use of marginal
land is the bigger issue), but rather that the problems of Ag are not just ecological.