Necessity & sufficiency, The Long Summer

I really enjoyed The Long Summer by Brian Fagan. It's a pretty interesting and multi-dimensional story, hitting all the evolutionary, archeological and climatological angles that you'd expect. Fagan's central hypothesis is that our species has been responding to local climatic shocks with short-term strategies to buffer our societies against these ups and downs, but the tradeoff has been of possible massive catastrophic effects when hit by a major oscillation. Fagan points to several civilizational collapses which might have been triggered by climatic changes (the Mayan is the most famous). But there was something that always irritated me about Fagan's narrative: he wants to really de-emphasize the role of our species in reshaping the planet and our control of our own fate. There isn't much coverage of the fact that human fires and deforestation have resculpted whole ecosystems, but what gets me is that Fagan repeatedly dismisses the impact of humans on megafaunal extinctions. The data on this seems clear: humans were not sufficient, but they were clearly necessary, in knocking out species which were already stressed because of climate change. I think this is ironic in light of the fact that Fagan tends to think in terms of oscillations and thresholds for our own species.1 - e.g., agriculture, cities, global trade and so forth.