We need more books like Brian Fagan's 2008 The Great Warming: Climate Change and the Rise and Fall of Civilizations: history books, mostly, that help us understand that climate change isn't just about changes in some abstract "the environment," but about great changes in human politics.
This book is about "the Medieval Warm Period," ca. 800-1300 C.E. and its generally positive effects in, e.g., northern Europe and utterly devastating effects elsewhere, e.g., in already warm, dry places such as long-term droughts in what's now the U.S. southwest.
These Medieval data can cut different ways, as a warning to try to reduce the speed of global warming and try to mitigate its effects — or to say that climate change ca. 900 obviously wasn't caused by human industrial activity, so we needn't reduce current economic activity with its benefits and irrelevant, or even beneficial greenhouse gas emissions.
To quote for background one on-line pundit, "Climate scientists now understand that the Medieval Warm Period was caused by an increase in solar radiation and a decrease in volcanic activity, which both promote warming. Other evidence suggests ocean circulation patterns shifted to bring warmer seawater into the North Atlantic." So why should we try to reduce greenhouse gasses?
The question isn't rhetorical. For one thing, the article linked last paragraph notes that there's no evidence for a recent increase of solar radiation, nor, in our times, significant decrease of volcanic activity;, and I'll note that currently there's not a damn thing the human species can do about either. We can reduce emissions of greenhouse gasses, which will slow the rate of warming, and we should reduce those emissions anyway to save some easily extractable hydrocarbons for our descendants. They might find safe and efficient ways to use petrochemicals and need some — and be very pissed off at earlier generations who went and burned them.
They may also be pissed off at a re-run, but worse, of, especially, long-term, catastrophic droughts.
In addition to the obvious, some of the effects of climate changes indeed include the geo-political. William Grimes's New York Times review of The Great Warming has an arresting sentence indicating that what was so good for much of Europe may have had negative effects: "Although data remain sketchy, it seems probable that extended droughts dried up pastureland on the Central Asian steppe, propelling the armies of Genghis Khan westward." The career of the Great Khan (1206-1227 C.E.) achieved some impressive empire building that, in Europe, arguably set the stage for what was once called the Renaissance, but unarguably resulted in an extraordinarily high body-count. Matthew White tallies up Genghis Khan's "multicide" score at 40 million, which puts the Mongol invasions just behind World War II (1939-1945) for destruction of human life.
And destruction of the great Muslim civilizations at the center of Eurasia — which in a twisted way brings me to where I started thinking about this post.
I had typed out on Facebook a quotation from Introduction to Medieval Europe: 300-1500 by James Westfall Thompson and Edgar Nathaniel Johnson (New York: Norton: 1937). In an early chapter on "The Empire of the Arabs," Thompson and Johnson give Mohammed and the early leaders of the Umma credit for organizational genius and make the point that medieval Europe was a side-show as civilizations of the time went. They are far from "climatic determinists," with an Index innocent of such references. And they fully recognized the arrogance and stupidity of the remaining Roman Empire and Persia in their continuing wars and machinations. Still, Thompson and Johnson asserted (in 1937!) that "The expansion of the Arabs is best understood in the light of previous movements out of the desert [...]. These were constant phenomena, to be explained by the vicissitudes of climatic conditions, which always drove nomadic peoples outwards. [...] The [Arabian] peninsula itself was experiencing a periodic desiccation, which made life within it ever more unbearable and drove its inhabitants to seek relief elsewhere. It seems, accordingly, highly probably that what occurred would have happened even without Mohammed and Islam" (p. 166).
"What occurred" was the end of Late Antiquity, with the final end of the Roman Empire, and the Persian — and Rome in the East (the Byzantine Empire), reduced to a regional power. T & J and those with similar theories may be wrong, but it's a point to consider, along with the possibility that the following round of "desiccation" in the Medieval Warm Period led to that drying out of parts of the Eurasian steppe leading to the western thrust of the Mongol invasions and, let's say, a figurative arrow from a powerful bow through the figurative heart of "The Empire of the Arabs."
It's possible that two major changes in the course of human history had as one basic cause the long-term droughts — the "desiccation" — brought on by global warming. Mohammed and Genghis Khan count, and their decisions are important. Still, one thing Karl Marx got right was that "Men make their own history, but they do not make it as they please [...], but under circumstances existing already, given and transmitted from the past." And those circumstances include a physical environment that is both beyond human control and influenced by our actions.
Unless we want some really bad circumstances for the next generation, we'd better get right some important decisions — and soon.