For most of John Brooke's new book the phrase “climate change” is shorn of the familiar qualifier “anthropogenic” and so of its current political connotations. Climates here are changing persistently and regardless of human activity, for centuries and millennia from drought to deep freeze. Brooke tracks these changes beginning in prehistoric epochs and ending in the twenty-first century, narrating the history of Earth's climate alongside the history of its human inhabitants in order to sketch the causal relationship between the two. This is history both broad and deep, ranging over much of the planet and several million years.

Climate, Brooke argues, has played a much more direct role in human history than most scholars would allow. Despite historians' general reluctance to accept that “natural forces in some way circumscribe human agency,” for millennia climatic conditions have set both hard limits to human activity and triggered concentrated bursts of innovation and adaptation (p. 2). People act, decisively, in Brooke's account: they invent tools and symbolic language, engage in political and religious practices, and exploit natural resources as well as other peoples and polities. But behind all that human busyness the planet's orbit and axis shift, tectonic and volcanic activity increases and settles, sunspots emerge and fade, and the Intertropical Convergence Zone wanders north and south of the equator. These various climatic phenomena set the terms for whatever human communities try to do, providing “the framing conditions in which human societies mobilized to change their circumstances” (p. 165, italics in original).

Natural forces do not just matter in Brooke's telling of history; they are central. At times they are determinative. The agricultural revolution of roughly ten thousand years ago, for instance, was a moment of ultimate contingency. “Without the warming of the earth with the end of the Pleistocene,” Brooke writes, “the transition to food production and the entire subsequent course of human civilization could never have unfolded” (p. 129). When people started tending to crops things began to heat up, in several senses. Human reliance on agriculture meant even greater human reliance on a stable and agreeable climate, making changes in that climate ever more consequential.

While Brooke insists on the centrality of the natural world to human existence, though, he is no doctrinaire environmentalist. His chief intellectual adversary may be Thomas Malthus and the Malthusian tradition of explaining societal collapse in terms of populations outrunning their resource bases. This, according to Brooke, is the “endogenous argument”: locating the source of crisis in human behavior. Brooke subscribes, instead, to the “exogenous argument,” emphasizing the role of outside forces like drought, cold, and epidemic disease in most if not all civilizational declines before the modern era. Brooke rejects Malthusian gradualism, in which variables like population, resources, and technological innovation increase at predictable rates until they push the limits of sustainability. Instead he embraces economic and ecological models that feature dramatic and seemingly sudden change. For economists like Joseph Schumpeter this meant technological intensifications and breakthroughs that mitigated crisis, and for natural scientists like Stephen Jay Gould and Niles Eldredge it was the acceleration of natural selection in the wake of catastrophic environmental change. In both cases, abrupt shifts triggered adaptation. Early human societies, then, were generally stable and successful affairs intermittently disrupted by climatic transitions, rather than shaky enterprises always sliding toward disaster. If Malthus thought of human history as a ragged march along a cliff's edge, Brooke thinks of it more as a steady procession across an open field with the threat of storms always on the horizon.

Climate Change and the Course of Global History is a remarkable synthesis of ecological, biological, anthropological, historical, and climatological scholarship. The range of Brooke's sources reflects the scope of his narrative. He draws widely without sacrificing complexity; a significant number of the book's nearly 600 pages describe various debates among researchers about matters major and minor. Scholarship has its own dramatic shifts in intellectual climate, and Brooke somehow manages to keep track of local weather patterns for a stunning array of disciplines. As Brooke's evidence piles up it becomes difficult not to understand upheaval after upheaval—from the decline of Mesopotamians, Romans, and pre-Columbian Native Americans to the rise of agriculture, animal husbandry, and iron tools—as consequences of climatic shifts. Sweeping explanations are always suspicious and Brooke admits that he “may be condemned for crude determinism,” but whether or not the book overstates its case it is a fascinating approach to understanding pivotal changes in human history (p. 287).

This is a work of history rather than politics, descriptive rather than prescriptive, and Brooke's interest is in the past. Still, by the book's coda, “climate change” has taken on its more familiar, contemporary urgency, and Brooke ends by advising readers, “We hold it in our collective capacity to address the earth system crisis that is now upon us. That capacity must be mobilized by an informed political will” (p. 579). That message does not immediately follow the thrust of the book that preceded it, though. It is difficult to feel the same sense of urgency after hundreds of pages of climate-induced crises that, while devastating, produced more sophisticated and resilient human societies. One possible lesson of Brooke's study is that “climate change” in whatever sense has always been a natural part of human history and, in the long run, a fortifying one.

Brooke clearly does not subscribe to this view, and argues that climate change this time around is different. He spends much of the book's final chapters explaining the qualitative changes from the pre-industrial to the modern, industrialized world. The early modern period is “the fundamental hinge of human history,” during which humanity begins to escape the deterministic forces of climate and disease (p. 413). The calculus that has explained several millennia starts to lose its purchase, and “suddenly Malthus does begin to really matter” (p. 468). In fact, the modern era witnesses “the transition from essentially exogenously driven to endogenously driven crises” (p. 473, italics in original). China suffers a genuine Malthusian crisis and England avoids one only through the resources of its empire and the abundance of its coal. Things accelerate in the twentieth century as populations blossom and energy use skyrockets. The old story of people reacting to the force of climatological shifts reverses itself, and humans unwittingly begin to control the climate. The cost of relatively stable, predictable, and sustained individual lives in the modern era is unstable, unpredictable, and unsustainable societies. Modern people become the authors of their own impending catastrophe.

Does it matter, though, that climate change this time around is anthropogenic? Already a new school of optimistic environmentalists has counseled greater acceptance of climate change, noting that the planet has weathered much worse and that with sufficient preparation we can mitigate the harms. Whether exogenous or endogenous, climate change is a condition of living on this planet and one that people have endured in the past and will endure in the future. “It's natural” has long been a way of undermining concerns about climate change, mass extinction, and various forms of pollution, and Brooke's emphasis on the persistent role of climate change in human history offers the possibility that this latest episode is simply business as usual. Brooke's study may unintentionally lend support to a sort of normalization of crisis.

Whether or not Climate Change and the Course of Global History enters into contemporary discussions about planetwide temperatures, it will certainly become a key text for understanding global and deep history and for bringing together scientific and social scientific scholarship. Brooke's voluminous research has broken a path up a very steep hill, and the view from the top is a much wider one.