The drought that affected Australia in the first decade of this century got me interested in questions of climate change. That drought created massive bushfires in a continent that was already dry, destroying nature-spots I loved and devastating many forms of life. Intellectually, however, what gave me a jolt was the proposition—put forward in 2002 by the scientists Paul Crutzen and Eugene Stoermer—that humans had most likely brought about a new geological period in the history of the planet, one they named the Anthropocene, a time when humans acted as a major geophysical force determining the climate and the history of life on earth.

I found the idea that humans, collectively, had become capable of changing the climate of the planet for the next hundred thousand years awesome in its implications for historians who normally acquire specialist knowledge of particular groups of people at particular places, and that too covering a few hundred years at most. As a historian, I had grown up to have a deep interest in European thought, mainly political thought, and the way it had transformed lives outside Europe and been transformed in the process. I was used to the various critiques of the 1980s and later that sought to democratize the historical discipline in the Anglo-American academe: feminist critiques of patriarchy, nationalist critiques of imperialism, subaltern critiques of elitism, global critiques of Euro-centrism, semiotic critiques of ideological sign-systems, poststructuralist critiques of the subject, deconstructionist critiques of logocentrism, Marxist and liberal critiques of inequality and injustice, and, of course, critiques of history as a discipline made by those championing the cause of memory and identity. I was sympathetic to Marxist criticisms of capitalism in their broad outlines. All these critiques that shared much ground between them had made me interested in imagining the human in a particular way: as having the capacity to exercise rights, autonomy, and choice in his or her everyday life—that is to say, as an agency that could experience the world and communicate that experience. The universal human I assumed in my work, even when I emphasized the politics of difference, was the human that is the subject of phenomenology. But I saw no contradiction in this. For the phenomenological human was folded into my mental picture of the political human. The poststructuralist interrogation of the subject, I assumed with Foucault as he put it in his foreword to Deleuze and Guattari's Anti-Oedipus, was in aid of a search for nonfascist forms of life. In other words, what I had learned about the nature of power in human societies had disabused me of naïve ideas about "human freedom" and justice, but the search of justice and freedom underpinned much of the history I read and wrote. The particular intellectual endeavor I was associated with throughout the 1980s and the 1990s, Subaltern Studies, was profoundly affected by these critiques.

The scholarship of the likes of Alfred Crosby and William McNeill brought something new to the table. They made us aware of the fact that humans, themselves biological entities, lived among insects, plants, animals, birds, viruses, bacteria, and other life-forms, and their interaction needed to be made a part of the human story. I say "part of the human story" advisedly. For these historians were, understandably, not trying to do the opposite, that is, to make humans a part of the story of a virus or an insect or even to write history of humans from an animal point of view. Such a project would be impossible, for the readers of these histories were ultimately humans; so it was no wonder that the metaphors (of conquest and invasion, for example) and other figures of speech deployed by Crosby or McNeill sought to bring a sense of human drama to bear on stories of nonhuman agents—sometimes just chemical compounds such as proteins—that in themselves would be blind to the dramatic. This emphasis on the biological by the pioneers of environmental history was instructive no doubt but it did not pose any fundamental challenge to the idea of human agency as such. The biologically evolved human capacity to be healthy or diseased, to feel oppressed in slavery and joyous in liberty—as opposed to the DNA-driven "slavery" of the worker bee, for example—was assumed in radical social or "new cultural" history. Indeed, where would "contact histories" of the New World be without at least the assumption of a biological capacity that humans have to recognize each other as human even before they can share language or habitat?

The science of climate change speaks of a new kind of agency on the part of humans: a geological agency. It is collective; planetary in scope; it is not immediately available to human experience though its effects are; it is a byproduct of what we have come to regard as civilization (which needs energy to be available aplenty and cheap). There are two aspects to this proposition that interest me. First, understanding the nature of geological agency of the human and its socio-political consequences requires the historian to expand his or her imagination over a very large scale, for, as the work of the geophysicist David Archer shows, we do not understand the implications of humans' geophysical agency without learning something about both the history of earth-systems and the history of life on the planet. This is a big ask and, of course, I do not expect professional historians to be researchers in this field, but reading paleoclimatologists on the current crisis changes the "background noise" in historians' heads and affects the silent metanarratives we carry over into the microstories we tell.

Secondly, the proposition has the potential to reinvigorate debates about the nature and history of capitalism and global modernity. Some scholars argue that it is not human agency as such that has become a planetary force, climate change is simply a result of capitalist development. "It is capitalism, stupid!" is their refrain. If you pointed out to them that a Soviet-type modernization of the world would have produced very similar consequences, some of them would engage in a lot of theoretic jiu-jitsu to prove that Soviet socialism was actually capitalism in another form! (Of course, one can't argue about a "true socialism" that nobody has seen.) Some blame climate change—with justice—only on the rich countries of the world. But, going forward, what will matter in terms of emissions is not just the lifestyles of the rich but also the number of additional people who embrace existing models of economic growth and development. And most of these people are in China and India. Is the population explosion in India and China through the 1950s, '60s, and '70s to be blamed mainly on the rich countries of the West? I have had that argument put to me but the reasoning never seemed obvious. Climate change at least poses the question of one human history even if we are not politically one.

It is precisely because we are not politically one that histories of intrahuman (in)justice will remain relevant and necessary. But we will probably have to think of them in the much larger context of the history of life, how earth-history connects to it, and where humans figure in it overall.

Dipesh Chakrabarty is the Lawrence A. Kimpton Distinguished Service Professor in the Departments of History, South Asian Languages & Civilizations and the College at the University of Chicago. He is the author of several books, including Provincializing Europe: Postcolonial Thought and Historical Difference.