We have known about the origins of our disaster for longer than we like to imagine. More than 150 years ago, George Perkins Marsh (1801–1882) published Man and Nature; or, Physical Geography as Modified by Human Action — a study of how human action modifies the physical world, from the crust of the earth to the atmosphere.

The scope of Man and Nature is vast. Beginning with chapters on “the general effects and the prospective consequences of human action upon the earth’s surface and the life which peoples it”, Marsh then proceeds to trace

the history of man’s industry as exerted upon Animal and Vegetable Life, upon the Woods, upon the Waters, and upon the Sands; and to these I have added a concluding chapter upon Probable and Possible Geographical Revolutions yet to be effected by the art of man.

Despite the vastness of the project, Marsh’s message to readers was clear: If people do not take care of the earth, the earth will cease to take care of them.

If we now find this claim self-evident, this is partly due to Marsh’s “epoch-making” work. For centuries, it had been taken for granted that the resources of the land and the sea were inexhaustible. Marsh, however, mustered historical evidence against this mythological claim, pointing out that the Mediterranean landscapes described by ancient writers seldom resembled their “present physical condition”:

[M]ore than one half of their whole extent — including the provinces most celebrated for the profusion and variety of their spontaneous and their cultivated products, and for the wealth and social advancement of their inhabitants — is either deserted by civilized man and surrendered to hopeless desolation, or at least greatly reduced in both productiveness and population.

What Marsh here calls “desolation” is what’s now known as “desertification” brought about — as he also argues in Man and Nature — by the destruction of forests.

Marsh was born in rural Woodstock, Vermont, in 1801. Like his father, Charles, he would attend Dartmouth College in New Hampshire before going on to study law and serve as a representative to Congress. He wrote his many books — including an Icelandic grammar, a study of the camel, and two volumes of English linguistics — while leading an active life as a lawyer, statesman, and ambassador, first to the Ottoman Empire (in 1852–53) and later to Italy, where he would be the longest-serving envoy in US history, remaining there from 1861 until his death in 1882.

Unlike many early American conservationists, Marsh was more a scholar than an outdoorsman. Whereas John Muir made arguments for preserving the wilderness that appealed to the heart, Marsh aimed squarely at the head. He was fond of forests and other wild spaces (and played a role in the establishment of the Adirondack Park in New York State), but he emphasized above all the harm to humanity their destruction might cause — desertification, flooding, resource scarcity, and soil erosion, among other things.

Human action transforms the earth, Marsh writes in the concluding pages of Man and Nature, “though our limited faculties are at present, perhaps forever, incapable of weighing their immediate, still more their ultimate consequences.” Lest this seem like a reason to shrug our shoulders and turn our backs, Marsh adds:

But our inability to assign definite values to these causes of the disturbance of natural arrangements is not a reason for ignoring the existence of such causes […] and we are never justified in assuming a force to be insignificant because its measure is unknown, or even because no physical effect can now be traced to it as its origin.

The mystery of how our actions affect the landscape was not, Marsh wanted us to understand, an excuse for irresponsibility; it was rather a reason to take responsibility for learning about the ongoing “action and reaction between humanity and the material world”.