Can Humans Really Cause Climate Change?


I was listening to the Diane Rehm show today, on the topic of President Obama’s new proposals for reducing carbon dioxide emissions, when a man from Texas called in and stated, obviously in deep umbrage, that climate change is junk science. As proof, he pointed out that the last ice age ended with climate warming not caused by humans, so therefore climate change is natural—and only natural. He is not alone in asserting that climate change is junk science, and he is only one among many who point to the numerous instances of natural climate change, both cooling and warming, over the course of geological time.

It is true that the last ice age ended because of natural causes and was not caused by human activity. There weren’t enough humans back then to have much of an effect on climate, if any. But times have changed. Back then world population was less than one million. Today there are more than seven billion, and most of the geometric increase in population has occurred in the last 200 years (there were just barely one billion of us in 1800), and we have technologies that far exceed those that ice age man enjoyed, and almost all of our technologies are powered by fossil fuels: coal, oil, and natural gas. Because of our ability to re-shape the world in our own image, many scientists call the current era the anthropogenic age. Whereas in the past our impact on the climate was barely measurable, today it is enormous. That in the past, climate change was caused by volcanic eruptions or solar storms does not exclude other causes, including human activities. For that reason, comparisons to climate changes of the remote past are irrelevant to the situation we are facing today. Such comparisons are nothing more than red herrings, meant to distract us from the real evidence for global warming, and apparently for some people, such as that man from Texas, the fallacy is working.

Not that pre-industrial humans are completely off the hook. As documented by George Perkins Marsh in 1864 and by Jared Diamond more recently, human societies have degraded their environments through overuse since the beginnings of civilization. It is believed by archaeologists that human intrusion into the American continents by the ancestors of Native Americans led to the overhunting and extinction of many large mammals, including mammoths and several camel species. On New Zealand, Maoris slaughtered giant flightless birds, and it is believed that the original inhabitants of Australia killed off many species of large (and often dangerous) vertebrates.

Once Europeans clambered ashore in the Americas, we quickly reshaped the landscape and ecology of what became today’s United States—we felled forests, especially in the east, plowed under vast sweeps of grasslands for farmlands, dammed rivers and ruined estuaries, nearly extinguished the bison, and succeeded in wiping out the passenger pigeon, once the most numerous bird species in the world. (And note that, pointing out that extinctions in the remote past, such as the dinosaurs, were “natural” does not mean that the extinction of the passenger pigeon was not caused by humans.) The list of animal and plant species that have gone extinct because of human actions is pages long, and gets longer as more reach that sad fate every year (will the monarch butterfly be on that list soon?). Now that we are virtually in a global rather than many regional civilizations, our activities have global impacts.

The stance taken by the man from Texas, as well as those who agree with him, has behind it a disingenuous premise: That human activities are not great enough to have an effect on the global climate, and that therefore we can continue doing whatever we want without consequence. This premise is joined by another, that climate change is natural and therefore that human activity, which by (unstated) definition is not natural, has no effects. We can conquer nature because we are not-nature. But if human beings aren’t natural, what is? We are like all other vertebrate animals: We are bodies with many organs, we eat similar things to what other animals eat, we breathe, we reproduce, and we die. We are as natural, as biological, as any other organism. Therefore, we are included rather than excluded from the natural cycles of life and of the planet. We are not set apart. Even those of us who live in great cities and make our livings while seated in front of a computer screen have to eat animals and plants to survive, just like our hunter-gatherer ancestors and just like all other animals on this planet.

One of the most important atmospheric changes that ever occurred in the history of the planet was oxygenation. Nearly three billion years ago, certain bacteria, the cyanobacteria (blue-green algae), began producing oxygen, which was released into the atmosphere and made life, as we oxygen-breathing humans know it, possible. Cyanobacteria are living things (like us), and they remade the planet (like we are doing)—in a perfectly natural process. Everything that humans do is “natural”—we are incapable of doing anything unnatural. Even the burning of fossil fuels is “natural.” We didn’t invent fire, we simply found a way to use it for our own purposes. The byproducts of burning fossil fuels are also perfectly “natural”—and harmful. “Natural” does not mean benign; nor does it mean beyond human control, since “Nature” has given us the intellects and opposable thumbs to exercise control.

But there are “natural” limits to our control, limits built into our very bodies. We cannot survive and prosper without the natural environment that spawned us and sustains us. At some point the ecosystem on which we depend will snap under our pressure. Scientists warn that other species cannot evolve quickly enough to adapt to the rapid changes we have wrought. Neither can we.

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