How Carbon Fuels Life And Warms The Planet

The following is an excerpt from Elemental: How Five Elements Changed Earth’s Past and Will Shape Our Future, by Stephen Porder.

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Elemental: How Five Elements Changed Earth's Past and Will Shape Our Future

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One of the most troubling comments from my students is that my class “Environmental Science in a Changing World” is “too depressing.” I get it. Learning about the environment is too often depressing. But oddly, I’m more optimistic now than I was ten years ago. The lessons we can learn from our world-changing predecessors, and our similarities and differences in using the elements in Life’s Formula, can pave the path towards a more sustainable future.  

My class was most depressing as I struggled to see a way forward. I am an environmental scientist—someone who uses the scientific method to observe and understand the changes humans are making to the environment around us and to understand the consequences of those changes. But I am also an environmentalist, someone who values the natural world and seeks to minimize the adverse effects of human activities. Like many environmentalists, I have spent a lot of time looking backward. What I mean by this is that I often dream of returning to an imagined, idyllic past, when humans had a light footprint and nature was left to be as it was. A lot of scholarship has shown us that this idealized past is a fantasy—at least for the last several thousand years, humans have had a big influence on the world we live in, and places that European colonists deemed empty hosted vast civilizations with profound ecological impacts.  My research and that of others in many fields have shown just how dramatic our alterations are. Despite this, the fantasy is a powerful one: a world left to its own devices, for us to enjoy, marvel in, and leave in peace.

But there are almost eight billion of us on the planet. We rely on altering the flow of the elements in life’s formula and enjoy the benefits these elements bring. What’s more, we will need more energy, more nutrients, and more water to build a more equitable future. So, I’ve slowly abandoned my dream of returning to the past. We cannot go back in time when humans were not the managers of the Earth system. At first, I had nothing to replace this idea with, and it was then that my classes were the most depressing. But the more I’ve thought about the dictates of life’s formula, the more I’ve come to think there is a way forward. Not to a future where we don’t manage the Earth system, but to a future where we manage it more wisely. Nowhere is the need for wiser management more pressing than for carbon and climate change. I’ll focus on this first and come back to the future of life’s other elements in the next chapter.

So—carbon. Yes, we’ve changed the carbon cycle. Yes, the world is warming. Yes, the chemistry of life and of our planet will make those changes inevitable as long as we continue to create elevated levels of greenhouse gases in the air. Instead of focusing on the problem, though, I want to hone in on the (potentially) life-saving difference between us and our predecessors. It is an accident of chemistry. But it is one that may allow us to avoid the inevitable world-changing fate of our predecessors.

Recall that for the cyanobacteria, whose proliferation meant the rapid rise of oxygen-generating photosynthetic organisms, there was no way to grow without pumping oxygen into the environment. The efficient photosynthetic reaction taking place in their cells had to produce oxygen. The land plants were similar constrained—their proliferation made planetary changes inevitable. The carbon stored in their bodies and their relentless attack on rocks to liberate nutrients to fuel growth eventually pulled enough CO₂ out of the air to precipitate massive changes in climate. Of course, humans play by similar physiological rules. We eat plants and animals that are full of carbon-rich compounds, break down those compounds to release energy, and breathe out CO₂. There is no way around that—it is baked into our chemistry. Fortunately for us, and in stark contrast to our world-changing predecessors, it’s not the unalterable chemical reactions inside our bodies that are causing the global carbon cycle to change. The impact of our internal chemistry on the global carbon cycle is limited because there aren’t nearly as many humans as there are of our world-changing predecessors. Plants make up more than eighty percent of all the living matter on Earth. Bacteria make up twelve percent. Humans? About one-hundredth of one percent. Our internal metabolism isn’t a big deal—there aren’t enough of us to matter.

In contrast to the other world-changers, we use vast quantities of carbon-based energy outside our bodies. This energy is released by burning fossil fuels to heat our homes, run our cars, and manufacture our goods. It is the use of this external energy that is the major driving force in climate change. That difference—between our internal and external use of energy—opens the door to a different future.

Let’s compare those two types of energy use—the internal “burning” of food calories and the external “burning” of fossil energy to power the rest of our lives. The almost eight billion humans on this planet need a lot of energy to fuel our bodies. Each of us needs about two thousand kilocalories of energy a day to stay alive. Eight, and soon to be ten, billion people, each needing two thousand calories a day, is a lot of energy required for our internal metabolism. But that number is dwarfed by the energy each of us uses to move our cars, heat our homes, keep the lights on, and make all the stuff we consume. That’s more like fifty thousand kilocalories a day per person—a ratio of twenty-five to one. For the average American, who uses way more energy on things like cars and big houses than the average person in the world, that ratio is almost one hundred to one.

This back-of-the-envelope comparison makes it clear that our global domination of the carbon cycle isn’t really about the number of people (though of course that matters). It’s about the energy those people use and the emissions of CO₂, methane, and other greenhouse gases that come with producing that energy. That is why North Americans, who account for only five percent of the human population, emit eighteen percent of all greenhouse gas. In contrast, Africans, who account for sixteen percent of the global population, are responsible for only four percent of total emissions. We all need the same number of food calories. It’s the rest of the things we do that really make the difference in terms of how much we impact the carbon cycle.

This difference from our world-changing predecessors—our need for societal, rather than biological, metabolism—is actually a saving grace. It means there is a path forward. It is a path whereby we get the energy we want to run our society in a way that does not emit greenhouse gases to the atmosphere and heat the planet at such a dizzying pace. It’s a path that was not open to our predecessors. For every additional cyanobacterium or tree, there is a heightened impact on the carbon cycle. That doesn’t have to be true for us.

Excerpted from Elemental: How Five Elements Changed Earth’s Past and Will Shape Our Future. Copyright © 2023 by Stephen Porder. Reprinted with permission from Princeton University Press. All rights reserved.