Image: Lynda V. Mapes

Editor’s Note: The following essay, a short history of carbon and carbon dioxide, is taken from “Witness Tree: Seasons of Change with a Century-Old Oak,” which was published in its paperback form by the University of Washington Press in 2019. Mapes, who is the much-honored lead environmental reporter for The Seattle Times, wrote this book while spending a year as a Bullard Fellow in Forest Research at the Harvard Forest, in north-central Massachusetts. The book focuses on the science and story of a deeply studied old red oak tree, and its implications for understanding climate change. For more about the Witness Tree and its social media presence, here’s a link. Reprinted with permission, Copyright 2019, Lynda V. Mapes.

A simple, natural element, stored carbon has its origins in  forests. Not the Harvard Forest, or woodlands anything like them.  But in the coal forests of our planet, dating back more than three hundred million years. These forests must have been strangely  silent; there were no birds, and no mammals yet. Free of predators, scurrying supersize cockroaches more than three inches long multiplied by the millions. Big as a seagull, dragonflies whirred through the air, their two- and-a- half-foot wings churning. Giant millipedes marched over the swampy ground, with more thirty pairs of legs rippling along their nearly five-foot-long bodies.  Three- foot-long scorpions did battle, claw to claw and stinger to stinger. Towering over it all were the trees. Giant bottlebrush trees, like a modern horsetail rush, only six stories high. Or trees sprouting grassy leaves at their tops, with hundred-foot-tall, pole-like trunks, thickly armored with bark.

Long before the time of Tyrannosaurus rex and the rest of the  dinosaurs, these forests once stretched from what today is North  America to Europe, western Africa, and China. With no microbes yet on the earth that could dissolve the trees’ lignin fibers, when  all those trees died, they just fell over, sank into the swamps, and stayed there. Eventually, they formed peat deposits, layer upon  layer, and age upon age. Under great pressure and heat, over millions of years, these peat layers were compressed and transformed. They became a black, sedimentary rock, composed almost  entirely of carbon, long ago fixed by photosynthesis into those ancient trees. They became coal.

We mine and burn this coal today, all over the world. Other carbon- based fossil fuels, including oil and natural gas, were also formed from the decayed plant matter and the black ooze of diatoms and plankton sinking to the bottoms of those ancient lakes and seas, locked away in sediments millions of years ago. When we burn this fossil fuel—fossilized plants—we are bringing full circle the energy cycle that started hundreds of millions of years ago. We are taking millions of years’ worth of stored carbon, locked away underground as coal, and, by burning it, instantaneously releasing it back to the atmosphere.

This is the carbon in carbon dioxide. And it is the ever-increasing release of carbon  dioxide into the atmosphere by us, with the coming of the industrial revolution and our burning of coal and other fossil fuels, that  is the source of global climate change we are in the midst of today.

How odd that carbon, and carbon dioxide, would suddenly be  such a problem for us. Carbon is the fourth most abundant element in the universe, essential to nearly all life on the earth—as well as to many modern conveniences and luxuries. The graphite in pencils, the glittering diamond on your hand, your hand itself, the paper of this book—all are made or derived in whole or in part from carbon. The standing majesty of a tree is about 45 percent carbon, from carbon dioxide in the air, and locked by the process of photosynthesis into its leaves, wood, and roots.

Carbon dioxide is a chemical compound, produced either by burning carbon or organic matter or by respiration. A molecule of carbon dioxide is composed of one atom of carbon and two atoms of oxygen and is colorless, nonflammable, and nontoxic; it doesn’t even smell. Comprising just 0.04 percent of the atmosphere, carbon dioxide is nonetheless an outsize, powerful force, critical to setting the thermostat of the planet. Without carbon dioxide and other heat- trapping gasses, the earth would be about 33 degrees Celsius, or nearly 60 degrees Fahrenheit, cooler than it is, and mostly uninhabitable to humans. It would never be above freezing even in the temperate zones of our planet, even in summer, and agriculture as we know it would be largely impossible.

Image: Lynda V. Mapes

Preventing this moonlike state of affairs are the greenhouse gases in the earth’s atmosphere, including carbon dioxide, so-called because they function a bit like the glass in a greenhouse. As it enters our atmosphere, the radiant shortwave energy of the sun is transformed to long-wave radiation—heat. Molecules of carbon dioxide in the atmosphere absorb this heat and vibrate as they warm, creating even more heat. They also re-radiate the heat energy they absorb in random directions—including back to the earth. The effect, as these molecules block the re-radiation of heat back to space, is just the same as wrapping yourself in a  blanket or putting on a jacket to reduce heat loss. The trouble we face now isn’t that carbon dioxide is an alien force, or even in and of itself problematic. There is just too much of it. And more all  the time.

The amount of carbon dioxide in the air before the industrial revolution was largely the result of natural processes. Carbon is exuded by weathering of rocks, respiration by plants and animals, and even volcanic eruptions. It also is consumed by photosynthesis in plants, and the mixing of carbon dioxide into the seas by the waves. This natural balancing or tuning effect governs the amount of carbon in the atmosphere, land, and sea. That in turn affects everything from the pH of the seas to global average temperatures.

But when we extract oil and coal from deep within the earth and burn it in ever- increasing quantities, we disrupt this natural carbon cycle. We are releasing the stored carbon from millions of years ago back into the atmosphere as carbon dioxide over much shorter time frames than would naturally occur—and far faster than the natural carbon cycle can absorb it. Picture a big bathtub with a small drain. We keep pouring more and more into the tub, but the drain can only remove so much. That’s where we are with regard to our atmosphere. We are causing more and more carbon dioxide to build up in the atmosphere, trapping more and more of the sun’s heat. And so global average temperatures are rising.

we know the carbon dioxide in the atmosphere today is there  as a result of human activities because of the burning of fossil fuels. We know this because carbon dioxide created by burning fossil fuel bears the same chemical signature of carbon from plants: those ancient coal forests, released in a burning binge that started with the industrial revolution in 1750, with emissions increasing year by year. Burning coal has the most powerful effect on the climate because coal is the most carbon-dense fuel on the earth. Coal releases more carbon dioxide pollution into the atmosphere when it is burned than any other fuel—about twice as  much as natural gas.

In June 2013, the NOAA Earth System Research Laboratory announced the monthly average amount of carbon dioxide in the air had increased nearly 43 percent in just the last 150 years. Today, carbon dioxide levels in the atmosphere are the highest they’ve been in at least the last 800,0000 years, and maybe far longer. Because of the well-known heat-trapping properties of atmospheric carbon dioxide, human- caused climate change is not controversial among climate scientists. It follows logically that the more greenhouse gas there is in the atmosphere, the higher the earth’s average annual surface temperature will be.

The link between carbon dioxide emissions—particularly  from burning coal—and climate warming has been understood by scientists for a long time. The Irish physicist John Tyndall in the mid-1800s was the first to understand the heat-trapping capacity of carbon dioxide and other gases found in the atmosphere. Svante Arrhenius, the Swedish physicist (1859–1927), went the furthest in computing the ratios at work in the greenhouse effect. He understood the linkage between the burning of coal and the loading of carbon dioxide into the air and calculated that if we doubled carbon dioxide in the atmosphere, it would increase surface temperatures by four degrees, and if we increased it fourfold, the temperature would rise by eight degrees.

That was in 1906, and interestingly with a pencil and paper he came to roughly the same conclusion as the Intergovernmental Panel on Climate Change in its final report of 2015. But unlike the IPCC, Arrhenius saw climate change as a good thing, writing in his book Worlds in the Making, “By increasing the percentage of carbonic acid in the atmosphere we may hope to enjoy ages with more equable and better climates . . . ages when the earth will  bring forth much more abundant crops than at present for the benefit of rapidly propagating mankind.” The difference was that Arrhenius believed climate change would unfold as it had in the past, over many thousands of years. It was Alexander Graham Bell, best known for inventing the telephone, who was the first, in 1917, to coin the term greenhouse effect. Bell also understood the danger of global warming and warned against the unchecked burning of fossil fuels.

Burning coal didn’t start with the industrial revolution—that  was just a change in scale. Coal produces a lot of energy for its weight and has been central to the comfort and prosperity of people around the world for thousands of years. Cavemen heated  with coal. In America, Hopi Indians used coal to bake clay into pottery. European settlers found coal in the United States in 1673,  and the first commercial U.S. mines began operation in Virginia in the 1740s. In their fascinating article “Hydrocarbons and the Evolution of Human culture” in the journal Nature, Charles Hall  and other authors note that commercial-scale burning of hydro- carbons denotes a key evolution in human affairs:

The principal energy sources of antiquity were all derived  directly from the sun: human and animal muscle power, wood, flowing water and wind. About 300 years ago, the Industrial Revolution began with stationary wind-powered and water-powered technologies, which were essentially replaced by fossil hydrocarbons: coal in the nineteenth century, oil since the twentieth century, and now, increasingly, natural gas. The global use of hydrocarbons for fuel by  humans has increased nearly 800-fold since 1750.

In the United States, people began using coal and other fossil  fuels to replace whale oil, beeswax, kerosene, and wood at home, and waterpower, windmills, and wood and charcoal furnaces for everything from milling grain to pumping water to smelting and forging metal. Fossil fuel powered the steam engines of the industrial revolution and lit cities and homes with gaslights.  By the mid-nineteenth century, coal-powered steam engines powered the transportation revolution of railroad locomotion. By the time the big oak at Harvard Forest sprouted, more than a million Model T cars a year were coming off Henry Ford’s assembly lines, and our carbon love affair was under way in earnest, as we compressed space and time even further with flight and created a national culture of car travel. The oxen and horses of an earlier century on the land that is today’s Harvard Forest gave way to tractors, and small-scale organic farms to agribusiness, deploying an arsenal of petrochemical-derived fertilizers and pesticides. Carbon dioxide became a peculiarly human respiration, not only from our bodies, but also from our modern ways of life. Now we and our planet are suffering from too much of a good thing.

The rate of greenhouse gas emissions has not been steady  since the industrial revolution began. About half of the human-caused or anthropogenic carbon dioxide emissions between 1750 to 2011 occurred in the last 40 years, with 78 percent of those emissions contributed by fossil fuel combustion. From 2005 to 2014, the average annual rate of increase in carbon dioxide in the atmosphere was 2.11 parts per million (ppm)—more than double  the increase in the 1960s. As even those nineteenth-century scientists so well understood, increasing the amount of carbon dioxide in the atmosphere directly affects the earth’s average surface temperature.

Sure enough: the earth in 2014 saw its warmest year since record keeping began in 1880, according to two separate analyses by NASA and the National Oceanic and Atmospheric Administration (NOAA), a conclusion reinforced by others making measurements around the world. Then 2015 set a new record. The ten warmest years in the instrumental record, with the exception  of 1998, have now all occurred since 2000. The thirty-year period  from 1983 to 2012 was likely the warmest three decades of the last 800 years—and it would have been even warmer if not  for the ocean, which has absorbed most of the heat.

Meanwhile most experts think carbon dioxide levels in the atmosphere will go beyond doubling from current levels by 2100, and under worst-case scenarios probably triple. People debate whether we have entered the Anthropocene, a new geological epoch of our own making. But there’s no disputing the changes we have made to our world in just a few centuries of fossil fuel burning are of the sort usually associated with vast geologic time scales.

Image: Lynda V. Mapes

I do think it is important, as we encounter all this, to remember  that no one intended to cook the climate. We eagerly turned from wood to coal and oil to power industries and warm our homes. We invented these things to live better, more interesting, prosperous, easier, longer lives, and to expand our world and our knowledge.  All along, we were inadvertently altering the atmosphere with carbon dioxide pollution, at rates that have accelerated right along with our knowledge and ingenuity.

And now? We have, in the geologic timescale of a blink, disrupted multiple geochemical cycles and forces. From acidifying the seas, as carbon dioxide dissolves to carbonic acid, to warming the atmosphere, because of carbon dioxide’s heat-trapping properties, our world is changing.

The earth is an intricately connected system of physical  and biogeochemical cycles and interactions. The chemistry and temperature of the air, the winds, the mixing of ocean currents, the pH of the seas, the mechanics of food chains, the interactions of plants and animals and their home ranges, the fate of forests and the breathing of the trees—these are all connected. Change any part as fast as we have, and all the rest will cascade into new interactions that are already changing things for us, and many other beings with which we share the planet. Global warming, climate change, these are useless terms that fail to communicate what is really happening, notes Oliver Morton in his book Eating the Sun: How Plants Power the Planet. It isn’t just that we have  warmed the atmosphere. we have created an entirely new system, with feedbacks of its own.

What of the future? If projections in the upper end of the range of warming predicted for this century hold true, the average world temperature will increase between two and seven degrees Fahrenheit—an increase with no equal in the last 50 million years. Because it’s what we know, we think the world we’re used to is what the world will look like in the future. Actually, we’ve counted on it, building cities and villages packed with most of the world’s population and much of our most valuable infrastructure right on the ocean’s edge — heedless, even incurious, about the  ancient beach lines now hundreds of feet under water. We look at the world we see today as the only world that is or was or will ever be. But if we look into the past, it wasn’t like this, much of the  time. And surely, at the rate we are going, it’s nothing like it will be in the future.

So what now? Perhaps there will be a technological fix to this problem. Will our landscapes of the future include artificial trees—gigantic atmosphere scrubbers erected to cleanse the air day and night year-round of carbon dioxide and store it under-ground? Will we figure out how to decarbonize our energy systems and industrial processes? Break the link between prosperity and carbon? Global warming is predicted with near unanimity by scientists around the world to unleash storms, droughts, fires, pest outbreaks, floods, and species extinctions, scaling ever upward in severity according to our failure to reduce the carbon problem and stop making it worse.

Those are the broad outlines of our situation, and they are pretty simple. But it’s still an easy picture for some to ignore. Or worse, to confuse or contrive to debate as opinion what are incontrovertible physical facts. Interannual variability of the natural world and climate extremes stoked by global warming also make it easy to sow doubt.

My first year visiting at the Harvard Forest saw one of the  snowiest, coldest winters in recent years, and the second, while I  lived there, was even colder and snowier. The governor of Massachusetts called out the National Guard to shovel out the  subway system’s above ground tracks, as Boston’s transit system choked on snow. At the Harvard Forest, snow lay three feet deep on the ground on the first day of spring, with more in the forecast. The woods crew was thawing pipes as the temperature dove below zero night after night and stayed below freezing even during the day for weeks. I relished the cold and the drifted snow that simplified the landscape, burying the stone walls and reducing the palette of the forest to blue-shadowed white.

I took long walks, snowshoeing and enjoying the animal tracks. Here was an otter  slide to water, there the holes dug by gray and red squirrels digging out caches of acorns. I saw the foot prints of fishers—glorious, weasel-like carnivores—and even delicate marks in the snow from the wing sweeps of grouse, fluffing up in the cold. The paths made by porcupines traveling to hemlock groves for snacking were strewn with their fresh green nipped twigs. On just the right mornings when the sun was out and the snowflakes flat and crystalline, they flashed a brilliant prism of colors I could make sparkle and shine by turning my head to change the aspect  of the light. The winter nights were deeply dark, with sharp and burning stars.

By the spring equinox, it was clear nobody was going to even be seeing the ground in the Forest for a while. This, I thought to myself, is what scientists call the difference between weather and climate, as my car made sounds I had never heard from it before, trying to start on yet another six- degree morning.

While I froze in the Northeast, my husband at home in Seattle was cutting the grass and watching flowers burst forth in the warmest winter on record. I lived this tale of two cities, going home to sample a little spring for myself. For a few sweet sixty- degree days I was giddy with chlorophyll and early-spring bloom.  Then I came back to the Forest, shoveled out the walk to my house, and struggled to get the front door open against a thickening dam of ice drooping down from the roof. Weather at the Forest  continued to startle: record snow was followed by a near-record dry spell in April and May, then drenching rain fell, causing flooding in Boston. Aaron Ellison, a senior ecologist at the Harvard Forest, points out the sorts of extremes we are experiencing are exactly what we should be expecting: “Every day, it’s another anomaly. This is what systems do when they reach a tipping point.” Extremes of every sort are our new normal.

To be sure, changes in our planet’s atmosphere, and even our climate, have come and gone before on our adventuresome earth, over its 4.5-billion-year history. A wholesale reset is nothing new for our earth, whose climate is not terribly stable. Twenty thousand years ago, Seattle, Boston, and New York were deep under glacial ice. In just the last 12,000 years, sea levels rose nearly 400 feet, with the melting of all that ice. That’s a blink of an eye, geologically speaking. And when dinosaurs walked the earth, our planet was ice-free, all the way to the poles. Fossils tell of palms, figs, magnolias, tiny primates, and horses the size of a cat in the Arctic. Crocodiles paddled around the warm waters off Greenland. Pines grew lushly in Antarctica.

Clues to our planet’s tumultuous past are all around us, from the scratches of the receding glaciers’ claws to giant boulders lazing in fields, made of rock from distant lands, dragged and dropped there by rivers of ice. Ancient sediments perch on mountaintops, uplifted by our restless earth, packed with the fossils from the bottom of the sea. But these changes in the earth’s atmosphere, the alignments of the continents, and changeovers in whole suites of life, through five major extinctions as the planet remade itself over and over, unfolded at the pace of geologic time, over thousands and millions of years. That tempo changed with one of the planet’s newest arrivals, just 200,000 years ago. Us.

This is the crucial way in which the global climate change under way now is different from the past. First, it is caused  primarily by us, and seven billion people are trying to survive through it. And second, it is happening at a spectacularly fast rate. When global warming has happened before over the past two million years, it has taken the planet about five thousand years  to warm five degrees. The predicted rate of warming for the next century though, because of increasing concentration of carbon dioxide in the atmosphere, is at least twenty times faster.

The rate of increase is especially marked since the Great Acceleration, beginning in about 1950, with growing population, prosperity, and, notably, increased burning of coal for industry and to fire electric power plants, stoking emissions. In a new twist, escalating  carbon emissions today are tied most strongly not to population increases, but to rising energy consumption and North American–style consumerism driven by global prosperity.

What if we could see carbon dioxide gas or smell it? What if we could see great clouds of it in the air, ballooning and billowing in the sky, getting bigger by the hour, like a summer thunderhead? What if we watched this cloud blot out more of the sky, year after year after year? Would people have a better understanding of carbon and its consequences if they watched it spew from their car, airplanes, power plants, all the daily, ordinary machines, infrastructure, and activities of modern life? That this pollution is so commonplace—we all create it every day in absolutely typical activities—is what makes it so insidious, so wound into the fabric of how we do almost everything.

The disruption of our climate system could be even bigger and faster than it is, given the amount we pollute. But the natural world is helping us: the plants, the seas, the living soil, and forests absorb carbon dioxide from the atmosphere, reducing the amount of heat energy that would otherwise be trapped in the climate  system. Pastures grown back to forests have emerged as important ecological assets for capturing carbon dioxide out of the air as they consume carbon in photosynthesis. That’s why in the lexicon of climate, forests are referred to as carbon sinks: they take carbon out of the atmosphere and store it in their tissues.

Not only the stately old- growth forests and lush rain forests help. Yude Pan of the U.S. Forest Service and her collaborators discovered that the scrappy, fast-growing young forests full of intrepid trees grown up where pastures and crops once were use and store tremendous amounts  of carbon. The world’s established and re-growing forests soaked up the equivalent of 60 percent of cumulative fossil fuel emissions from 1990 to 2007, according to their 2011 paper.

That’s the lesson of the fast-growing big oak in the reestablishing woods of the Harvard Forest: the solid persistence and productivity of trees are helping to sustain our world.


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