The Weather of the Future: Heat Waves, Extreme Storms, and Other Scenes from a Climate-Changed Planet - Heidi Cullen (2010)

Epilogue. The Trillionth Ton

The large fields and acres produced no grain

The flooded fields produced no fish

The watered gardens produced no honey and wine

The heavy clouds did not rain. . . .

On its plains where grew fine plants

“lamentation reeds” now grew.

—“The Curse of Akkad,” c. 4110 BP

“The Curse of Akkad,” an epic poem known as a city lament, is believed to have been written by a Sumerian priest after the collapse of the Akkadian empire, about 4,200 years ago. The lament is considered a work of literature, although some archaeologists believe it describes actual events that detail the fall of the world’s first empire. Whatever it is, the lament is probably one reason why I became a climatologist. I wanted to know if some of those details included an abrupt change in climate.

In its heyday 4,300 years ago, the Akkadian empire, under the rule of Sargon of Akkad, stretched across Mesopotamia from the Persian Gulf to the headwaters of the Tigris and Euphrates rivers. In addition to deserving the title “world’s first emperor,” Sargon probably also deserves credit for the world’s first merger and acquisition. He successfully merged the remote agricultural hinterlands of northern Mesopotamia with the urban Babylonian city-states such as Kish, and Ur and Uruk in the south. He acquired those the old-fashioned way, with a large army.

It was a good setup, while it lasted. Northern Mesopotamia was prized for its rain-fed agriculture and served as a critical supplier of grain to the economic hubs to the south. Tell Leilan, a provincial northern capital, was part of the breadbasket Sargon had come to depend on. It served as a central processing point, distributing grain throughout his growing empire, as well as his growing army. Today, Tell Leilan, in northeastern Syria, is the site of a small Kurdish village. Tucked away in a corner of the modern Tell Leilan rests what remains of this great ancient capital. Harvey Weiss, a professor at Yale University, returns here every few years to excavate. I had been working with Weiss on the collapse of Akkadia for more than four years before I ever saw what remains of this ancient Akkadian capital.

You could say that my experiences, until I joined Weiss and his team of archaeologists on a dig in the summer of 1999, had been only vicarious. I had studied ancient Near Eastern history, modern Middle East policy, Arabic, and of course, climate. I was what you might call book smart. I could tell you the average high temperature and wind speed for northeastern Syria in July, but that didn’t mean much until I stood on a dig site for eight hours a day in 110°F heat taking in mouthfuls of windblown dust. I may have been there in my head, but the real experience was a whole different ball game. As with most things in life, including global warming, there is something important to be said for personal experience.

Weiss’s previous excavations had shown that between 4,600 and 4,400 years ago, Tell Leilan grew about sixfold in size, from 37 acres to more than 200 acres.1 The city’s residential quarters showed signs of urban planning, including straight streets lined with potsherds and with drainage lanes; and its acropolis contained several storerooms for grain distribution. But sometime around 4,200 years ago, this society began to fall apart and archaeological evidence indicates a mass exodus from Tell Leilan to points south. Tell Leilan was abandoned and sat empty for some 300 years. It was probably during this abandonment period that the city lament was composed. After less than 100 years, the world’s first empire was gone.

At least, this was the story when I signed on to research the Akkadian collapse. Weiss had assembled enough archaeological evidence to suggest, at least to him, that the Akkadian empire had collapsed abruptly because of a rapidly changing climate. However, he had no data on climate to support this theory. And without such data, the story of Tell Leilan was just that, a sad story told in the form of an epic poem. With the help and guidance of Peter deMenocal, one of my PhD advisers at Columbia University, I obtained the top 6 feet of a long ocean sediment core that had been pulled up from the bottom of the Gulf of Oman. We intended to use the core to reconstruct the climate of Mesopotamia over the geologic period known as the Holocene, which spans the last 10,000 years. By taking samples at half-inch intervals down the entire length of the core, I was able to build a history of Mesopotamian climate in 100-year steps, using only dried mud from the bottom of the sea. The ocean floor remembers everything.

Mesopotamia is a notoriously dusty place, and the dust there is predominantly composed of a mineral, dolomite. Mesopotamia is also a notoriously windy place. When its steady southwest wind, called the shamal, kicks up, that dust is transported and dumped into the Persian Gulf and the Gulf of Oman. Technically, my mud from the Gulf of Oman was actually Mesopotamian dust. Everything has to come from somewhere.

I spent my first semester of grad school in the lab at Lamont-Doherty Earth Observatory, crushing dried core samples and measuring the concentration of dolomite in each sample. The goal was to reconstruct a history of Mesopotamian drought. On the basis of soil characteristics and prevailing winds, the more dolomite in my mud sample, the more drought in Mesopotamia, and the more trouble for Sargon.

Grinding, measuring, and running about 200 samples consumed the better part of my life for more than a year. When the work was finally complete, I had an elegant spike about one-third of the way down the core to show for my effort.2 According to the X-ray diffractometer (XRD) analysis, this spike meant the amount of dolomite in that one particular sample was six times higher than it had been throughout the rest of the Holocene. That spike suggested that a severe drought had gripped Mesopotamia for more than a century. And according to the AMS dates, the spike in dolomite occurred very close to 4,200 years ago, at about the time a weary Sumerian priest was sitting down to write an epic poem of collapse. Weiss had taken the city lament at its word, and our ocean sediment core suggests he was right. The world’s first empire stood for just 100 years. In the end, it amounted to less than 1 inch of mud at the bottom of the ocean.

The United Nations Framework Convention on Climate Change (UNFCCC), an international environmental treaty crafted at the Earth Summit, held in Rio de Janeiro in 1992, was ratified by 192 countries, including the United States.3 The stated objective of the Convention (Article 2) is to stabilize atmospheric concentrations of greenhouse gas at a low enough level to “prevent dangerous human interference with the climate system.” The words dangerous human interference, carefully selected by diplomats and policy makers, are not the language of scientists.

“One of the things that has always been difficult about the concept of dangerous human interference is that it involves value judgments,” explains Susan Solomon, a senior scientist with NOAA. But in 1996, using the best available science, the members of the European Union decided to make a value judgment. They agreed that a temperature increase of 3.6°F above the preindustrial global average temperature constituted dangerous human interference with the climate system. And in order to avoid severe, widespread impacts they argued that there was a need to keep global warming below that level.

Solomon knows that workings of the policy world quite well. She cochaired Working Group 1 for the IPCC Fourth Assessment Report, and research done earlier in her career on the ozone hole provided the scientific foundation for the UN Montreal Protocol, the international agreement to protect the ozone layer. Solomon had helped prove the existence and cause of the ozone hole after leading an expedition to McMurdo Sound, Antarctica, in 1986. The ozone hole appears in the early spring, so Solomon and her team spent months in Antarctica, enduring brutally cold temperatures and nearly twenty-four-hour darkness, in order to observe the hole as it formed. She and her team were able to gather enough data to provide the first evidence that enhanced levels of chlorine oxide from the chlorofluorocarbons (CFCs) were the primary cause of the ozone hole.4 The CFCs, stable compounds used in refrigerators, in air conditioners, and as a propellant in aerosol cans, were reacting with the clouds in the stratosphere to destroy the protective ozone layer. Solomon and her colleagues had the data to prove it.

Global warming is somewhat less straightforward. “How do you decide what a dangerous level of human interference means?” Solomon asks. “It’s been a real challenge as far as what science can do to inform that process without becoming, frankly, unscientific,” she explains. “It’s not as clear-cut as observing an Antarctic ozone hole form.” That’s why Solomon chose to focus on another principle of the UNFCCC. Article 3 of the Convention emphasizes “threats of serious or irreversible damage.”

“And I can tell you from the amount of time I spent around the diplomatic folks during the IPCC process that when they say ‘serious or irreversible damage,’ that’s what they mean. If they meant to say serious and irreversible, they would have said so. They probably spent five days negotiating whether it was going to be serious ‘or’ or serious ‘and,’ ” she adds. Solomon was struck by the word irreversible. “Irreversible is something that doesn’t involve any value judgments. Something is either irreversible or it’s not,” she says. “That is a piece of the problem that science can inform.” And in a recent research paper, Solomon looked at the extent to which human influence on the climate is irreversible. What she discovered surprised even her.

Until recently, most scientists were working under the assumption that if we went cold turkey and brought CO2 emissions to zero, CO2 concentrations measured in parts per million (ppm) in the atmosphere would peak and then fall most of the way down toward preindustrial levels in about 100 to 200 years, with the warming decreasing along with them. Solomon and her colleagues, using a climate model known as an Earth-system model of intermediate complexity (EMIC), wanted to see for themselves how long it would take for the concentration and climate to head down. An EMIC is not as fancy as a general circulation model, but it has the advantage of being fast. So Solomon was able to run very long simulations of the Earth’s climate and see what the atmosphere remembered of us 1,000 years from now, in the year 3000. The experiment tested what would happen if CO2 emissions suddenly stopped after peaking at different concentrations, ranging from 450 to 1,200 ppm.5 In their model, CO2 levels dropped so slowly that by the year 3000 the atmospheric concentration was still substantially above preindustrial levels. Global temperatures also stayed high. The atmosphere turns out to have a better memory than we thought.

“Somebody said to me recently that I’ve introduced two words into this debate that just weren’t there before. And they are unequivocal and irreversible,” Solomon says. “And that’s not a bad set of words.” It was Solomon, armed with her thesaurus, who introduced the now famous word unequivocal into the IPCC Working Group I Summary for Policymakers.6 For scientists, the statement reads like Hemingway, concise and powerful:

Warming of the climate system is unequivocal, as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice and rising global average sea level.

The statement reflects the kind of pure, scientific analysis and multiple lines of evidence that Solomon is passionate about. She is someone who draws a sharp line in the sand between science and politics.7 Her personal opinions, she has said repeatedly, have no place in the policy arena.

“When we came up with unequivocal, some people said it wouldn’t stick. It’s too complicated. We thought a lot about what word to use. And we played around with words like incontrovertible and undeniable. But we didn’t want to use those, because they were too political in their tone. They are not the kind of words you would see in a scientific paper,” Solomon explains. “We went with it because it’s not a statement about how others are reacting to the science, it’s a very internal statement about the nature of the evidence,” she says. This was a word that represented science, not politics.

“The fact that you have independent measurements not just of temperature, but also of sea level rise, and retreat of Arctic sea ice, and retreat of glaciers worldwide, increases in water vapor, all of which fit what we know should be happening on a warming planet,” Solomon says—“that is the reason we were able to use this word.” The science, in other words, speaks for itself.

Solomon’s second word is no less powerful. “Article 3 of the framework convention is a recognition that things that are irreversible deserve special attention. Because it means you can’t back out of them,” she explains. But aside from death and taxes, irreversibility is not a concept we Americans tend to embrace. “The thing that makes this tricky is that just about any other pollution problem—acid rain, smog, DDT—works in a straightforward way. When you stop emitting, the problem goes away. The thing that’s really hard here is that we’ve recognized it’s not going to work that way with global warming. We’re turning the dial on the global temperature as if it were a thermostat. But it only cranks one way. We don’t get to turn it back down,” she says. History has not been kind to those who have failed to understand the physics of the irreversible. Just look at a symbol of irreversibility, Easter Island.

Settled by Polynesians sometime around a.d. 900, Easter Island is an isolated 66-square-mile chunk of volcanic land situated in the middle of the Pacific Ocean between Peru and Australia. The volcanic tuff was carved to create the enormous stone statues, called maoi, that made Easter Island famous. The Polynesians used tree trunks to transport and erect the maoi. In fact, trees made much of life on the remote island possible. And archaeological evidence suggests that at one time Easter Island had a diverse forest. The bark of certain trees was used to make rope or beaten into cloth; other trees were used to build canoes, or to make harpoons.

The canoes and harpoons were essential, as the common dolphin, a porpoise weighing up to 165 pounds, was the main source of meat on the island. The Polynesians hunted with harpoons from large wooden canoes, far from the shore. Palms were probably the most important trees. The trunks provided sap that could be fermented to make wine, honey, and sugar. The fronds were ideal for thatching houses, and for making baskets, mats, and boat sails. It would seem as if the only things not made of wood on Easter Island were the maoi, which are thought to represent high-ranking ancestors. Wood was used for so many aspects of life on the island that by 1722, when the Dutch explorer Jacob Rogeveen arrived on the island, he saw no trees more than 10 feet tall. The gradual deforestation was nearly complete. Today, Easter Island serves as one of the most extreme examples of forest destruction in all of history.

Deforestation made it impossible for the Polynesians to build the canoes that allowed them to catch porpoises. Land birds, with no trees to nest in, disappeared. Palm nuts, Malay apples, and all other wild fruits were gone. The deforestation also led to soil erosion that resulted in reduced agricultural yields. It is believed that deforestation set off a chain of events that eventually led to collapse. The population dropped sharply and the construction of the maoi ceased. The only things left to eat on the island were rats and people. In his book Collapse, Jared Diamond says:

I have often asked myself, “What did the Easter Islander who cut down the last palm tree say while he was doing it?” Like modern loggers, did he shout “Jobs, not trees!”? Or: “Technology will solve our problems, never fear, we’ll find a substitute for wood”? Or: “We don’t have proof that there aren’t palms somewhere else on Easter, we need more research, your proposed ban on logging is premature and driven by fear mongering”? Similar questions arise for every society that has inadvertently damaged its environment, including ours.8

This begs the question: with regard to global warming, what is the equivalent of cutting down the last palm tree? The answer may not be simple, but if you accept the meaning of the words unequivocal and irreversible, and you accept the implied value judgment of 3.6°F warming, you can come up with a fairly good proxy. “If you accept that, you can now calculate how many gigatons of carbon you can emit and keep warming below 3.6°F,” Solomon says. Scientists can boil it down to one number. And that number is 1 trillion.

Myles Allen—a professor at the University of Oxford—and his colleagues found that if we could limit all CO2 emissions from fossil fuels and changes in land use to 1 trillion tons of carbon in total, there would be a good chance that the climate would not warm more than 3.6°F above its preindustrial range.9 A companion study, by Malte Meinshausen at the Potsdam Institute, found that the world would have to limit emissions of all greenhouse gases, not just CO2, to the equivalent of 400 gigatons of carbon between 2000 and 2050 in order to stand a 75 percent chance of avoiding more than 3.6°F of warming.10 The other greenhouse gases, such as methane and nitrous oxide, are expected to produce as much warming as 125 gigatons of carbon in the form of CO2; that means emissions of CO2 itself over the next forty years have to add up to less than 275 gigatons of carbon. No one said this was going to be easy.

That is especially true when you consider how much CO2 we’ve put up there already. Since the start of the industrial revolution about 250 years ago, we’ve burned about half of the 1 trillion tons. Global emissions currently average about 9 billion tons a year, and they’re rising. In May 2009, the Energy Information Administration (EIA) released International Energy Outlook 2009, an annual report that projects energy trends through 2030. The report concluded that with no further policies to reduce CO2 emissions, total global emissions will reach about 11 billion tons of carbon by 2030. The jump in emissions is attributed to a projected 44 percent increase in energy demand by 2030, much of it produced from fossil fuels. Renewable energy is expected to grow fastest, but fossil fuels will continue to serve as the dominant source of energy to meet the growing demand coming from developing nations. The report says 94 percent of the increase in industrial energy use between now and 2030 is expected to take place in developing countries; Brazil, Russia, India, and China are expected to account for two-thirds of that growth.11

The implications are simple: the more CO2 we dump into the atmosphere, the warmer it gets, and the more serious and irreversible the damage. If carbon emissions were trees, then the more we’ve cut down by 2020, the fewer will be left to cut by 2050. In essence, the 1 trillion-ton limit allows the world to follow its current trend for about forty more years before having to quit carbon cold turkey, all at once. Somewhere out there, in a coal seam in Wyoming or an oil field in Saudi Arabia, sits the trillionth ton. Unless scientists come up with some way to suck CO2 out of the atmosphere or a cheap form of renewable energy, the fate of that trillionth ton rests in the hands of policy makers, not scientists.

In December 2009, seventeen years after the Earth Summit in Rio de Janeiro, policy makers and scientists gathered once again at the Conference of the Parties (COP 15) in Copenhagen, Denmark. Since the ratification of the UNFCCC, they have been using these conferences to assess progress and establish legally binding obligations for countries to reduce their greenhouse gas emissions. It was at COP 3 in 1997 that the Kyoto Protocol first set binding targets for reducing greenhouse gas emissions. The overall goal for COP 15 was to establish a new global climate agreement to replace the Kyoto Protocol when it expires in 2012. Dozens of countries, including China and the United States—the top two carbon polluters—came to Copenhagen with proposals to cut their emissions. But in the end, world leaders left the meeting with a deal that was seen as weak and lacking in detail. Although it did set up the first major program of aid to help poorer nations adapt to climate change, it offered few specifics in terms of pollution reductions. Upon the announcement of the deal, a team of experts led by a professor at MIT made a quick calculation that converted the language of policy makers into the language of scientists. As it stood, the deal was likely to result in a 5.7°F rise in average global temperature. In the end, the words of science—unequivocal and irreversible—were still not powerful enough to shift the forecast for the future.