The Debate Is Over

We are entering the Oh shit era of global warming.

First there was the era of I wonder what will happen? It began more than 100 years ago when Svante Arrhenius, a great Swedish chemist, scrawled a few calculations on the back of the proverbial envelope. He estimated that humans, who were suddenly burning massive quantities of coal and oil to power the Industrial Revolution, could eventually release enough carbon dioxide to raise the temperature of the planet nine degrees. But it wasn't until the 1950s that someone got around to building an instrument to measure the CO2 in the atmosphere and found it to be, sure enough, steadily rising. And it wasn't until 1988 that a NASA scientist named James Hansen got the nerve to stand up in a congressional hearing and say that a complicated computer model he had devised of the world's climate showed that the extra carbon was heating up the planet.

Which inaugurated a second era: Can this really be true? For the next decade, governments and universities poured more money and effort into investigating this question than any that had come before. Researchers launched weather balloons and satellites; they drilled cores from glaciers and lake bottoms; they endlessly refined their computer models. By 2001, the Intergovernmental Panel on Climate Change -- which is to say all the world's climatologists -- issued a massive report summing up all the available research. Human beings, it stated flatly, were raising the temperature of the planet. So far we've made the world about one degree hotter. And according to the IPCC's forecasts, we're on track to raise it another three to ten degrees this century -- an increase that, in its middle and upper ranges, would make the planet warmer than any human, or indeed any of our primate ancestors, has ever seen it.

Those predictions were enough to get most of the world moving on climate change -- ratifying the Kyoto treaty to reduce greenhouse gases, up on the roof installing solar panels, you name it. But not us. It wasn't until this fall that Americans finally began to wake up from our denial and enter the current -- and most frightening -- era of global warming.

Katrina was the wake-up call. Hurricanes draw their power from the heat in the surface layers of the ocean, and it stood to reason that as the planet got warmer, and with it the sea, hurricanes would get stronger too. In July, MIT scientist Kerry Emanuel published a paper in Nature showing that that's just what's been happening for the past quarter century: The great storms have gotten longer (by fifty percent) and stronger (also by fifty percent). Katrina was like the Cliffs Notes version of his paper; it roared to giant life in the hot waters of the Gulf of Mexico, waters that also turned Rita into a monster a few weeks later. But the hurricanes told so many other stories too -- about governmental incompetence, about poverty and race in America -- that it was easy to lose the global-warming story in the general chaos.

Not that it mattered, because the planet was shouting the news in other ways as well. In September, scientists at the National Snow and Ice Data Center and NASA announced what their satellites were showing: The Arctic was melting in unprecedented ways. Total sea ice this summer was almost twenty percent less than normal -- a frozen area twice the size of Texas had turned to water. That's proof of global warming, but it's also a great danger in its own right. Think about it: That massive white sheet of ice is like a mirror, bouncing many of the sun's rays straight back into outer space. The blue water that replaces it is like a giant sponge, absorbing most of that solar heat and making the whole problem worse. Dr. Mark Serreze, one of the researchers, summed up their conclusion: "The feeling is, we are reaching a tipping point or threshold beyond which sea ice will not recover."

Scientists call it a positive feedback loop. And it's not the only one. Here's what a British team found in September: They'd gone back to check on nearly 6,000 little holes they'd drilled all over the U.K. since 1978. New samples from the top few inches show that as the planet has gotten warmer, the soil has become more active. Organic material is decaying and, as it does so, is giving off more carbon. A lot more carbon. Four million tons a year, to be precise -- enough heat-trapping gas to wipe out all the good work that Britain had done in the last fifteen years to stop burning coal and start building windmills. And there's no reason to suspect that the same thing isn't happening in every temperate part of the world. In the Northern Hemisphere, for instance, the growing season is about eleven days longer each year than it was in 1980 -- providing that much more time for decaying soil to leech carbon into the air. "All the consequences of global warming will occur more rapidly," says Guy Kirk, the scientist who supervised the British study. "That's the scary thing. The amount of time we have got to do something about it is smaller than we thought."

It would be easy enough to go on piling up studies like this for hours: Each issue of Science and Nature contains some terrifying new finding. Suffice it to say: It is now clear that we are changing fundamental physical systems. The progress of the seasons, the speed of the wind, the height of the oceans, a hundred other variables -- all are in flux thanks to us. Especially those of us in the United States, who with five percent of the population manage to produce twenty percent of the planet's CO2.

The worst thing about the Oh shit era is we don't know for sure exactly what will happen. Most of the changes I've been listing -- nastier storms, rising sea levels -- are pretty much linear extrapolations. If you make it hotter, they'll just keep getting worse. But researchers suspect that the world also has some trapdoors -- mechanisms that don't work in straightforward fashion, but instead trigger a nasty chain reaction. Melt enough of that Arctic ice, for instance, and you may alter the salinity of the North Atlantic enough to shut down the Gulf Stream. All of a sudden the rest of the world would be heating up, while northwestern Europe would be getting very cold. "Climate is an angry beast," Wallace Broecker, dean of the planet's climate scientists, said a few years ago. "And we are poking at it with sticks."

It's hard to imagine what it will feel like to live on an ever-warmer planet. But scientists are beginning to make progress there, too. As the computer models get better, predictions get easier. The Earth may well be:

Soggier As the planet warms, the sea level rises. Eventually this will be because ice over the Arctic and Greenland melts; for the moment it's mostly because warm water just takes up more space than cold water. No matter the cause, it's bad news, because an enormous number of people live near the coasts, especially in tropical Asia. You may be able to build levees strong enough to protect New Orleans or Miami or Rotterdam -- but Bangladesh? Computer models predict that midcentury may see 150 million "environmental refugees" forced from their homes by rising waters. That is to say, 150 Katrinas.

Sicker Who likes a warmer, wetter world? Mosquitoes do. Malaria is already appearing in places that it's never been before, including tropical cities that had been built high enough up the side of mountains to be beyond the disease's historical range. The Centers for Disease Control and Prevention predicts that another mosquito-borne killer, dengue fever, will be the emergent disease of the century, with an estimated 2.5 billion people at risk worldwide. Cases of the virus, which has no known cure or vaccine, have spiked across Asia this fall, with alarming outbreaks sweeping through Singapore, Thailand and the Philippines.

Hungrier The third-hottest summer ever across North America was in 1988, and by the time it was done, corn and soybean yields had fallen by a quarter to a third. If the temperature stays hot enough for a week or two, corn can't pollinate. Rice yields start to drop. The world already struggles to produce enough grain for a growing population -- per-capita production has actually fallen in the last twenty years. Global warming will only make the situation worse. You've heard of peak oil; keep your eyes peeled for peak food.

Poorer Skeptical that this may all be some kind of tree-hugging propaganda? The insurance industry -- the part of our economy that profits by accurately calculating risks -- has been sending up storm warnings for a decade. A recent report by three insurance experts found that payouts for everything from crop losses to wildfire damage are growing exponentially as a result of climate change. "Insured and total property losses are rising faster than premiums, population or economic growth -- both globally and in the U.S.," they warn. And that was before Katrina -- the most expensive anything ever to hit anywhere -- came ashore in the Gulf.

Science can't tell us what to do about global warming, beyond the obvious: Stop burning fossil fuels and start powering our lives with something else. By various estimates, we would need to cut worldwide fossil-fuel use by seventy percent immediately in order to keep climatic disruption to current levels. That clearly isn't going to happen. China alone adds almost fifty gigawatts of coal-fired power to its grid each year -- more than all of New England uses now. (And don't try telling the Chinese not to -- they still only use about one-eighth as much energy apiece as Americans.) Skyrocketing oil prices, meanwhile, may kill off the SUV but are also likely to increase the use of coal -- which produces even more carbon dioxide per BTU.

If the science contains any good news, it lies in the knowledge we now possess. The debate over climate change is finally over. We know that we have warmed the planet one degree so far, and we've probably already put enough carbon in the atmosphere to guarantee another couple of degrees. There is no "stopping" global warming. But we can, at last, start to take every step we can think of to slow it down. Our goal, at this late stage, is a modest but crucial one: to keep climate change from getting completely out of hand, to make it merely miserable, instead of catastrophic. If there is any hope to be had in the Oh shit era of global warming, it is that the conclusion of this story -- the greatest and most important of our time -- is still up for grabs. The ending, for better or worse, is being written now -- and we are its authors.

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