With Speed and Violence: Why Scientists Fear Tipping Points in Climate Change (31 page)

The Atlantic is also generating hurricanes in places where they have never been seen before. In March 2004, the first known hurricane in the South Atlantic formed, striking southern Brazil. That the hurricane, later named Catarina, even formed was startling enough. What caused the greatest shock was that it developed very close to a zone of ocean pinpointed a few years before by Britain's Hadley Centre modelers as a likely new focus for hurricane formation in a warmer greenhouse world. But they had predicted that the waters there wouldn't be up to the task till 2070. Many saw Catarina as a further sign that global warming was making its presence felt in the hurricane world rather ahead of schedule.

The billion-dollar question (literally so for insurance companies) is whether there is now a discernible climate change component at work in the frequency and intensity of hurricanes. Kerry Emanuel, for one, argues that whatever the natural variability, the "large upswing" in hurricanes in the North Atlantic in the past decade is "unprecedented, and probably reflects the effect of global warming." Jim Hansen weighed in at the end of 2005, insisting that climate change was the cause of a warmer tropical Atlantic and that "the contention that hurricane formation has nothing to do with global warming seems irrational and untenable."

The matter of North Atlantic hurricane trends is likely to be debated for many years yet. The "signal" of climate change will be difficult to disentangle from the "noise" of natural variability. But while it is easy to become obsessed with hurricanes in the North Atlantic, they amount to only around a tenth of the global total-and a rather smaller proportion of those that make landfall in a typical year. The biggest source of hurricanes is, and is likely to remain, in the western Pacific, where they terrorize vulnerable and densely populated nations like the Philippines, Vietnam, and China. So it is the global picture that both matters most and is most likely to resolve the issue of the impact of climate change.

Several research groups have been scouring records of past hurricanes worldwide to see if there is any evidence of a trend as the world has warmed. Emanuel has concluded that, on average, storms are lasting 6o percent longer and generating wind speeds 15 percent higher than they did back in the 195os. The damage done by a hurricane is proportional not to the wind speed but to the wind speed cubed. And Emanuel's results suggest that the destructive power of a typical hurricane has increased by an alarming 70 percent. "Global tropical cyclone activity is responding in a rather large way to global warming," he says.

Others are coming to agree. Only weeks after Emanuel's paper appeared, in the autumn of 2005, three other leading hurricane researchers published a similarly alarming conclusion. Peter Webster and Judy Curry, of the Georgia Institute of Technology, and Greg Holland, of NCAR, concluded that while there had been no overall increase in the number of hurricanes worldwide, the frequency of the strongest storms-categories 4 and 5-had almost doubled since the early r97os. They now made up 35 percent of the total, compared with 20 percent just three decades before. The trend, the researchers said, was global, and they agreed with Emanuel that it was clearly connected to the worldwide rise in sea surface temperatures. That made it extremely unlikely that natural cycles, which are relatively short-term and confined to single ocean basins, were causing the trend. "We can say with confidence that the trends in sea surface temperatures and hurricane intensity are connected to climate change," Curry declared.

William Gray and some other traditional hurricane forecasters have contested the findings, claiming that some of the data, particularly old estimates of wind speed from the Pacific in the 197os, are flawed. In an increasingly vitriolic exchange, Gray argued that the papers simply could not be true. Emanuel and Webster agree that the data are not as good as they might like. But "Gray has not brought to my attention any difficulties with the data [of] which I was not already aware," Emanuel said, with some irritation. Webster says Gray is "grasping at thin air."

So where does that leave us? There is as yet nothing unique about recent individual hurricanes, though Katrina, Wilma, and Mitch clearly stretch the bounds of what can be regarded as normal. The largest and most powerful hurricane ever recorded, Typhoon Tip, with wind speeds of more than i 8o miles per hour, grazed Japan a quarter of a century ago, in 1979. The storm that hit Galveston in i9oo killed ro,ooo people, many more than Katrina. Both pale compared with a hurricane in 1970 that may have killed half a million people in what is now Bangladesh.

But even if we don't yet see "superhurricanes," evidence is emerging of a human fingerprint in the rising number of stronger, longer-lasting hurricanes. It is not yet proof of a long-term global trend tied to global warming, but the striking finding from both Emanuel and Webster that there is a consistent, global connection between rising sea surface temperature and rising storm strength is strong evidence of such a link. Whatever the theoretical concerns, for now it seems that, as the climatologist Kevin Trenberth, of the National Oceanic and Atmospheric Administration, puts it: "High sea surface temperatures make for more intense storms." In a paper published in June 2006, Trenberth calculated that about half of the extra warmth in the waters of the tropical North Atlantic in 2005 could be attributed to global warming. This warming, he said, "provides a new background level that increases the risks of future enhancements in hurricane activity."

One puzzling question is how scientists have until now failed to spot the sharply increased destructiveness of modern hurricanes. There is no dispute that, taken together, hurricanes have been doing a lot more damage in recent years. In badly organized countries, such as many in Central America, that has often meant a heavy loss of life. Elsewhere, if evacuation systems work, it has simply meant a huge loss of property. Insurance claims for hurricane disasters have been soaring for some years.

The prevailing view has, until recently, been that the problem is one of bad planning, rising populations, and more people putting themselves in harm's way. The beach resorts along Highway 9o and the large squatter colonies spreading along low-lying coastal land in Asia give some support to that view. But the new data suggest that there is more to it than that. A lot more. And that most of the extra damage is being caused by the storms themselves becoming more intense. The trend seems set to continue.

35

OZONE HOLES IN THE GREENHOUSE

Why millions face radiation threat

Joe Farman is a scientist of the old school. String and sealing wax. Smokes a pipe and drinks real ale. He has the faraway look in his eyes that you often see in men who have spent any length of time in Antarctica. He is retired now from the British Antarctic Survey, where he spent virtually his entire working life in a worthy though less than exalted capacity. Or he did until 1985, when he wrote one of the decade's most quoted research papers. He is the man who discovered the ozone hole over Antarctica. And the way it happened-or, rather, almost didn't happen-is revealing.

A quarter of a century ago, Farman was in charge of the BAS's Dobson meter, which for many years had been pointing up into the sky measuring the depth of the ozone layer in the stratosphere from the BAS's base at Halley Bay, on an ice shelf off West Antarctica. For several years his bosses had been trying to halt the observations and bring the old instrument home. After all, they pointed out, nothing interesting had happened for years, and satellites orbiting Earth were by then measuring ozone levels routinely. Ground-based observations were deemed superfluous.

But Farman resisted, and in 1982, he noticed a series of unusual and abrupt fluctuations in the ozone readings, just after the sun reappeared following the long polar night. It happened again the following year.

"I asked the Americans if they had seen anything similar from their satellites," he told me later. "They said they hadn't. So I assumed that my old machine was on the blink." But he was intrigued enough not to leave it at that. He found another Dobson meter back in Cambridge, and took it south in 1984 to check the readings. It recorded the same thing-only more so. Farman's data were by now unambiguous. He was seeing a deep hole opening in the ozone layer over the base. It lasted for several weeks before closing again. "We were sure then that something dramatic was happening," Farman said. In places, more than 9o percent of the ozone was disappearing in what appeared to be runaway reactions taking place in just a few days.

The ozone layer protects Earth's surface from dangerous ultraviolet radiation from the sun. Without this filter, there would be epidemics of skin cancers, cataracts, and many other diseases, as well as damage to vital ecosystems. Life on Earth has evolved to live under its protection, and would find things much harder without it.

For more than a decade, scientists had been concerned about the ozone layer, fearing that man-made chemicals such CFCs in aerosols might cause it to thin. But nobody had thought of a hole forming. Least of all over Antarctica, which was as far from the source of any ozone-destroying chemicals as you could get. And certainly not in a runaway reaction over just a few days. Earth was simply not supposed to work that way.

Farman bit his pipe and got to work. No more checking with NASA. He had his data and was intent on an urgent publication in the scientific press. Perhaps he sensed it was his moment of fame. He was certainly scared by what he had found-scared enough to miss all the office parties in Cambridge in 1984 to finish his paper titled "Large Losses of Total Ozone in Antarctica." He posted it to Nature on Christmas Eve.

The editors didn't quite share Farman's sense of urgency. It took them three months to accept his paper, and another two months to publish it. When the paper finally appeared, NASA scientists were confused. They still had no inkling of anything amiss over Antarctica. But they could hardly ignore the findings of two Dobson meters, however ancient. They re-examined the raw data from their satellite instruments and were shocked to find that their satellites had seen the ozone hole forming and growing over Antarctica all along, even before Farman had spotted it. But the computers on the ground that were analyzing the streams of data had been programmed to throw out any wildly abnormal readings. And the data showing the ozone hole had certainly fitted that category. The episode, as Farman was not slow to point out, was a salutary lesson for high-tech science. It was also a triumph for the string-and-sealing-wax school, and for the dogged collection of seemingly boring and useless data about the environment.

Paul Crutzen-who had unraveled much of the complex chemistry of the ozone layer-swiftly tied Farman's findings to specific chemical reactions involving CFCs that took place only in the uniquely cold air over Antarctica each spring. Below about -13o°F, unique clouds form in the stratosphere above Antarctica. These are called polar stratospheric clouds. It turned out that the runaway reactions happened only on the surface of the frozen particles in these clouds. The reactions required both the cold to create the clouds and solar energy to fuel them. And there was a window of a few weeks when both were supplied-after the sun had risen, but before the air warmed enough to destroy the clouds. After that, the air warmed and the ozone recovered, though the repair job took some months.

Farman's discovery and Crutzen's analysis finally pushed the world into taking tough action against ozone-eating chemicals. The Montreal Protocol was signed in 1987. Slowly, very slowly, the amount of CFCs and other ozone-eaters in the stratosphere is declining. And the Antarctic ozone layer is equally slowly starting to heal, though it could be a century before it is fully repaired, even if every promise made by government negotiators is met. But it had been a close call.

And things could have been a lot worse. "Looking back, we were extremely lucky that industrialists chose chlorine compounds, rather than the very similar bromine compounds, to put in spray cans and refrigerators early in the last century," says Crutzen. Why so? Bromine compounds make refrigerants that are at least as effective as their chlorine equivalents. But atom for atom, bromine is about a hundred times better than chlorine at destroying ozone. Pure luck determined that Thomas Midgley, the American chemist who developed CFCs, did not opt for their bromine equivalent. "It is a nightmarish thought," says Crutzen, "but if he had chosen bromine, we would have had something far worse than an ozone hole over Antarctica. We would have been faced with a catastrophic ozone hole, everywhere and at all seasons during the 197os, before we knew a thing about what was going on."

The world has been very lucky. Or has been lucky so far. The same com bination of low temperatures and accumulating gases that combined so devastatingly over Antarctica can also occur over the Arctic in some years. The conditions are not quite so favorable for ozone destruction, because the atmosphere is not quite so stable and the extremely cold temperatures occur less frequently. But there have been some near misses.

One occurred in January 2005. Anne Hormes, who runs the German research station at Ny-Alesund, in Svalbard, told me the story when I visited there a few months later. Temperatures in the lower stratosphere above Svalbard had for a few days fallen to -144°F, fully 14 degrees below the threshold necessary for the formation of polar stratospheric clouds, and extremely low even by the standards of Antarctica. "We feared that a real, big ozone hole would form," she said. `And if the temperature had stayed that cold for a few more weeks, till the sun came up to drive the chemical reactions, we would certainly have seen one." It would have been the Arctic's first full-fledged ozone hole, and in all probability a major world environment story.

Her concern is shared. The ozone expert Drew Shindell, of the Goddard Institute for Space Studies, says: "Overall winter temperatures are going down in the Arctic stratosphere-2005 was very cold. But actual ozone loss is very time-critical. So far, we have been lucky." But he doubts that our luck will hold. How so? Why are the risks of an ozone hole still growing, even though the chemicals that cause it are now in decline in the stratosphere?