An obese, middle-aged man is running to catch a bus. Suddenly, he clutches his chest, falls to the ground and dies of a massive heart attack. It turns out that he's a smoker and a diabetic, has high blood pressure, eats a diet high in saturated fat and low in leafy green vegetables, pours salt on everything, drinks too much beer, avoids exercise at all costs and has a father, grandfather and two uncles who also died young of heart attacks.
So what killed him? Most people are savvy enough about health risks to know this is a trick question. You can't pick out a single cause. His choices and his genes all contributed to the heart attack — but you can say with confidence that the more risk factors that pile up, the more likely it is to end badly.
Somehow, though, people think that it makes sense to ask whether a given extreme weather event — a devastating heat wave or a punishing drought or a deadly torrential rainstorm — is caused by climate change.
That's a trick question too. Scientists know that the increasing load of greenhouse gases we're pumping into the atmosphere doesn't "cause" extreme weather. But it does raise the odds, just as a diet of triple bacon cheeseburgers raises the odds of heart disease.
The floods that have been threatening to inundate Bangkok, Thailand, for nearly a week now are a perfect example. Since last summer, torrential rains have been pounding the Thai highlands, swelling the country's rivers, including the Chao Phraya, which flows through the capital. Many people have fled for drier ground, fearful that the city's dikes might not hold back the water — especially over the weekend, as the virtual tsunami from the north tried to empty into the Gulf of Thailand just as unusually high tides were pushing up the river. "It seems like we're fighting against the forces of nature," Prime Minister Yingluck Shinawatra told the New York Times last week.
That's partly true. But as experts in risk management have come to realize, it's not just nature that has put coastal cities like Bangkok in the cross hairs of catastrophe. Monsoons and floods have drenched Asia for thousands of years. But before cities like Bangkok, Jakarta, Manila and Kolkata (formerly Calcutta) arose, climate-related disasters affected relatively few people.
Now, as the latest edition of the Climate Change and Environment Risk Atlas from Maplecroft, a London-based risk assessment firm, makes clear, swelling populations and shaky infrastructure, especially in poorer nations, put millions in harm's way.
The very existence of mega-cities, then, is one risk factor for weather and climate disasters (the Bangkok metropolitan area holds nearly 15 million people) — it's the high blood pressure, you might say, of disaster.
But climate change is an additional risk factor. Scientists have shown that torrential rains have gotten heavier in recent years, in large part because of human-caused global warming. This year's Southeast Asian monsoon may or may not have the fingerprints of climate change all over it, but in general, the trend toward heavier rains is likely to continue. Last weekend's high tide doesn't have anything to do with rising sea level; it was caused by an unusual alignment of Earth, moon and sun. But as climate change does raise sea levels over the coming century — by an average of 3 feet by 2100, according to the current best estimate — rain-swollen rivers will have a harder and harder time emptying quickly into the ocean.
But wait, (as they say on infomercials) there's more! Another consequence of climate change is that hurricanes and typhoons may get more intense, fueled by warmer ocean waters. That means stronger storm surges will be pushing on higher seas and driving them farther inland — and as survivors of Hurricane Katrina know very well, it's not so much the winds and rain that get you; it's the surge.
This time, it's Thailand's turn to have a heart attack. Last summer, it was Texas and Oklahoma, with parching drought and the hottest summers on record. In the fall, it was Vermont and other parts of the Northeastern U.S., inundated with devastating rains and floods. A couple of weeks ago, it was Central America, where nearly 5 feet of rain fell in 10 days, causing deadly floods and mudslides. This week, it was the Northeast again, hammered by the sort of storm that normally holds off until December or even later.
All of these disasters might have happened in any case, for purely natural reasons, just as people without any obvious risk factors sometimes have heart attacks. But with the extra factor of human-generated climate change added to the mix, the odds of a bad result are just that much higher. And if we keep adding greenhouse gases to the atmosphere, those odds will keep on rising.
By Michael D. Lemonick, a senior writer for Climate Central, a nonprofit science and journalism organization in Princeton, N.J.