Hurricanes

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40 years ago in the United States, Kerry Emanuel became a registered Republican. As an undergraduate at MIT in the 1970s, his classmates’ far left, pro-communist views horrified him. Today, politically, not much has changed for him. He still thinks highly of conservative icons, like Ronald Reagan. He still mostly votes Republican. But Dr. Emanuel also happens to be the Cecil & Ida Green Professor of Atmospheric Science at MIT. He is a leading expert in the field of hurricane research. And he now gets email threats from other conservatives. Because Emanuel doesn’t just study hurricanes. He studies the ways in which human-caused global warming can make hurricanes more destructive in a warmer world. How did a conservative undergraduate end up as the face of global warming’s impact on hurricanes? By following the science.

One of the most damaging effects of hurricanes is their storm surge

The science of hurricanes tells us rising sea levels, heavier rains, stronger winds, and warmer ocean water will grow stronger as we warm the planet. One of the most damaging effects of hurricanes is their storm surge. Hurricanes’ powerful winds pile up enormous volumes of water. The low pressure of the center of hurricanes lets the ocean level rise higher. Together, they create a towering supply of water. Waves ride on top of this surge. In a world without climate change, hurricanes still produce storm surges. But as we continue to heat up the planet, we cause sea levels to rise. This increase in the underlying sea level makes the storm surge from hurricanes even larger in a warming world. That means storm surges can do more damage over the same area, and reach areas even further inland than before. A recent report by Lloyd’s of London, an insurance firm, looked at the effect of sea level rise and Hurricane Sandy.

They estimate that the relatively small amount of sea level rise we’ve had increased Sandy’s damages by 30%. Or around $8 billion USD in New York alone. In addition to storm surge, hurricanes produce torrential rains. The warm, moist air they pull up from the ocean cools and condenses as it rises, causing massive rainfall. As we warm the planet, the heavy rains from hurricanes are expected become even heavier. These rains drench coastal areas, which combines with the storm surge to cause massive flooding. Hurricanes are also destructive because of their fierce winds. As we continue to warm the planet, the maximum wind speeds of hurricanes are expected to get even faster. Hurricanes form in the tropics for a reason. They depend on hot ocean temperatures relative to the coolness of the air above.

A warmer world will have stronger but fewer storms

As we warm the climate, this can provide more fuel for hurricanes, making them more powerful[CL3] . Studies looking at this question using many different methods have begun to converge on agreement about this. A warmer world will have stronger but fewer storms. Not all of the changes to hurricanes in a warming world may make them worse. If ocean temperatures are hurricane fuel, wind shear is hurricane kryptonite. Wind shear is just the difference in wind speed at different heights in the atmosphere. When wind speed is pretty much the same down low as it is higher up, hurricanes can grow strong. When wind shear is high, that is, when wind speeds are different, hurricanes get ripped apart. As humans warm the planet, some places where hurricanes form may see an increase in wind shear. That means that for those areas, hurricanes may grow more intense, but also break up more often as they try to form. So we may see somewhat fewer, but more powerful storms overall. Hurricanes are also pushed around the ocean by prevailing winds.

These steering winds might also change as we heat the planet. For some areas, that might mean more storms get pushed away from land. For other areas, that might mean more storms make landfall. But this too remains an area of active research. But climate skeptics reject even the most solid links between climate change and hurricanes. They say that hurricanes have always happened. They point to devastating storms that occurred in the past, when human influence on the climate was smaller than it is today. They point to short periods without major hurricane strikes as evidence that nothing is changing. They are sure- there is no link between global warming and hurricanes. A closer look at skeptics’ claims reveals that they don’t actual challenge the scientific links between warming and hurricanes at all. Rather, their claims rely on a number of fallacies common to science denial.

One of the most pervasive is oversimplification. Of course hurricanes, even terrifically powerful ones, have happened in the past. And sure, they’ve happened when greenhouse gas levels were much lower than they are today. But that’s not the whole story. We know that hurricanes are affected by a number of environmental factors. One of the strongest being is hot ocean temperature. Looking back over hundreds of years, we can see that hurricanes have gotten stronger in response to natural increases in ocean temperature. That strengthens our confidence that hurricanes will get stronger as humans warm the ocean relative to the atmosphere. It doesn’t weaken it. [CL4] Climate skeptics are fond of pointing to periods with low hurricane activity to deny a link with warming, while ignoring the bigger picture. This is a common science denial tactic called cherry-picking. They point out that in recent years the North Atlantic has not had as many dramatic storms as the mid-2000s.

However, the overall picture since we’ve had accurate observations points to an increase in hurricane activity. And that this increase is strongly tied to warming ocean temperatures. When we reconstruct storm activity over hundreds of years, we see a similarly close relationship. Based on such flawed reasoning, climate skeptics jump to a faulty conclusion. They draw the wrong lessons from what observations and history tell us about hurricane behavior. During his research, Kerry Emanuel has flown into the eye of a real world hurricane. And although his findings have put him in the middle of political storm, the science doesn’t care about politics. How hurricanes will change in a warming climate is an area of active research, but some links to warming have become clear. As humans warm the planet, rising sea levels, heavier rains, stronger winds, and warmer ocean water will increase the destructive potential of these massive storms.

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