Hurricanes: Is This the Calm Before the Storm?

America’s response to the threat posed by Hurricane Floyd was exemplary. Faced with satellite images of one of the largest and most powerful Atlantic hurricanes ever seen, governments ordered the largest peacetime evacuation in U.S. history.

Fortunately, Floyd’s track shifted slightly to the north and much of the storm’s energy dissipated over colder water before it made landfall in North Carolina. Things could have been far worse. Last year, Mitch slammed into Central America, killing 10,000 unprepared people. In 1992, Andrew caused almost $26 billion in damage.

While most evacuees sighed with relief, a disgruntled resident of Jackson Beach, Fla., complained, with 20-20 hindsight, “If we can put a man on the moon, why can’t we predict the path of hurricanes?”

It turns out it is harder to predict hurricanes than it is to send astronauts to the moon. There are far more variables involved in the circulation of the Earth’s atmosphere than there are in a moon shot.

What we do know about hurricanes suggests that Floyd, Mitch and Andrew could be harbingers of more to come. Hurricanes get their power from the energy contained in warm, moist air over tropical oceans. They form only where sea-surface temperatures are above 80 degrees Fahrenheit, and their maximum destructive potential increases with increasing sea-surface temperatures.

The world is getting warmer and wetter. Global temperatures have increased by about one degree over the last century, and the warming has accelerated during the last two decades. The 10 hottest years on record have all occurred since 1980. Last year was probably the hottest this millennium. Warming increases evaporation, intensifying both droughts and floods. The link between these facts and the increasing pollution of the atmosphere with carbon dioxide and other heat-trapping gases is still disputed by die-hard skeptics, but their ranks are dwindling.

If global warming continues unchecked, we may look back on the 1990s as the calm before the storm. A study by MIT scientist Kerry A. Emanuel suggests that global warming could increase the maximum destructive potential of hurricanes by 40%-50% by the middle of the 21st century. While many factors can prevent hurricanes from forming or prevent them from reaching their maximum potential intensity, recent studies by scientists at the National Oceanic and Atmospheric Administration and the Max Planck Institute for Meteorology in Germany predict that the incidence of intense hurricanes will increase with global warming.

These predictions are not easy to confirm. Because intense hurricanes are extreme events, it’s difficult to detect trends. According to the National Hurricane Center, there were 33 hurricanes from 1995 through 1998, the most ever for a four-year period, despite 1997 being an average year. Furthermore, insurance payouts for weather catastrophes are at an all-time high. Part of this is due to population growth in vulnerable areas and increased property values, but some of the world’s largest insurance companies, like Munich Re and Swiss Re, believe that damage is on the rise, even controlling for these factors. Nonetheless, studies looking for long-term trends in hurricane frequency using the limited data available have been inconclusive.

There is increasing evidence of a relationship between the incidence of hurricanes and El Nino. The 1997-98 El Nino was one of the most intense on record. This phenomenon, due to the buildup of warm water in the Pacific, influences weather patterns around the world by intensifying and redirecting the high-altitude winds known as the jet stream. El Nino played a substantial role in last year’s wacky weather, particularly the downpours that wreaked havoc in California during winter-spring 1998.

El Nino has a friendlier effect in the Atlantic, however, reducing the incidence of hurricanes because strong jet-stream winds make it more difficult for thunderstorms to coalesce into large-scale cyclones.

The flip side of El Nino, known as La Nina, has the opposite effect. The jet stream is less intense and farther north, leaving ideal conditions for hurricanes to form in the tropical Atlantic. Toward the end of last year, El Nino gave way to La Nina, paving the way for Mitch and Floyd. How will global warming influence the El Nino-La Nina cycle? This is an area of active research. Some studies find little relationship, but El Ninos would still be more intense because they would come on top of a warmer baseline. Other researchers believe global warming could cause a kind of permanent El Nino, bad news for the West Coast and much of the rest of the world, but good news with respect to the frequency of Atlantic hurricanes. Most troubling are studies, such as the one by Mojib Latif of Max Planck, that suggest the cycle itself will intensify, implying that both El Ninos and La Ninas would become stronger. Though this may sound strange, it is plausible: If you give a swing a hard push, both the upswing and backswing will be higher.

Even if the frequency of hurricanes does not change, damage is likely to increase. This is partly due to the additional energy and moisture added to the atmosphere by global warming. In addition, sea levels are rising, as ocean water expands and as glaciers melt. This implies that storm surges created by hurricanes, which often do most of the damage, will come on top of seas that are a foot to three feet higher than today. Since one foot of sea-level rise can cause more than 100 feet of coastal retreat, this synergy is extremely powerful. Sea-level rise is predicted to double the global population at risk of flooding, from 46 million to 92 million.

Meanwhile, more and more people are moving into harm’s way. More than half the U.S. population live within 50 miles of the coast, and that percentage is increasing. Similar trends are found around the world, leading the International Federation of Red Cross and Red Crescent Societies to predict an era of superdisasters. Last year, declining soil fertility, drought, flooding and deforestation created 25 million environmental refugees, more than wars and conflict, according to the Red Cross. “Everyone is aware of the environmental problems of global warming and deforestation on the one hand, and the social problems of increasing poverty and growing shantytowns on the other. But when these two factors collide, you have a new scale of catastrophe,” said Astrid Heiberg, president of the International Federation.

In response to warnings that a massive storm was bearing down on us, governments and citizens responded swiftly and effectively. Damage from Floyd was minimized by a combination of precautionary action and good luck. Though the time frame is years rather than days, we have been put on notice of the threat from global warming. We can’t count on our luck holding. It is time to respond and begin reducing global-warming pollution. *