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Posts Tagged ‘Hurricane Irma’

Has Global Warming Made Hurricane Damage Worse?

Sun ,31/12/2017

Hurricanes are the most violent and destructive storms in nature. There’s a smaller, yet potentially destructive, storm raging between climate scientists and climate skeptics about the nature of hurricanes. The scientific evidence points to the fact that global warming  causes hurricanes to be more intense. Skeptics would like to convince everyone that global warming has not made any change in hurricanes, so there is no need to address global warming. Skeptics do have a point or two, but not many. Skeptics want absolute proof from the scientists, but science doesn’t work that way. The changes caused by a warming world have changed the probability of the occurrence of extreme weather events, and skeptics apparently don’t want to consider probabilities.

Skeptics say that the number of hurricanes in the Southern Atlantic is not increasing, and they’re probably right on that. Hurricanes begin as tropical storms, which occur at random depending on the weather conditions. Skeptics also say that the increasing economic damages done by hurricane is because of the increased construction along the coasts. That is partly right, but it is also right that the damage done by storm surges has increased because of increased sea level rise, which is a measurable consequence of global warming. Those who listen to the skeptics, and unwisely build in floodplains, are sure to experience more damage from storm surges.

Global warming has made the oceans much warmer, even later into the year. The water temperature must be above 82°F for a tropical storm to grow into a hurricane, and the warmer the ocean the more likely it is that the a hurricane, once formed,  will intensify. Hurricanes are much like a heat engine, they are driven by the warm air rising from the oceans much like a chimney effect. The greater the temperature difference between the ocean and the upper atmosphere, the faster the flow upward and the greater the wind speeds.

If you could slice into a hurricane, it would look something like the diagram below. It has a low pressure eye at the center, and the air drawn into it rises and circulates counterclockwise around the low pressure area, faster and faster as it nears the eye. The small red arrows show warm, moist air rising from the ocean, and forming bands of clouds around the eye. As the warm moist air produces rain, more heat is released, warming the air further and causing it to rise faster until it reaches the top of the storm. Reaching there, it has become cooler and dryer. The blue arrows show how the cool, dry air then sinks in the eye and between the bands of clouds. Remember that the bands of clouds are rotating very quickly, and the large red arrow show the rotation of the rising bands of clouds.

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A hurricane is much like a heat engine. It is driven by the energy from the warm oceans and the cold temperature of the atmosphere above the storm. Because of global warming, that temperature difference is greater. The upper atmosphere receives its energy from the earth below. The increasing carbon dioxide between acts as a blanket, which causes the oceans to be warmer and the upper atmosphere to be colder. As in all heat engines, the greater the temperature difference, the more power the engine has. As a hurricane passes, it leaves the oceans cooler behind it as it sucks energy from the ocean. Because of global warming, the warmth goes deeper there is a greater area of warm water,  both factors which provide more heat to the hurricane and cause it to increase in size and intensify.

The vapor pressure of water increases exponentially with temperature. In our warmer world, there is now 10 to 15% more water vapor in the rain bands moving around the hurricane. When hurricane Harvey made landfall over Houston, it could be expected that Houston would receive increased rainfall. But by chance, Harvey stalled  over Houston and continued to pull warm moist air in from the Gulf, dumping over 50 inches of rain. Sea level rise has been measured to be about 30 inches along the Gulf Coast. The extreme rainfall coupled with the sea level rise  increased the storm surge and flooded much of the lower areas of Houston. The storm’s stalling was a chance event, and the skeptics are right when they say it should not have happened, but it did. Considering the storm’s intensity, the wind damage, the sea level rise, and the extreme rainfall, climate scientists attribute about 30% of the damage in Houston to global warming.

Below is a satellite image of hurricane Irma on the right, compared in size to the smaller hurricane Andrew which struck Florida in 1992, killing 65 people, destroying 65,000 home, and doing $26 billion in damages. Andrew was the  the most destructive hurricane to hit Florida ever before, and Irma could have been much worse.  

 

Florida was extremely lucky that hurricane Irma, wider than the whole Peninsula, went up the western side of the Peninsula. The western side of the  Peninsula experienced very little storm surge. The winds on the leading edge of the Irma, circulating counterclockwise, blew the ocean water away from shore, leaving the ocean dry for several hundred yards out as it passed. The storm was so weakened that by the time the back of the storm made landfall, directing the water toward shore, that the storm surge was only a few feet. Had Irma gone up the east side of Florida, the storm surge at the leading edge of the hurricane could have been as much as 15 feet, completely inundating much of Miami.

There you have it. Global warming has increased the temperatures of the oceans and has increased the temperature difference between the oceans and the upper atmosphere, both factors which tend to make the hurricanes more intense. The warmer oceans put more moisture into the air, making the rainfall from the hurricanes greater, and sea level rise has increased the height of the destructive storm surges. This fall, there were five intense hurricanes which formed in the Southern Atlantic, all of them making landfall and doing extensive damage. That could just be a chance occurrence, as the skeptics claim, but it has never happened before.

(c) 2017 –  J.C. Moore