Tuesday, June 10, 2014

Global Warming and Tropical Cyclones

Tropical cyclones (hurricanes, typhoons and cyclones) get their energy from warm ocean water. As water vapor rises and condenses into liquid water it releases very large amounts of energy, which powers the storm. So, it is a natural assumption that as the oceans heat up, we should see some resulting effect in the formation of tropical cyclones. But, it isn't that easy. There are more factors in the formation of cyclones than just ocean temperature. Wind shear, in particular, is critical for the formation of cyclones. As a tropical depression starts to form, too much wind shear will blow the energy from condensing water away and will also deform the shape of the central vortex which makes up the eye of the storm, making it less likely a storm will form. Of course, global warming will have an effect on wind shear. And, there are other factors involved in storm formation, as well. So, we can't just say that as the sea surface temperature goes up we will see more and stronger storms.

But, what will happen is an important question and one that a lot of research is being done on. A paper published by scientists at Stony Brook University and MIT, appearing in the Journal of Advances in Modeling of Earth Systems described some recent computer model results. The authors modeled an idealized tropical climate and used cloud formation models to develop tropical cyclones on a supercomputer. As they varied the sea surface temperature from 21 degrees Celsius (70 degrees F) to 36 degrees Celsius (97 degrees F), they found that the size and strength of the cyclone increased as the temperature went up. At the same time, fewer storms were formed. A 6 degree Celsius (11 degree F) rise in temperature resulted in a doubling of kinetic energy in each storm as well as a doubling in the amount of precipitation.

How valid is the model? In fact, we have already seen these results taking place over the last 50 years.

Based on this computer model and the actual storm events over recent decades, what we can expect as global warming continues is fewer storms, but the ones that form will have stronger winds and more rain. Damage from storm surges will increase dramatically due to a combined effect of larger storm surges and rising sea levels.

Of course, guess who will get to pay for all of this damage? Hint: It won't be the fossil fuel industry.

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