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Hurricanes are one of the things 
that people think about the most. 

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Hurricanes are complicated. 

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They form from very 
specific "seed" weather events,

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particular kinds of winds, blowing 
of Africa. 

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and then, whether they grow into 

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a hurricane or not depends on real 
subtleties of 

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the atmospheric circulation, like the 
presence of 

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wind blowing in different directions at 
different altitudes, 

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which is called wind sheer, tends to break 
a storm apart 

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before it grows into a hurricane.

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There's not a real strong theory for 

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why we tend to have a certain number of 
hurricanes every year, 

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Some aspects of the climate 
change forecast

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are very easy, like a global 
average 

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temperature is constrained by 
large-scale energy considerations. 

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Regional climate changes are not so easy 
to get, and then things 

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like hurricanes are, really the 
devils down in the details, and 

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so it's hard to predict. 

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But making the sea surface temperature 
warmer is 

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thought to provide more power for the 
hurricane. 

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The hurricane derives its energy from the 
water 

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vapor that it gets from the water 
surface. 

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When a hurricane starts going over land, 

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it starts to decrease its intensity and 
die. 

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That's because it doesn't have access to 
the water vapor. 

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Making the sea surface temperature 
warmer is thought 

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to make hurricanes stronger. 

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On the other hand, making the upper 
atmosphere warmer would tend 

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to negate some of the impact of making the 
surface warmer. 

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And what is actually observed, 
is that the hurricanes 

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in the last few years seem to be getting 
stronger 

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even than simple theory would predict, 
based on thermodynamics 

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of the temperatures and 

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the heat engine that is a 
hurricane. 

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It's kind of a loose cannon in the 
forecast of what will happen in the future. 

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And there are reasonable and concerned 
people on both 

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sides of this question, it's not really 
well answered. 

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But the way that models respond to a 
change in temperature, is to shift the 

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frequency distribution of the hurricanes a 
little bit toward the stronger. 

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We have categories, category 
three, four and five hurricanes. 

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where the category five was just a little 
tail 

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of the distribution in the 
natural world. 

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If we shift this distribution this way 
suddenly the proportion 

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of them that are these category fives 
could go way up.