Hurricanes are one of the things that people think about the most.
Hurricanes are complicated.
They form from very specific "seed" weather events,
particular kinds of winds, blowing of Africa.
and then, whether they grow into
a hurricane or not depends on real subtleties of
the atmospheric circulation, like the presence of
wind blowing in different directions at different altitudes,
which is called wind sheer, tends to break a storm apart
before it grows into a hurricane.
There's not a real strong theory for
why we tend to have a certain number of hurricanes every year,
Some aspects of the climate change forecast
are very easy, like a global average
temperature is constrained by large-scale energy considerations.
Regional climate changes are not so easy to get, and then things
like hurricanes are, really the devils down in the details, and
so it's hard to predict.
But making the sea surface temperature warmer is
thought to provide more power for the hurricane.
The hurricane derives its energy from the water
vapor that it gets from the water surface.
When a hurricane starts going over land,
it starts to decrease its intensity and die.
That's because it doesn't have access to the water vapor.
Making the sea surface temperature warmer is thought
to make hurricanes stronger.
On the other hand, making the upper atmosphere warmer would tend
to negate some of the impact of making the surface warmer.
And what is actually observed, is that the hurricanes
in the last few years seem to be getting stronger
even than simple theory would predict, based on thermodynamics
of the temperatures and
the heat engine that is a hurricane.
It's kind of a loose cannon in the forecast of what will happen in the future.
And there are reasonable and concerned people on both
sides of this question, it's not really well answered.
But the way that models respond to a change in temperature, is to shift the
frequency distribution of the hurricanes a little bit toward the stronger.
We have categories, category three, four and five hurricanes.
where the category five was just a little tail
of the distribution in the natural world.
If we shift this distribution this way suddenly the proportion
of them that are these category fives could go way up.