The impacts of global warming
on people are going to be more than just
the average change in the temperature. It's like a fever.
If you have a fever of 104 F (40C), what you feel is
a lot more than just a couple of extra degrees of warmth.
What you feel is your head hurts, and your stomach hurts, and you're sick.
It's more than just the temperature.
On the Earth, the strongest climate impacts are likely to be
regional impacts, rather than a globally averaged change.
It's kind of like if you have a log that's on fire and you increase
the amount of oxygen, you can kind of predict overall that the log will
burn faster in some way.
But what's actually affecting a little bug crawling on the log
is the flickering of the flames,
and that's a lot harder to forecast.
I have my students a book by Mark Lynas
called Six degrees, Our Future on a Warmer Planet.
The book is divided into chapters
that correspond to different amounts of warming.
And he's describing the various climate impacts
that people have predicted, scientists have predicted,
as a function of the amount of warming where they start to kick in.
If you're interested, I recommend you have a look at that.
I think the most severe impacts are likely to have
to do with water availability and drought.
It's a bit paradoxical.
Overall, when you make the planet warmer, warmer air can hold more water vapor.
And if you're running the air through the wringer of
the hydrological cycle, of having it go up, and make clouds,
and come back down, and from that you get an increase in the overall amount of rainfall
as the earth warms. But as it turns out, places that are
dry today are predicted to get even drier in a global warming a world.
A continental interior dries out as the temperatures go up.
In continental interiors
there is expected to be a deficit of rainfall relative to the
pre-warming a case. Here is a plot of
a map of where the rainfall changes are
expected to be found, a composite from all of the different climate
models that are used in the IPCC scientific assessment.
And it's hard to predict regional climate
changes, which means that different models don't
always agree exactly on what they expect to have happen here or here or there.
But there is some coherence that's coming out from the models.
What you see is drying in places where it's actually
anomalously dry today. The American Southwest, the
Mediterranean, Australia; these are all places that are drier
than they should be today.
And they are predicted to get even drier in a warmer world.