You’ve probably heard that weather is getting more extreme and that this is in part because
accumulating greenhouse gases have caused the air at earth’s surface to warm by an
average of 0.8 degrees celsius over the last century. But how could a barely perceptible
rise in air temperature lead to such crazy changes in weather?
Well, that air temperature rise actually only amounts to 1% of the extra energy absorbed
by earth’s atmosphere over the last century – a few percent has been absorbed by land
and almost all the rest has been soaked up by the oceans. That increase in ocean heat
content is the energy equivalent of an atomic bomb exploding every second for the last 100
years. And THAT matters because heat stored in the oceans has a big impact on the weather.
For one, the warmer the water at the surface gets, the more of it vaporizes into the air.
At the same time, every degree increase in air temperature raises the air’s capacity
to hold water vapor by about 7 percent. This means parcels of air out over the ocean are
picking up more water than they used to, which leads to HEAVIER rains and snows. Meanwhile,
warmer land surfaces mean parcels of air over land are also picking up more water than they
used to, making dry places drier and droughts harsher.
Warmer oceans also make concentrated hot spots on the ocean’s surface even hotter. These
areas of high sea surface temperatures have always helped drive the biggest storms and
floods, including, in recent years, both Hurricane Sandy and super-typhoon Haiyan. We don’t
yet know for sure whether warming oceans are producing a greater number of these storms,
but it’s basic physics that more heat in the oceans gives these kinds of storms significantly
more energy and destructive power when they do happen.
So if you’ve heard that the world’s weather has been getting more extreme, it’s not
just a lot of hot air. It’s also a bunch of warm water.