(Bryce) One of the strongest connections between climate change and extreme weather is water vapor,
the most abundant greenhouse gas. Something Dr. Jennifer Francis explained to me
in our full conversation. (Dr. Francis) As the air
gets warmer it can hold more water vapor in it,
and as the oceans get warmer they're evaporating more water into the atmosphere. So we're seeing
a very clear increase in the amount of water vapor that's in the atmosphere. Globally speaking it's
about a seven percent increase in the amount of water vapor since the 1970s or so. The reason that
water vapor is so key is that it plays a number of roles in both the climate system, and also
in weather patterns. Water vapor is actually the most important greenhouse gas in the atmosphere,
and so as we increase the amount of it, it's adding to the heat that's being trapped by
the human caused other greenhouse gases. So it's exacerbating the global warming problem.
It's also the source of energy for storms. When water vapor - which is a gas - condenses
into a liquid form, which you see as a cloud, it releases heat into the atmosphere. And that heat
is what storms feed off of to generate their strong winds and you know all the other impacts
of storms. And then of course that extra water vapor can also produce more precipitation.
And so we're seeing a very clear increase in the frequency of heavy precipitation events,
and these are not small increases. We're talking about 50% and higher increases in these very
heavy downpours, heavy snowstorms. We're clearly seeing the impacts of this already and there's
no doubt that it's connected to this increase in the amount of water vapor in the atmosphere.
(Bryce) Higher temperatures combined with more humid air are pushing conditions beyond
what the human body can naturally endure in more and more places around the world.
The point you made in your talk about the health dangers that come when it doesn't cool
off enough at night time was really important. (Dr. Francis) Sure. So on the right side of this
graph is showing the fraction of the land in the United States where temperatures have been extreme
during the day time. You know we can see there was a very warm period back in the 30s and 40s, you
can think about the big dust bowl out in the west that happened during that period. But then again
in the recent years we're seeing these big spikes again in the daytime maximum temperatures. But on
the left side of the graph, as you said, we're seeing a much bigger impact during the nighttime
temperatures. And the reason this is so important is because you know people are trying to sleep
at night, obviously, and if their bodies aren't able to cool off sufficiently through sweat,
or if you don't have air conditioning or some other way to cool yourself off, then there is a
actual physical threshold where if it doesn't cool off enough combined with extra humidity that's in
the atmosphere - that we know is also happening - then your body just can't really get rid of
the extra heat that it produces just through normal processes. So we're seeing this happen
in many places around the globe now where it's just too hot to survive at night.
(Bryce) Your system shuts down. When that heat index figure goes through the roof,
especially in the equatorial zones, there will be, what, whole months when you won't
be able to really work at all--if you don't have an air-conditioned building.
(Dr. Francis) Exactly right. And you know that you can pretty easily jump to thinking about
migration-areas where people are already suffering mightily.
And it's not just their own discomfort, but also agricultural conditions aren't suitable anymore to
growing crops. You've got people who just have no way to live: they're suffering health-wise and so
they're looking for somewhere else to go. And it's very likely we're going to see migration of large
numbers of people that are going to make today's immigration issues look like almost nothing.
And there's clearly - I think - a climate factor. And people are starting to quantify that. So
it's not just the heat, per se, but also drought. And drought has already been
implicated as a major factor in the Middle East and a lot of the issues that are occurring there.
(Bryce) In a recent talk, Dr. Francis previewed the extreme temperatures
coming soon to the United States so. (Dr. Francis) So this is the number of days above
100 degrees (F) that are projected for the middle of the century, and by the end of the century.
Huge sections of this country - if we stay on the path we're on - will be almost unlivable
and will require a lot more energy just to be able to live in those areas. But agriculture,
it's going to have a hard time. (Bryce) We can expect warming, combined
with more water vapor, to essentially shift the entire climate north by about 1,000 miles. Meaning
the northeast, for example, will experience the kind of weather South Florida experiences today,
and Miami will feel like the stifling hotbox that is the equatorial rainforest of South
America. That's over 1,000 miles of shift. (Dr. Francis) Right, and that's just the average
temperature. It's about a nine degree warming for Providence area, so New England. Basically,
their the average temperature is going to feel more like what Florida is experiencing now.