JUDY WOODRUFF: As Florence was closing in on the Carolina coast this week, the size
of the threat it posed rekindle the discussion about the role of climate change in today's
weather patterns, and how it may be intensifying this storm and other past hurricanes.
Amna Nawaz joins that conversation for us now.
AMNA NAWAZ: The question is a vital one, with more and more people living along the coast
and the seaboard, which many say is a problem in and of itself.
And there is certainly some debate among scientists about how climate change impacts a storm.
But, increasingly, researchers are trying to explain the connections immediately after
a storm hits.
And they say climate change is definitely associated with both sea level rise and rising
temperatures.
To help walk us through some of the latest thinking and science around this, I'm joined
by Radley Horton of Columbia University.
He's a climate scientist at Lamont-Doherty Earth Observatory.
Radley Horton, welcome to the "NewsHour."
Let's start with the million-dollar question we face every hurricane season: What is it
we can say definitively about the link between climate change and these kinds of hurricane?
RADLEY HORTON, Lamont-Doherty Earth Observatory: Well, there's a very clear link.
And there's really three dimensions to it, to the way that human activities have increased
the risks associated with these types of storms.
The first is because climate change and warming has increased sea levels.
And, as a result, whenever any storm hits, water levels are that much higher, just by
virtue of that baseline having been raised, that gradual change in sea level.
That means more area flooded when a storm happens, and deeper, and therefore more perilous
waters associated with that flood.
The second component is the amount of rainfall associated with a given storm.
As we have warmed the atmosphere, as we have warmed the upper ocean, it can now hold more
moisture.
So, for a storm of a given strength, there's that much more moisture available to fall
out in the types of catastrophic rains that we're seeing here.
The third element, which is a little less certain than those first two, is that the
storms themselves can become stronger with climate change, the actual strength of the
winds, the depth of the low pressure.
The balance of evidence suggests that the major hurricanes are going to become a little
more frequent, a little more intense, as we further warm the atmosphere.
That one's not 100 percent a sealed deal, though, at this point.
AMNA NAWAZ: So, let's look back at one example from last year, for example, Hurricane Harvey.
It caused such widespread devastation.
That formed over the Gulf of Mexico, right?
You're talking about those rising sea levels and the warming of temperatures.
Reportedly, back then, the waters were just one degree Celsius warmer than average.
So we are to understand that just that one degree can mean that much of a dramatic difference
in a storm?
RADLEY HORTON: One degree matters a lot, especially when those ocean temperatures are already
really high to begin with.
You increase the temperature a little bit, the air can hold a lot more moisture, which
leads to -- when we think about our infrastructure, which has a rate at which it can drain, and
a little bit more rainfall can mean a lot more flooding.
And, paradoxically, or, in combination, as you raise sea levels for a given amount of
rainfall along the coast or inland, it's that much more difficult for that water to drain
out to the ocean if you're having a storm surge, and especially with that average sea
level essentially pushing some of that rainwater back on land, making it harder for to drain.
AMNA NAWAZ: So, walk me through a what-if scenario.
We're seeing Hurricane Florence batter the Carolina coast right now.
What if climate change wasn't an issue?
How would this one storm be different?
RADLEY HORTON: So, if we went back, say, 100 years or so, sea levels in this region would
have been a foot or so lower than they are today, primarily because of the absence of
those greenhouse gas emissions.
That means that less area would be getting flooded.
And that means that the depth of the water, which poses that risk of loss of life, extreme
damage to infrastructure, would have been a bit less.
Some homes, some assets, some people at those margins, if the waters are seven inches a
foot lower, that's a big part of the story.
And then there are these other dimensions to.
If you had a little bit less rainfall falling in the past, you would have less risk as well.
Of course, there are the other things humans are doing as well in some of these regions,
people moving into high-risk areas and removing natural surfaces that had been able to absorb
some of this rainwater, replacing them with pavement in some cases.
That also can exacerbate some of these risks.
AMNA NAWAZ: I have got to ask you about this as well.
Despite the overwhelming scientific consensus, there is a group of people, some very powerful
voices among them, who simply say that climate change is a hoax, right?
And they cite sometimes examples like the fact that, after Hurricane Katrina in 2005,
we went nearly a decade without a major hurricane hitting the U.S.
They also cite the downgrading of storms, like this recent one even just with Florence,
which has been downgraded in the last couple of days, to say, everyone hypes up the storm,
the media hype up the storm, it advances the climate change agenda is what they call it.
What do you say to that?
RADLEY HORTON: Climate change is about shifting risk.
If you look at one storm, one small region in just a few years, there's always going
to be that natural variability.
But what climate change is doing is, it's loading the dice.
And if you're a coastal planner or if you're someone thinking about assets and investment
along the coast, the risks are already changing.
The frequency of these coastal flood events are becoming much more frequent.
You're always in any individual place going to have runs of a few years of below normal
storms, below normal temperatures.
But the key point is that climate change has shifted these statistics.
We are getting much more frequent and more severe flooding, much heavier rain events.
And we're now getting about twice as many record-breaking extreme heat events as extreme
cold.
The statistics are shifting.
We need to plan for this, the shifting future.
AMNA NAWAZ: Radley Horton of Columbia University, thank you very much.
RADLEY HORTON: Thank you.