Science Forward-Climate Change

music Cynthia Rosenzweig: Climate change is the
planetary issue of our time, and the future. It’s also the issue in which human
beings finally realized that they were affecting everything. Flora Lichtman: It’s unusual for a scientist
to speak so unequivocally. It should give us some indication of the seriousness
of the challenge that we face with climate change. Despite
scientific consensus, there’s been a lot of political divisiveness
about climate change. In this video, we’re just going to focus on
the science. We’re going to walk through how we know that
climate is warming. We’re going to talk to a researcher who’s
studying past climate by looking at trees that are alive today. We’re
going to talk about climate modeling and how researchers verify
that their models are reliable. We’ll start with a look at carbon and its
natural cycle. The carbon cycle is the exchange of carbon between
living organisms and the inorganic parts of the Earth. What scientists have discovered is that humans
are interfering with the carbon cycle in a major
way. Cynthia Rosenzweig: Mostly we look back to
the beginning of the industrial revolution, because that’s when basically
our civilization changed. We began to power our entire society with
fossil fuel, which is burning stored carbon, which releases CO2. FLora Lichtman: We’ve all heard that more
greenhouse gases in the atmosphere, like carbon dioxide, warms the
climate. How does that work, exactly? Tom Koutavas: It turns out that these particular
substances or molecules that we call greenhouse gases, have the ability
to allow sunlight coming towards the Earth from the Sun to come
in unimpeded. They’re basically transparent to sunlight,
but they are relatively opaque to Earth light or Earth
radiation going back out, and so they capture that. In the process of
capturing and absorbing that, they warm up and they warm up the air
around them. What we’re doing right now with human activities,
unfortunately, is we’re adding to this natural greenhouse. You can
think of it as starting from something that is good, the natural
greenhouse, and adding to it. Adding and getting too much of a good
thing, if you like. FLora Lichtman: The hockey stick graph, so
called because of its shape, plots CO2 levels in our atmosphere and shows
that, for about the past 150 years, levels have been rising exceptionally
fast and continue to escalate. When researchers talk about climate change,
you often hear them refer to climate models that predict
Earth’s future climate. What is a climate model? Cynthia Rosenzweig: First of all, I have to
tell you what it’s not. Sometimes very young students, like high school students,
come, and they’ve heard that they’re going to work on the model.
So they come in and they start looking around for a terrarium.
laughs You know, one of those things that has like a closed…with
plants inside. Unfortunately, that is not what a climate
model is. A climate model is a set of mathematical equations
that solve the forces of our climate system that
represent and solve for the dynamic movement, heat relations and precipitation
falling down, what the oceans and the cryosphere are
doing. It’s all represented by equations and the
computer programs, when they hit the button to run a simulation,
are solving those equations across grid boxes covering the entire
globe. Flora Lichtman: How do we know we can trust
the models? “Replication of findings” says Rosenzweig. Cynthia Rosenzweig: There are now about 30
global climate models with groups of scientists all over the world doing the same
thing, and guess what? They differ somewhat in their ranges, because
they’re representing the processes. Those equations are slightly
different from the scientists around the world. Basically, all of the modelers, when they
do this experiment, they get the same result. That’s
really the fundamental heart of the climate change issue. Flora Lichtman: How do our observations of
weather fit with the climate change story? Take the winter of 2013, 2014. If it doesn’t
ring a bell, the words “polar vortex” may jog your memory.
It was one of the record books. Here in New York City, we suffered through
more than a month of sub-freezing temperatures and over 50 inches
of snow. How do we put this in context? Laura Broughton: You’ve probably heard a friend
say it was a really hard winter, there was a lot of snow, so obviously
there’s no climate change. The thing to remember about changes
in the overall climate is we’re not looking at individual events.
We’re looking at the long-term trends. We’re looking at the averages
over time. It’s really all about probabilities. When you start looking at the models, for
predictive models for what’s happening with climate change,
you have a higher incidence or higher probability of big events.
Really big storms or more extreme weather days. Flora Lichtman: Part of understanding how
climate is changing is comparing current climate to past climate. Systematic
weather records only go back 150 years, and the planet is 4.5 billion
years old. How do scientists get a sense for prehistoric climate? Tom Koutavas: They call it “Proxies” because
they are stand-ins, or surrogates, for something that we would like
to know more about. A temperature proxy is some kind of physical,
biological or chemical variable in a natural system that
is related to temperature itself. We measure the proxy.
Each proxy has a specific relationship with the target variable. It
might be temperature or it might be precipitation. Flora Lichtman: Plant fossils can give us
a measure of CO2 from as long as 15,000 years ago. Ice cores can be used for
determining CO2 levels 800,000 years ago. The trunks of trees can
also help us look back in time. As you’ve probably noticed, trees don’t just
grow up, they grow out. Every year a tree adds more wood
to its trunk, and for many trees this shows up as a tree ring. Climatologists can learn a lot about trees
from their rings because climate and weather can influence
tree growth. Scientists can use tree cores, especially
from trees that are hundreds or even a thousand years old
as a proxy for studying the Earth’s climate in times that predate
our weather records. To do this, scientists like Dr. Koutavas collect
tree cores. So you can core at will here? Tom Koutavas: We admire and respect these
organisms just like we admire and respect any part of a natural system. You’re not going to learn anything about a
natural system unless you’re able to study it. It’s like
taking a blood sample from a human being to help restore his or
her health. We learn from them in the hope that we’ll develop a better
understanding of how their ecosystem works in the broader climate
system. Flora Lichtman: Scientists like Dr. Koutavas
take these tree core data samples and combine them with other climate
records to get a clearer picture of our past climate. Tom Koutavas: This sequence of clicks eventually
will generate an 800-year -long or so record of tree ring measurements
that we can then import into our data analysis software. Compare with other samples from the same region,
normalize them, standardize them, average them, and
explore their properties in terms of their correlation with modern
climate, where they tend to overlap with instrumental records, that
allow us to interpret the nearly thousand-year-long history of this
particular sample in terms of climate variability. Flora Lichtman: In this video, we’ve talked
a lot about how climate scientists do their research. But what many
people want to know is, what does climate change mean for us? Laura Broughton: We already are seeing rises
in sea level. We’re already seeing more extreme heat days, hotter average
years than ever recorded before. Cynthia Rosenzweig: It’s not only the sea
level rise. It’s what happens when storms come along. This coastal flooding due
to that storm extends farther onto the coast, and that is the real
danger. Our flood zones, which up until now we’ve
all been organized here was our 1-in-100-year storm, and we all
knew what it was. Guess what? Our 1-in-100-year storm is not
going to be the same in the future. Flora Lichtman: In New York City, we’re going
to have a front row seat for the effects of climate change. Sea level is
already rising. We’re already seeing more extreme heat and higher
average temperatures. Models suggest that we should expect fiercer
storms, like Sandy, and more of them. City officials in New York are considering
the risks of climate change in their rebuilding plans. Cynthia Rosenzweig: This is groundbreaking
for the New York region, but not just for the New York region, but for the United
States and for the world. It’s a signal that increasing risks
due to climate change with higher sea level rise, no matter what
happens to the storms, all coastal areas are more vulnerable. Flora Lichtman: Do you get the sense that
cities are taking this seriously? Cynthia Rosenzweig: Absolutely. This is one
of our main areas of work. We work with cities all over the world. The cities
are the first responders to climate change. They are stepping up. music

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