Why is the Caspian Sea Evaporating?

The largest lake in the world is gradually shrinking thanks to a changing climate, and beach towns could become landlocked.

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Episode Transcript

Speaker 1 (00:02):
Welcome to brain stuff from how stuff Works a brain stuff,
I'm Christian Sager. When the ancient Romans arrived at the
Caspian Sea a couple of thousand years ago, they thought
they'd arrived at an ocean. That's because the water they
encountered was salty. Nestled amongst modern day Russia, Kazakhstan, Turkmenistan, Azerbaijan,

(00:24):
and Iran, the Caspian Sea actually is the world's largest lake.
For comparison, Lake Superior is the world's largest freshwater lake,
with the surface area of thirty one thousand, seven hundred
square miles or eighty two thousand, one hundred square kilometers.
The Caspian Sea occupies a space significantly larger, at a

(00:48):
hundred and forty three thousand, two hundred square miles or
three hundred and seventy one thousand square kilometers for a
US reference, that's like comparing the sizes of Maryland and Montana.
The Caspian seas waters are brackish, about a third as
salty as most ocean water. Because the water finds its

(01:09):
way into it from about a hundred and thirty different
freshwater sources. It has no outlet. If water is going
to escape the Caspian Sea, it's got to do it
through evaporation. So it's strange that the water level of
the Caspian Sea has been steadily dropping for the past
couple of decades. Between nineteen six and two thousand and fifteen,

(01:30):
the sea has drawn down about three inches or seven
centimeters per year. That's about five ft or one point
five meters total. This is not the first time water
levels in the Caspian have dramatically dropped. Over the course
of the twenty century. Changes in agricultural practices in its basin,
as well as industry in damming in the Vulgar River,

(01:52):
which accounts for eighty percent of the inflow of water,
all of it pulled the seed down the three feet
or one me or below what it is today by
the late nineteen seventies. But a new study published in
Geophysical Research Letters finds that the Caspian seas current shrinking
is due to the water simply evaporating away, driven by

(02:15):
increasing average atmospheric temperatures. The researchers found that between the
two time frames they studied the years between nineteen seventy
nine and nine, and then again between nine and fifteen,
the average yearly air temperatures directly above the sea rose
by about one point eight degrees fahrenheit or one degree celsius. Now.

(02:40):
Co author Clark Wilson said, what really controls the sea
going up and down over long periods of time is
most likely evaporation, which is almost completely dominated by temperature.
This study is the first to provide convincing evidence that
the Caspian Seas water levels are changing due to evaporation

(03:01):
and a changing climate, rather than things like changes in
river discharge or rainfall. If the trend continues, evaporation will
have the biggest impact on the shallowest parts of the
sea first. Much of the water at the sea's northern tip,
for instance, is only about sixteen feet or five meters deep.
At this rate of evaporation, that portion will disappear within

(03:25):
seventy five years. Cities currently located on the shore would
quite quickly become landlocked as waters recede, and many of
these population centers derive significant economic value from the sea,
from tourism to fishing to shipping. Additionally, the Caspian Sea
is home to some pretty crazy ancient animals that would

(03:47):
be out of a home if the sea disappeared. The
Caspian was part of the Teta's Ocean about three hundred
million years ago. Relatives of some of those species remain,
including a whopping of the world's caviare producing and endangered sturgeon.

(04:12):
Today's episode was written by Jesslyn Shields, produced by Dylan Fagan,
and For more on this and other topics, please visit
us at how stup works dot com.