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The Antarctic Paradox · The Climate Translation

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One of the things I enjoy most about science is that sometimes the most important discoveries
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begin with something that doesn't make sense.
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Imagine you have a huge jigsaw puzzle, and every piece is falling into place.
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Except for one, and no matter how many times you look at it, it refuses to fit.
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For decades, climate scientists had a puzzle just like that.
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As greenhouse gases increased, and much of the world's oceans steadily warmed, there
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was one region that seemed to be telling a different story, the southern ocean surrounding
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Antarctica.
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For years, it warmed much more slowly than scientists expected.
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In some places, it even showed periods of cooling.
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So what was different about Antarctica?
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A new study may finally provide an answer, and ironically, it may have not even been
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the ocean at all.
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Today we're exploring the Antarctic Paradox.
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Welcome back to the podcast.
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I'm Dr. Mac, and this is the Climate Translation.
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I want to start with a question.
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How many of you remember hearing about the ozone hole growing up?
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As someone who grew up in the 70s and 80s, it was everywhere.
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On the evening news, newspapers, and science class, there were even public service announcements
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about protecting the ozone layer, and governments around the world began phasing out chemicals
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called chlorofloralcarbons, or CFCs.
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For many of us, the ozone hole became a defining environmental story.
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These were not chemicals invented, though, with the intention of harming the atmosphere.
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When they were introduced, they seemed ideal.
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They were stable.
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They weren't toxic under normal conditions, and they weren't flammable.
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That made them great for dangerous chemicals that were previously used in refrigerators,
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and air conditioners.
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Over time, CFCs appeared everywhere.
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They were put into aerosol cans.
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They were used to create foam insulation and packaging.
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Some were even used as solvents for cleaning electronic equipment.
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Their stability was one of the qualities that made them valuable, but it was also a source
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of their problem.
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Because CFCs don't break down easily at the surface, they remain in our air, and they
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actually slowly travel up into the stratosphere.
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Once there, intense ultraviolet radiation from the sun can break the molecules apart,
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and release chlorine.
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That chlorine could then participate in additional reactions that destroyed natural ozone.
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And it wasn't just finished after destroying just one ozone molecule.
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A single chlorine atom could continue destroying ozone again and again.
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So a chemical released from a refrigerator, or an air conditioner, or an aerosol can
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at the ground, could eventually affect the atmosphere miles above us.
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And that delay also made the danger harder to recognize.
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Ironically, this environmental issue became a major public concern around the same time
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scientists began to warn us about global warming.
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And because the two of them became linked together in people's minds, it caused a problem.
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In fact, a survey conducted by researchers at Yale University found that 61% of Americans
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believed that the ozone hole was the cause of global warming.
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And 43% thought that repairing the ozone layer would slow climate change.
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It's a completely understandable conclusion to reach, after all, both involve human activities
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changing the atmosphere, and both became scientific concerns at around the same time.
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To make things even more confusing, some of the chemicals that damaged the ozone layer
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are also powerful greenhouse gases.
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So it's easy to assume they're simply part of the same problem.
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But of course, they're not.
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They're two distinct environmental challenges that just happen to interact in some fascinating
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ways.
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The ozone layer sits high above us in the stratosphere.
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That's about 10 to 30 miles above the Earth's surface.
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I like to think of ozone kind of like the Earth's sunscreen.
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It absorbs much of the sun's harmful UV radiation before it reaches the ground.
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This protects living things from levels of UV light that would otherwise be dangerous.
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We're not just talking about sunburns here, we're talking about cancer or worse.
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Global warming works very differently.
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Instead of UV, it involves infrared energy.
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The heat that the Earth is constantly trying to radiate back into space.
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Greenhouse gases like carbon dioxide and methane absorb some of the heat that's outgoing
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and re-radiated back down, making the lower atmosphere warmer.
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So while the ozone layer is like a sunscreen, greenhouse gases are like an extra blanket.
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They both influence the planet, but they do so in different physical ways.
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And that's what makes today's story so fascinating, because even though there's separate
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environmental problems, they unexpectedly influence each other.
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And the first sign of that influence appeared high above Antarctica, where the loss of
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ozone caused the stratosphere to become cooler.
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Now you heard me right, in an age of global warming, we've actually seen the stratosphere
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become colder over the southern part of our planet, as ozone was depleted.
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To understand why, we need to remember what ozone actually does.
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ozone absorbs UV radiation from the sun, and when it absorbs that energy, it warms
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the surrounding air.
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So when large amounts of ozone were lost over Antarctica, less UV energy was absorbed
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to the stratosphere, and with less being absorbed, that part of the atmosphere cooled.
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Now at first glance, that might not seem like a big deal.
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After all, we're talking about air at 10 to 30 miles above the Earth's surface.
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How could something happening that high up possibly influence the surface below?
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The answer comes down to one of the most fundamental principles of meteorology.
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The atmosphere responds to differences in temperature.
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When air becomes colder, it becomes dense and contracts.
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When air becomes warm, it becomes less dense and expands.
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Across large distances, those temperature differences affect pressure patterns at different
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heights in the atmosphere.
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Differences and pressure help create wind, and when the temperature contrast becomes extreme,
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winds become stronger as well.
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In this case, the unusually cold stratosphere over Antarctica increased the temperature contrast
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with other regions in the southern hemisphere, places like South America, Africa, Australia,
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and their surrounding oceans.
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As that contrast increased, the powerful west-to-east winds that circulate around Antarctica
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strengthened and shifted farther towards the pole.
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meteorologists call this ring of winds the polar vortex, and you've probably heard
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the phrase before in winter weather forecasts.
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In the northern hemisphere, we also have a polar vortex, and it can weaken or become distorted.
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That can release cold, Arctic air south into North America, Europe, and Asia, and supply
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the conditions that can make severe winter outbreaks possible.
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But in the southern hemisphere, it's a little different.
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Because Antarctica surrounded almost entirely by flat ocean with few mountain ranges and continents
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to disrupt the circulation, the polar vortex is generally more stable and nearly circles
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the continent like a giant atmospheric racetrack racing around and round without stopping.
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So as the stratosphere cooled, those winds became stronger and stronger, and then shifted
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closer to Antarctica.
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And that's where the atmosphere began talking to the ocean below.
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The stronger winds changed how the surface water moved around the continent.
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That influenced were cold water spread, where deeper water rose to the surface, and how heat
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was exchanged between the ocean and the atmosphere.
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In effect, it masked the effects of global warming that scientists were expecting to see
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at the surface.
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The greenhouse effect did not disappear.
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It was still adding energy to the climate system.
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But in this particular region, another human-caused influence was changing the winds and redistributing
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ocean heat at the same time.
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And so for many years, while much of the global ocean warmed, parts of the southern ocean
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warmed more slowly, and at times even cooled, it baffled scientists for a long time.
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Surely greenhouse gases had not stopped working there.
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Something else had to be altering how the region responded.
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It was a paradox.
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But over time, better satellite observations, ocean measurements, and climate models allowed
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researchers to build a clear picture of what was happening.
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And once scientists began to suspect the connection, they had to answer a question.
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How could they prove it?
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So scientists had a hypothesis.
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They suspected that the ozone hole had strengthened the winds around Antarctica, and those stronger
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winds had changed how the southern ocean moved heat.
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But suspicion isn't proof.
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In science, you have to test your ideas.
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So how do you test something?
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You can't recreate an laboratory.
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Well you build a computer model.
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Imagine you build two identical worlds in a simulator.
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You give them the same land forms, the same atmosphere, the same ocean currents, the same
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amount of sunshine.
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The only difference is, in World A, you turn off its ozone layer.
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And in World B, you leave the ozone perfectly healthy.
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Then you observe the weather patterns.
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Do they drift apart?
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If so, you've learned something about exactly what ozone does.
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Climate scientists did something similar, but with a lot more complex calculations.
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They began with models that included a lot of other things in the Earth's climate,
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greenhouse gases, volcanoes, wind currents, changes in the sun's energy, seasons, ocean
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circulation, and among others, yes, the ozone layer.
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Then they changed only one variable.
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In this case, they ran simulations that included a loss of ozone over Antarctica.
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And they ran many simulations, comparing each other, where the ozone layer remained
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unchanged, and where it was in various stages of loss.
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Everything else remained the same.
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And the models began to show that ozone depletion produced stronger winds around Antarctica
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and a cooler southern ocean, while the other models did not.
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It was powerful evidence that ozone loss was playing an important role.
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But scientists didn't stop there.
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A computer simulation, by itself, is not enough.
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You have to match what's actually being observed, so researchers compared their simulations
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with decades of measurements from satellites, weather balloons, ships, ocean buoys, and other
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observations collected around Antarctica.
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The pieces came together.
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Everything matched.
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The wind changes matched.
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The pattern of cooling of the southern ocean matched.
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The paradox seemed to have been solved.
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We didn't get there through a one big aha moment, though.
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That's not how science works.
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Instead, it was about stacking up dozens of independent clues into a conclusion became
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impossible to ignore.
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It cleared up a mystery that had stumped climate scientists for decades.
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But solving one puzzle often hands you a new one.
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If the ozone hole was acting as a temporary shield against the heat, what happens now that
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the ozone layer is healing.
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The story of our ozone hole begins with one of the greatest environmental success stories
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in modern history.
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Once scientists discovered that CFCs were damaging the ozone layer.
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Countries around the world did something remarkable.
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In 1987, they adopted the Montreal Protocol.
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Nations that disagreed on other issues came together with a common goal to phase out chemicals
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destroying the ozone layer.
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And it worked.
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Measurements collected over the past several decades show that the ozone layer is gradually recovering.
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The Antarctic ozone hole still forms each spring, but scientists are continuing to expect
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it to shrink over the coming decades as the atmosphere slowly removes the remaining
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CFCs.
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That's worth celebrating.
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It demonstrates something important about science.
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Scientists identified a problem, they uncovered a cause, and the world responded.
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The atmosphere began to heal.
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That's exactly how we hope science and society work together.
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But here's where the story takes a twist.
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Remember that the cooling of the southern ocean wasn't caused by the ozone hole directly.
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It was caused by changes in atmosphere circulation that the ozone hole created.
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As the ozone layer recovers, those changes are going to weaken.
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The exceptionally strong winds around Antarctica are expected to gradually relax toward a
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more typical state, and as they do, their cooling influence on the southern ocean will fade.
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That means global warming becomes more evident.
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It won't happen overnight, but scientists are expecting the southern ocean to increasingly
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resemble the warming trends already observed across the rest of the world's oceans.
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And that raises some important questions about what comes next.
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Let's start with ice.
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Sea ice floating around Antarctica doesn't raise sea level when it melts.
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Just like melting ice cubes in a glass of water don't cause it to overflow.
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But its loss still matters.
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Seas reflects sunlight, and it insulates the ocean from the atmosphere.
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It provides a habitat for Antarctic ecosystems, and it creates a cold, salty water region that
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can sink into the deep ocean.
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The warmer ocean can make it harder for the ice to form and easier for it to melt.
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The larger concern for sea level is the ice on land.
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Much of Antarctica's land ice reaches the ocean through enormous glaciers, in many places
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those glaciers flow into ice shelves extending outward from the continent.
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Those shelves act like braces.
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They don't stop the ice behind them from moving, but they slow its journey.
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If a warmer ocean melts those braces, the glaciers can then move into the sea faster.
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And ice from the land can add to global sea level.
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Near the continent, extremely cold and salty water sinks to the ocean floor.
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This bottom water spreads across the Atlantic and Pacific, and Indian oceans, and helps
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ventilate some of the deepest part of the global ocean.
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But melting land ice adds fresh water.
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Fresh water is less dense, so it doesn't sink as rapidly.
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That means greater melting could weaken the production of deep water, altering the slow
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overturning circulation that moves oxygen, carbon, and nutrients throughout our oceans.
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Then there's the atmosphere.
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The winds surrounding Antarctica help influence storm tracks and rainfall across the southern
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hemisphere.
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When those winds strengthen, weaken, or shift north and south, the effects can reach
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parts of Australia, southern Africa, South America, and the surrounding oceans.
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That does not mean ozone recovery alone will determine the weather in those places.
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Greenhouse gases, ocean temperatures, tropic variability, and year-to-year changes will
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continue to play a role.
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But if the circulation around Antarctica changes, the pathways followed by storms and moisture
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may change.
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Over the next century or two, Antarctica will not simply respond to one influence.
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Ozone recovery will be occurring while greenhouse gases continue to warm the atmosphere and
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the ocean.
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Sea ice will interact with changing winds.
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Melting land ice will add fresh water to our oceans, and those changes may feed back
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into changes in ocean circulation and the atmosphere above it.
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We cannot describe every detail of that future with certainty.
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How much changes or how quickly will depend heavily on how much warming occurs.
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But the Antarctica our descendants' experience, one or two centuries from now, could operate
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very differently from the Antarctica scientists began observing during the 20th century.
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The paradox helped hide some of that change for a time.
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But as it fades, we may begin to see more clearly just how sensitive the southern edge of
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our planet really is.
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Antarctica once appeared to be resisting part of the warming seen around the rest of our
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planet.
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Now, we understand that the ozone hole wasn't stopping climate change, but it was temporarily
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changing the winds and ocean circulations around the continent.
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As the ozone layer heals, that influence will fade, revealing a southern ocean entering
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a very different future.
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The Antarctic paradox was never that global warming had failed.
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It was another human cause change that had briefly hidden parts of the signal.
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I'm Dr. Mac, and this has been the Climate Translation.
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If you have a question about the climate that you've been too afraid to ask, or if you
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have a different opinion, I want to hear from you.
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I can use your viewpoints in future episodes.
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You can reach me at theclimatetranslation at gmail.com.
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I'll see you next time.