Carbon dioxide has an unexpected effect in Antarctica

At the bottom of the world, carbon dioxide is doing something surprising. Rising levels of this gas normally cause warming. But over central Antarctica, they produce a cooling. That’s the finding of a new study.

This discovery does not undermine climate science, the researchers note. Rising levels of greenhouse gases, such as carbon dioxide, do raise temperatures elsewhere. The effect is instead a sign of how extreme and unique the conditions are in Antarctica.

“We’re not saying the greenhouse effect is rubbish,” says Justus Notholt. He is an atmospheric physicist at the University of Bremen in Germany. It’s just that “in Antarctica, the situation is different.”

Earth is warm enough to support life because of the greenhouse effect. Greenhouse gases prevent some of the sun’s energy from escaping back into space. But human activities, such as burning fossil fuels, have increased the amount of these gases in the atmosphere. As a result, temperatures have risen most everywhere.

Except central Antarctica.

This is the only place on Earth where surface temperatures are regularly colder than those some 8 to 50 kilometers (5 to 31 miles) above the surface. This second layer of the planet’s atmosphere is known as the stratosphere. And over central Antarctica, excess carbon dioxide actually boosts the amount of heat escaping into space. This is the opposite of what happens everywhere else.

The surprising finding will appear in Geophysical Research Letters.

Antarctica is unique

Unlike the rest of Earth, the Antarctic interior has not warmed over the last few decades. It has even shown signs of cooling slightly. A chilling effect from carbon dioxide in the atmosphere might partly explain this. More research would be needed to prove that, though, Notholt says.

Carbon dioxide absorbs and emits heat energy as infrared radiation. A form of light, it’s outside human vision. This light emerges from Earth’s relatively warm surface. When it hits a molecule of carbon dioxide in the air, the molecule can absorb the radiation’s energy. The molecule later reemits that energy as infrared light.

Like a pinball machine, the carbon dioxide molecule fires off that energy in random directions. Sometimes the energy continues out to space. Other times it returns to the surface. And when it does that, it creates what’s known as a greenhouse warming.

Where carbon dioxide blocks some of this radiation from the surface, satellites see it as a dip in the amount of energy — heat — escaping into space. So the ground level warms. But over central Antarctica, satellites see an increase in heat escaping into space.

Notholt and colleagues now call this the “negative” greenhouse effect.

And they propose that it’s due to the region’s super-frigid temps. This is the coldest place on Earth. Surface temperatures can fall to −93.2° Celsius (−136° Fahrenheit). That’s typically colder than the stratosphere.

The surface is so cold that little infrared radiation leaves. That is true even though the Antarctic Plateau is covered by ice and snow. Those surfaces reflect sunlight. But, as in other places around the world, carbon dioxide in the stratosphere over Antarctica soaks in heat. And that sends infrared radiation pinballing in different directions. That siphons some heat into space that might otherwise remain near Earth.

Elsewhere, this effect is normally overshadowed by the trapping of heat from the ground. But in Antarctica, so little heat comes from the ground that the loss becomes significant. What results is an overall cooling.

Just because part of the atmosphere cools doesn’t mean the mechanism cools the ground below too, says Scott Rutherford. He is an environmental scientist at Roger Williams University in Bristol, R.I.

The new work does predict that other places with frigid surfaces, such as Greenland, should see a reduced — but still positive — greenhouse effect. Temperatures in Greenland, however, are rising much faster than the global average, Rutherford notes. That suggests that the effect doesn’t significantly affect surface temperatures there.

Power Words

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atmosphere   The envelope of gases surrounding Earth or another planet.

carbon dioxide  A colorless, odorless gas produced by all animals when the oxygen they inhale reacts with the carbon-rich foods that they’ve eaten. Carbon dioxide also is released when organic matter (including fossil fuels like oil or gas) is burned. Carbon dioxide acts as a greenhouse gas, trapping heat in Earth’s atmosphere. Plants convert carbon dioxide into oxygen during photosynthesis, the process they use to make their own food. The abbreviation for carbon dioxide is CO_2.

climate  The weather conditions prevailing in an area in general or over a long period.

environmental science  The study of ecosystems to help identify environmental problems and possible solutions. Environmental science can bring together many fields including physics, chemistry, biology and oceanography to understand how ecosystems function and how humans can coexist with them in harmony.

fossil fuel Any fuel — such as coal, petroleum (crude oil) or natural gas —  that has developed in the Earth over millions of years from the decayed remains of bacteria, plants or animals.

greenhouse gas   A gas that contributes to the greenhouse effect by absorbing heat. Carbon dioxide is one example of a greenhouse gas.

greenhouse effect   The warming of Earth’s atmosphere due to the buildup of heat-trapping gases, such as carbon dioxide and methane. Scientists refer to these pollutants as greenhouse gases. The greenhouse effect also can occur in smaller environments. For instance, when cars are left in the sun, the incoming sunlight turns to heat, becomes trapped inside and quickly can make the indoor temperature a health risk.

infrared light A type of electromagnetic radiation invisible to the human eye. The name incorporates a Latin term and means “below red.” Infrared light has wavelengths longer than those visible to humans. Other invisible wavelengths include X rays, radio waves and microwaves. It tends to record a heat signature of an object or environment.

molecule An electrically neutral group of atoms that represents the smallest possible amount of a chemical compound. Molecules can be made of single types of atoms or of different types. For example, the oxygen in the air is made of two oxygen atoms (O₂), but water is made of two hydrogen atoms and one oxygen atom (H₂O).

physics     The scientific study of the nature and properties of matter and energy. Classical physics is an explanation of the nature and properties of matter and energy that relies on descriptions such as Newton’s laws of motion. Quantum physics, a field of study which emerged later, is a more accurate way of  explaining the motions and behavior of matter. A scientist who works in that field is known as a physicist.

radiation (in physics) One of the three major ways that energy is transferred. (The other two are conduction and convection.) In radiation, electromagnetic waves carry energy from one place to another. Unlike conduction and convection, which need material to help transfer the energy, radiation can transfer energy across empty space.       

satellite    A moon orbiting a planet or a vehicle or other manufactured object that orbits some celestial body in space.

stratosphere    The second layer of the Earth’s atmosphere, just above the troposphere, or ground layer. The stratosphere stretches from 10 kilometers to 50 kilometers (about 6.2 to 31 miles) above sea level.

sun The star at the center of Earth’s solar system. It’s an average size star about 26,000 light-years from the center of the Milky Way galaxy. Or a sunlike star.