Rising greenhouse gas concentrations cooled the atmosphere in Antarctica

In the era of global warming caused by the increase in the content of greenhouse gases in the atmosphere, adverse events may occur when there is a cooling or anti-greenhouse effect. For example, it was observed in Antarctica. This means that the situation with the regional consequences of global warming may be less clear than expected, and what increases temperature in one place may decrease temperature elsewhere.

Greenhouse gases such as carbon dioxide (CO2) and methane (CH4), transmits solar radiation that reaches the Earth’s surface, but retains the infrared (thermal) emitted by our planet. As a result, the temperature rises and the surface becomes hot; greenhouse effect occurs.

However, in some cases, these gases have the opposite cooling effect of a “greenhouse” as the atmosphere begins to transmit less of the sun’s rays, reducing the amount of energy the planet’s surface receives. This is typical, for example, of the upper atmosphere of Titan or Earth immediately after major volcanic eruptions. The magnitude of the anti-greenhouse effect depends on the presence of aerosol layers located at different heights and particles consisting of different microphysical and optical properties.

Carbon dioxide and methane enter the atmosphere for various reasons, but in recent years mainly due to human activities, namely the burning of fossil fuels. Over the past decades, greenhouse gas emissions have only increased. This led to strong warming, for example, in the Arctic. There this happens three to four times faster than the world average. As a result, the area and thickness of sea ice in the Arctic Ocean basin is rapidly decreasing.

At the same time, warming in Antarctica is not that pronounced. The ice cover of the Southern Ocean, represented mostly by seasonal ice formed during the cold period near the coast of Antarctica, remains relatively constant.

Scientists have long wondered why the Arctic is melting faster than Antarctica (which includes Antarctica and its adjacent islands and parts of the Atlantic, Indian, and Pacific oceans). There are several answers to this, but for now they are hypotheses.

According to some experts, this is because meltwater from Antarctica stabilizes the water column and ice, protecting cold surface waters from warmer deep waters. Others believe that the westerly winds blowing around Antarctica have intensified due to climate change and the “stretching” of the ice over a large area. There is another view: according to him, it is a matter of ocean circulation, in which excess heat received from the atmosphere is “removed” from Antarctica, transferred north to the equator.

A group of scientists from the University of Bremen (Germany) offered another explanation: the “anti-greenhouse effect”. The results of the study were published in the journal Geophysical Research Letters.

About a decade ago, climate scientist Justus Notholt (Justus Notholt) and colleagues first discovered the anti-greenhouse effect in the highlands of Antarctica, where the air is particularly cold and dry. This cooling phenomenon was observed in the atmosphere (at low altitude) during several months of the year when the carbon dioxide concentration increased.

At the time, climatologists suggested that the anti-greenhouse effect might partly explain why temperatures in Antarctica did not rise as quickly as in the humid Arctic, where this effect was apparently rare.

In the new study, Notholt’s team sought to understand how water vapor in the atmosphere over Antarctica and the Arctic affects the warming and cooling associated with increases in the concentration of methane and carbon dioxide in different layers of the atmosphere.

The scientists performed two computer simulations. In the first, the amount of water vapor in Antarctica’s air corresponded to levels observed in the Arctic. They found that carbon dioxide and methane had the same effect on the temperature in Antarctica as the temperature in the Arctic, that is, it increased.

The second model estimated current water vapor levels in the atmosphere over these two regions. Climatologists have modeled seasonal temperature changes according to two scenarios: the actual level and doubling of carbon dioxide and methane concentrations. It turns out that the increase in the concentration of these greenhouse gases in the Antarctic atmosphere leads to cooling of almost the entire troposphere (altitude 10-18 kilometers) and warming in the Arctic troposphere.

Yes, at twice the concentration CO2 And CH4 There was a warming of 0.42 Kelvin in the Arctic troposphere and a slight cooling of 0.01 Kelvin in the Antarctic troposphere.

At altitudes up to seven thousand meters above the surface with twice the concentration CO2 The average temperature increased by 0.81 Kelvin in the Arctic and by 0.16 Kelvin in Antarctica. But the same amount CH4 A cooling of 0.06 kelvin was observed in Antarctica and a warming of 0.07 kelvin was observed in the North Pole.

Like greenhouse gases, water vapor also affects the greenhouse effect. The amount of water vapor in the air depends on temperature; The higher the temperature, the more moisture it can contain. In other words, Antarctica’s colder, drier atmosphere responds differently to increased greenhouse gas emissions than the Arctic’s moist, warmer atmosphere.

“As humidity increases with temperature and Antarctica gets warmer each year, the anti-greenhouse effect may eventually turn into a greenhouse effect,” Notholt said.

The authors are confident that the results of their research will help explain why Antarctica has seen a less pronounced warming effect over the decades compared to the Arctic.