How air pollution is heating up Southern Ocean

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Researchers have identified a lesser-known form of ozone playing a big role in heating the Southern Ocean — one of Earth’s main cooling systems.

Ozone is a gas composed of three oxygen atoms. Many studies have described ozone in the stratosphere, and its role in shielding people from the sun’s harmful ultraviolet radiation. Closer to ground level, in the troposphere, ozone is harmful to humans.

In the study led by University of California-Riverside scientists revealed that lower level ozone is adding a great deal of heat to the Southern Ocean — more than scientists previously understood.

“People haven’t paid much attention in the past to tropospheric ozone in terms of ocean heat uptake. Based on our models, they should be,” said lead author Wei Liu, climate scientist at the varsity. The finding has been published in the journal Nature Climate Change.

Oceans remove a majority of the carbon and heat that enter the atmosphere when humans burn fossil fuels.

The Southern Ocean, also called the Antarctic Ocean, collects a third of all excess carbon in the world’s atmosphere, and an estimated 75 per cent of the excess heat collected by the world’s oceans.

It is important to understand this heating so it can be controlled. Increased ocean warming is contributing to well-documented issues of sea levels rising.

To further this understanding, Liu and an international team of scientists explored climate model simulations with changes in ozone levels between 1955 and 2000.

These model simulations isolated both stratospheric and tropospheric ozone from other influences on Southern Ocean temperatures, allowing them to see how each factor contributes.

While both stratospheric and tropospheric ozone contribute to the Southern Ocean warming, the team found that the latter contributes more.

“Historically, about a third of the ocean’s warming is attributable to ozone. For this third, about 40 per cent is from the stratosphere, and the rest is troposphere,” Liu said.

Liu believes the results of this study are useful for showing where people can make further changes that will improve the environment.

Volatile organic compounds, or VOCs, from products like pesticides, tobacco smoke and automobiles are gases that form the building blocks of tropospheric ozone. The same is true for nitrogen oxides produced by combustion, or carbon monoxide from furnaces, gas stoves, and automobile exhaust. Many of these products can be modified to produce fewer VOCs.

“Tropospheric ozone is an air pollutant,” Liu said. “If we reduce our production of this, we get the dual benefits of less air pollution and most likely, less Southern Ocean warming as well.”

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