In the sky above you there’s a tricky chemical trade-off at work. Greenhouse gases are harming environmental wellness by warming the earth’s surface, but aerosol pollution in the atmosphere actually, in part, counteracts this damage to the wellbeing of the planet. But what exactly is aerosol pollution, and how does it work?
An aerosol is a suspension in the air of fine solid particles or liquid droplets in a gas, and can come from both natural and industrial sources, such as clouds, air pollution such as smog and smoke, sea salt, mineral dust, ash, soot, sulphates, nitrates, and black carbon. Aerosols scatter and absorb radiation from the sun, hanging around in the air for roughly 10 days. They also boost cloud formation by providing nuclei for water droplets, which decreases the amount of energy that reaches the ground and provides a net cooling force.
A greenhouse gas (GHG), on the other hand, is a gas in the atmosphere, such as water vapour, carbon dioxide, methane, nitrous oxide, and ozone that absorbs and emits radiation within the thermal infrared range. Simply put, greenhouse gases warm the surface; aerosols cool the surface, so there shouldn’t be a problem, right?
This balance of GHGs and Aerosols creates a dilemma in parts of Asia. The coal burning in China and India creates an aerosol problem far worse than the United States or Europe ever had, and kills hundreds of thousands every year. However, because of the GHG trade off, if these countries began to fix their aerosol problem without also cutting greenhouse gas emissions, they might actually contribute to global warming.
According to Marshall, the Cecil and Ida Green Professor of Oceanography, ‘It’s about quantification. One of the biggest challenges of climate science is to quantify the relative role of aerosols and oceans in cooling the planet’s surface vs. the greenhouse gases warming it. Just knowing the trade-off happens isn’t enough to make useful predictions and inform policy makers.’
However, Gavin Schmidt, climatologist and climate modeller at the NASA Goddard Institute for Space Studies (GISS), adds that, at present, ‘we simply don’t have sufficient constraints on the history, spatial distribution and microphysics of anthropogenic aerosols’ to model aerosol effects on climate variability. Therefore, it’s likely that any action taken to address the issue will have to occur without precise quantification of the effects of aerosols or GHGs on the climate.
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