It may sound counterintuitive, but
new research suggests that cleaning up air pollution could contribute to a
weakening of the Atlantic Meridional Overturning Circulation (AMOC). This is
the ocean current system that acts like a giant conveyor belt, moving warm
surface water northward and cool deep water southward.
Increasing concentrations of greenhouse gases such as carbon dioxide and methane are already
known to weaken the AMOC. But according to a study published in the journal Environmental Research:
Climate, that weakening could be accelerated by reducing air pollution,
specifically pollutants such as sulfur dioxide and black carbon, that float over Europe and
North America.
An international team of
researchers used eight different climate models to see how changes in
human-made air pollution affected the strength of the AMOC. They ran a total of
80 simulations and looked at what happens across the globe and within specific regions
between the years 2015 and 2050 under two key scenarios—one with strong air
pollution controls and the other with weak controls.
Cleaner air could be a problem
The team found that cleaning up air
pollution globally will cause the AMOC to weaken by about 6% by the middle of
the century. This reduction is on top of the weakening already caused by
greenhouse gases. However, this effect varied by location.
The impact on the AMOC was greatest
when pollution was reduced in North America and Europe, followed by Africa, the Middle East,
and East Asia. In South Asia, reducing emissions has a minimal statistical
effect on the current. As the researchers note in the study, "Efforts to
improve air quality, particularly around the Atlantic basin but also far away
in East Asia, will contribute to future AMOC weakening."
So, what is happening?
According to the paper, aerosols
act like a temporary sunshade that reduces how much sunlight reaches the ocean.
When this pollution is cleaned up, the extra sunlight warms the North Atlantic,
disrupting the temperature balance needed to keep the conveyor belt moving.
"Aerosol perturbations that feature larger positive North Atlantic ERF
are associated with larger AMOC weakening," continued the scientists.
The research has highlighted a
catch-22 situation. On the one hand, we need to remove air pollution to protect
human health and save lives. Yet if we do, we risk worsening the effects of
climate change.
Ultimately, these findings present policymakers with a monumental challenge. Namely, finding ways to clean up the air we breathe without influencing major ocean circulation systems in unintended ways.
Source: Climate catch-22: Cleaning up air pollution could speed key Atlantic current decline
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