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COOLING CALIFORNIA COULD HEAT UP EUROPE  
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Jonathan Watts
June 21, 2024
Guardian
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_ Scientists call for regulation to stop regional use of marine cloud
brightening that may cool one region in the short term but have
negative impact elsewhere _

Wildfire, by USFWS/Southeast, Public Domain Mark 1.0.

 

A geoengineering technique designed to reduce high temperatures in
California could inadvertently intensify heatwaves in Europe
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that models the unintended consequences of regional tinkering with a
changing climate.

The paper shows that targeted interventions to lower temperature in
one area for one season might bring temporary benefits to some
populations, but this has to be set against potentially negative
side-effects in other parts of the world and shifting degrees of
effectiveness over time.

The authors of the study
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findings were “scary” because the world has few or no regulations
in place to prevent regional applications of the technique, marine
cloud brightening, which involves spraying reflective aerosols
(usually in the form of sea salt or sea spray) into stratocumulus
clouds over the ocean to reflect more solar radiation back into space.

Experts have said the paucity of controls means there is little to
prevent individual countries, cities, companies or even wealthy
individuals from trying to modify their local climates, even if it is
to the detriment of people living elsewhere, potentially leading to
competition and conflict over interventions.

The recent sharp rise in global temperatures has prompted some
research institutions and private organisations to engage in
geoengineering research that used to be virtually taboo.

In Australia, scientists have been trialling marine cloud brightening
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for at least four years to try to cool the Great Barrier Reef and slow
its bleaching.

Earlier this year, scientists at the University of Washington sprayed
sea-salt particles across the flight deck of a decommissioned aircraft
carrier
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the USS Hornet, docked in Alameda in San Francisco Bay. This
experiment was halted by the local government to allow it to evaluate
whether the spray contains chemicals that might pose a health risk to
people or animals in the Bay area.

The new paper suggests the consequences could be much further reaching
and harder to predict. Published on Friday in Nature Climate Change,
the authors claim to be the first to demonstrate that cloud
brightening effects can diminish or reverse as climate conditions
change due to the already dramatic human impacts of burning fossil
fuels and forests.

Using Earth system computer models of the climate in 2010 and 2050,
they simulated the impacts of two cloud brightening operations carried
out over different regions of the north-eastern Pacific Ocean, one in
the subtropics near California and one in the mid-latitudes near
Alaska. Both were designed to reduce the risk of extreme heat on the
target region, the US west coast.

Counterintuitively, the more distant operation had the greater impact
because it tapped into “teleconnections”, links in the climate
system between geographically remote parts of the world.

The 2010 simulation suggested the operation near Alaska would lower
the risk of dangerous heat exposure in the target region by 55% –
equivalent to 22 million people-days per summer – while the closer
subtropical test would cause smaller but still significant gains of
16%.

In simulations of the more disrupted climate of 2050, however, the
same two operations produced very different results because there were
fewer clouds, higher base temperatures and a slowing of the Atlantic
meridional overturning circulation (Amoc). Under these mid-century
conditions, the operation near Alaska would have a drastically reduced
effect on relieving heat stress in the western US, while the
subtropical operation would push temperatures higher – the opposite
of the desired result.

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The consequences outside the target regions were also markedly
different between 2010 and 2050. At the earlier date, the simulations
suggested Europe would also be cooled by the marine cloud brightening
in the north Pacific. However, by 2050, the local cooling operation
would increase heat stress around the world, particularly over Europe,
as a result of the slowing of Amoc.

“Our study is very specific,” said Jessica Wan, who is part of the
research team led by UC San Diego’s Scripps Institution of
Oceanography. “It shows that marine cloud brightening can be very
effective for the US west coast if done now, but it may be ineffective
there in the future and could cause heatwaves in Europe.”

She said the results should concern policymakers, and prompt them to
establish governance structures and transparency guidelines, not just
on a global level but regionally.

“There is really no solar geoengineering governance right now. That
is scary. Science and policy need to be developed together,” she
said. “We don’t want to be in a situation where one region is
forced to do geoengineering to combat what another part of the world
has done to respond to droughts and heatwaves.”

_Jonathan Watts is the Guardian's global environment editor. Twitter
@jonathanwatts_

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