Climate engineering off US coast could increase heat waves in Europe, study finds

A geoengineering technique designed to reduce high temperatures in California may inadvertently intensify heat waves in Europe, according to a study that models the unintended consequences of shifting the region to a changing climate.

The paper shows that targeted interventions to reduce temperature in one area for one season may bring temporary benefits to some populations, but this must be weighed against potentially negative side effects in other parts of the world and rates of change in effectiveness over time. times.

The study’s authors said the findings were “alarming” because the world has little or no regulation to prevent regional applications of the technique, marine cloud lighting, which involves spraying reflective aerosols (usually in the form of sea salt or sea spray). in stratocumulus clouds over the ocean to reflect more solar radiation back into space.

Experts have said that the lack of controls means there is little to prevent individual countries, cities, companies or even wealthy individuals from trying to modify their local climate, 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 organizations to engage in geoengineering research that was once virtually taboo.

In Australia, scientists have been experimenting with marine cloud brightening strategies for at least four years in an attempt to cool the Great Barrier Reef and slow its bleaching.

Earlier this year, scientists at the University of Washington sprinkled sea salt particles across the flight deck of a decommissioned aircraft carrier, the USS Hornet, docked at Alameda in San Francisco Bay. This experiment was halted by the local government to allow it to assess whether the spray contained chemicals that could pose a health risk to humans or animals in the Bay Area.

The new paper suggests that the consequences could be much larger and harder to predict. Published Friday in Nature Climate Change, the authors claim to be the first to demonstrate that cloud brightening effects may be reduced or reversed 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 conducted over different regions of the northeast Pacific Ocean, one in the subtropics near California and one in the midlatitudes near Alaska. . Both are designed to reduce the risk of extreme heat in the target region, the US West Coast.

Counterintuitively, the more distant operation had greater impact because it used “telecommunications links,” links in the climate system between geographically distant parts of the world.

The 2010 simulation suggested that the operation near Alaska would reduce the risk of dangerous heat exposure in the target region by 55%—equivalent to 22 million person-days in summer—while the closer subtropical test would produce smaller gains. , but still significant of 16%. .

However, in the more intermittent 2050 climate simulations, the same two runs produced very different results because there were fewer clouds, higher core temperatures and different ocean current patterns, most importantly a slowing of the overturning circulation meridional Atlantic (Amoc). Under these mid-century conditions, operation near Alaska would have a drastically reduced effect on alleviating heat stress in the western US, while subtropical operation would increase temperatures—the opposite of the desired result.

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Consequences outside the target regions were also significantly different between 2010 and 2050. At the earlier date, simulations suggested that Europe would also be cooled by marine clouds shining in the North Pacific. However, by 2050, local cooling will increase heat stress worldwide, especially in 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 the Scripps Institution of Oceanography at UC San Diego. “This shows that marine cloud brightening can be very effective for the west coast of the US if done now, but will be ineffective there in the future and cause heat waves in Europe.”

She said the results should concern policymakers and prompt them to create governance structures and transparency guidelines, not only at the global level, but also regionally.

“There’s really no governance of solar geoengineering right now. This is scary. Science and politics must develop together, otherwise we will be disappointed,” she said. “We don’t want to be in a situation where one region is forced to do geoengineering to combat what the rest of the world has done to respond to drought and heat waves.”

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