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By Daisy Dunne
Sprayed aerosols in the stratosphere could curb global warming, but would not prevent the oceans from warming up, according to a new study.
The results suggest that this type of "solar geoengineering" "A set of techniques to combat global warming by reflecting sunlight in space" may not necessarily stem the rise of the level of the sea or prevent damage to the world's marine ecosystems.
Research indicates solar geoengineering could have "major" effects The lead author told Carbon Brief.
The study also raises the question of whether global average temperature is "the best measure to take into account" to combat the effects of climate change, another scientist told Carbon Brief. [19659006] Exploiting a Volcano
Scientists have suggested that releasing aerosols into the atmosphere, a technique called "aerosol injection into the stratosphere" – could cool the planet in the same way volcanic eruption.
When a volcano declares itself, it sends a cloud of ash high into the atmosphere. Sulfur dioxide released into the plume combines with water to form sulfuric acid aerosols, which reflect incident solar light, temporarily cooling the Earth.
The artificial introduction of aerosols into the atmosphere, via a plane or balloon at high altitude, could have According to researchers, this cooling effect is similar. The idea has never been tested, but previous research using computer simulations suggests that releasing aerosols could help limit the rise in global temperature to 1.5 ° C – l & # 39; 39 ambitious goal of the Paris Agreement – and to prevent precipitation However, an aerosol sun visor would not protect the planet from increasing CO2 emissions – making oceans more acidic and crops less nutritious, among other problems.
The new study published in Nature Geoscience. , identifies, for the first time, another potential loss of the proposed technique: it may not be able to limit warming in the depths of the ocean.
This is because aerosol releases could lead to decreased precipitation in some areas, which could affect ocean circulation patterns, says lead author Dr. John Fasullo, a researcher with project at the Boulder National Atmospheric Research Center (NCAR). He explained to Carbon Brief:
"The explanation has two key steps: in the first, aerosols reduce the amount of precipitation that occurs in the world.This change is not uniform, but the Reductions are greater in some key regions, namely, the North Atlantic Ocean – and this increases the salinity of these ocean areas, making the water more dense. "
This increase in water density could speed up the "southern overturning traffic of the Atlantic" (AMOC), he said. AMOC is a perpetual conveyor belt that transports heat from the equator to the North Atlantic. It is part of a larger network of global ocean circulation patterns that carry heat around the world. Fasullo said:
"The North Atlantic is a key part of deep-water formation, and higher density means that it is accelerated, and deep-sea formation speeds deeper into the depths. of the ocean that would otherwise have "
Other Worlds
To explore the impact of aerosol releases on the oceans, researchers used a series of 20 computer simulations to determine what would happen if the aerosols were rejected between 2020 and 2099. This set of simulations is known as "large geoengineering ensemble" (GLENS).
The simulations badume that aerosols are released at uniform points around the world. (Previous research has shown that this would prevent large regional changes in temperature and time.)
Researchers compared their geoengineering simulations to another set of simulations in which no geoengineering took place and where little measures were being taken to combat climate change and generate high emissions. in the coming decades (a scenario known as "RCP8.5").
The graph below shows how the global mean temperature (solid lines, y-axis on the left) and the global rainfall levels (dashed lines on the right) on the y-axis should differ between the simulations of the scenario of High emissions (RCP8.5) and GLENS.
Above: Modifications of global mean temperature (solid lines, y-axis on the left) and global precipitation (dashed lines, y-axis on the right) in a scenario with solar geoengineering (GLENS, in blue) and a scenario without geoengineering and high greenhouse gas emissions (RCP8.5, in red). Source: Fasullo et al. (2018)
The graph shows how, in the world of geoengineering, global average temperature is kept constant as precipitation levels decrease. In comparison, the temperature and precipitation levels continue to increase in the high emissions scenario.
The maps below show the expected changes in the heat content of the ocean between 2010-30 and 2075-95 in the upper part. ocean (0 to 300 m, left) and across the depth of the ocean (right) in the geoengineering scenario. On the cards, the red color indicates an increase in the COH, while the blue color decreases.
Above: Planned changes in the heat content of the ocean between 2010-30 and 2075-95 in the upper ocean (0 to 300 m; left) and in total depth from the ocean (right) as part of a solar geoengineering scenario. Red indicates an increase in OCH, while blue indicates a decrease. Source: Fasullo et al. (2018)
The graphs show how, in the geoengineering scenario, shallower areas of the ocean should warm up. This includes the Arctic Sea and the waters off the west coast of North America.
However, in the depths of the ocean, many other areas are expected to experience an increase in CMO, with probably greater warming. in the Arctic Sea and in the Southern Ocean.
Rising Tides
The findings suggest that, contrary to previous research, solar geo-engineering might not prevent sea-level rise.
The rise in the level of the sea is mainly due to the expansion of seawater following the warming and melting of land ice at the poles of the world. In some areas, including in West Antarctica, melting occurs when land ice comes in contact with the warm waters of the ocean. Fasullo said:
"Compared to today, it is extremely likely that sea level will continue to rise under our geoengineering approach, but it is also likely that the rate of this increase will be lower than that of 'an ordinary business'. climatic trajectory [RCP8.5].
"We can not say with certainty what this rate of increase could be because we do not have models of ice sheets fully coupled to our climate simulations, and we have not sufficiently controlled
The results could also mean that solar geo-engineering could not prevent marine heat waves, which pose a major threat to underwater wildlife, and the expected increase in the intensity of hurricanes. (Although no research has examined It is still too early to draw conclusions, said Fasullo.)
The study raises the question of knowing whether global average temperature "is the best measure to take into account" to cope with the impacts of climate change e, said Professor Govindasamy Bala, a physics scientist at the Institute's Divecha Center for Climate Change Indian Science, who did not participate in the study. He told Carbon Brief:
"However, as there is only one modeling study, it's hard to know if the results of this article are robust. based on several models would be needed to verify its robustness. " [19659002] The results suggest that solar geo-engineering could have "significant drawbacks," Fasullo said:
"Several senior decision-makers in the United States have described climate change as a technological challenge. our job is that geo-engineering itself has major uncertainties and risks. "
Reposted with the permission of our press attaché Carbon Brief.
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