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By Aayushi Sharma
Marine cloud brightening (MCB) is a geoengineering proposal aimed at cooling atmospheric temperatures and mitigating the impacts of climate change. However, according to a new study, cloud brightening to cool California’s climate could eventually cause heat waves to shift towards Europe.
What happens in the marine cloud brightening process?
Despite advances in mitigation efforts, the options for staying within the 1.5–2.0 °C global temperature limits outlined in the Paris Climate Agreement are becoming more limited. There are increasing discussions that achieving these targets will likely require a combination of greenhouse gas emissions reductions, carbon dioxide removal, and solar geoengineering (SG), which involves deliberate actions to cool the Earth by reflecting more sunlight into space.
Marine cloud brightening (MCB) is a solar geoengineering strategy for regional applications because it can be deployed in the lower troposphere over a relatively small area. MCB aims to cool the Earth by introducing sea salt particles into the lower atmosphere to create brighter marine stratocumulus clouds, similar to the brightening observed along the paths of large ships due to sulfate particles from ship exhaust.
While most modeling studies have examined the global climate effects of cloud brightening in idealized simulations, MCB could theoretically be used regionally to meet specific socio-political or physical goals. Reports demonstrate the potential for regional MCB to initiate a climate teleconnection, thereby reducing regional climate impacts.
Key Observations of the study:
- The 2010 simulation indicated that operating near Alaska would reduce the risk of dangerous heat exposure in the target region by 55%, equating to 22 million people-days per summer. A closer subtropical test showed smaller but still significant benefits, with a 16% reduction.
- However, in simulations of the more disrupted climate of 2050, the same operations yielded very different results due to fewer clouds, higher baseline temperatures, and a slowing of the Atlantic meridional overturning circulation (AMOC). Under these mid-century conditions, the Alaska operation would have a significantly diminished impact on reducing heat stress in the western US, while the subtropical operation would increase temperatures, contrary to the intended outcome.
What are the side effects of using MCB on the western coast of the USA?
Under current climate conditions, the research team discovered that MCB could lower the risk of extreme summer heat in parts of the western US by up to 55 percent. However, rainfall in this region and other areas worldwide, such as Africa’s Sahel, also significantly decreased.
In recent years, the Western United States has faced record-breaking summer heat waves. MCB has also been found to trigger unexpected climate responses in distant regions for the years 2010 and 2050. Under 2010 conditions, MCB strategies led to significant reductions in heat stress over land and notable precipitation changes, including decreased rainfall in the Sahel and the Western United States. However, under 2050 conditions, certain areas like northeast Asia, Europe, and central North America experience increased heat stress and hotter summers with MCB compared to what would occur under global warming alone.
Europe, in particular, faces warmer summers under both MCB strategies, despite seeing reductions in heat stress and air temperature similar to those in the Western United States in 2010. These significant remote increases in atmospheric pressure do not occur under current conditions but develop with mid-century warming, indicating that MCB induces a non-linear response within the climate system. The consistent changes in spatial response patterns under both present-day and mid-century conditions for both MCB regions suggest that the regional effectiveness of MCB is robust against CESM low cloud biases.
References:
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Image: Photo by Pixabay https://www.pexels.com/photo/grey-white-clouds-158163/
