Marine cloud brightening
[1] The intention is that increasing the Earth's albedo, in combination with greenhouse gas emissions reduction, would reduce climate change and its risks to people and the environment.
Today, emissions particles mix with clouds in the atmosphere and increase the amount of sunlight they reflect, reducing warming.
[3] Changes to shipping regulations in enacted by the United Nations’ International Maritime Organization (IMO) to reduce certain aerosols are hypothesized to be leading to reduced cloud cover and increased oceanic warming, providing additional support to the potential effectiveness of marine cloud brightening at modifying ocean temperature.
In fact, the latest IPCC report considers aerosol-cloud interactions as one of the current major challenges in climate modeling in general.
This would counteract the warming caused by a doubling of the preindustrial atmospheric carbon dioxide concentration, or an estimated 3 degrees Celsius,[5] although models have indicated less capacity.
[13] A 2020 study found a substantial increase in cloud reflectivity from shipping in southeast Atlantic basin, suggesting that a regional-scale test of MCB in stratocumulus‐dominated regions could be successful.
[1] Again unlike stratospheric aerosol injection, marine cloud brightening might be able to be used regionally, albeit in a limited manner.
A typical finding among simulation studies was a persistent cooling of the Pacific, similar to the “La Niña” phenomenon, and, despite the localized nature of the albedo change, an increase in polar sea ice.
For example, a potential Marine Cloud Brightening aimed at cooling Western United States could risk causing increasing heat in Europe, due to climate teleconnections such as unintended perturbation of the Atlantic meridional overturning circulation.
Its proposed program includes modeling, field experiments, technology development and policy research to study cloud-aerosol effects and marine cloud brightening.
Its co-principals are Robert Wood, Thomas Ackerman, Philip Rasch, Sean Garner (PARC), and Kelly Wanser (Silver Lining).
[29] A 2020 study found a substantial increase in cloud reflectivity from shipping in southeast Atlantic basin, suggesting that a regional-scale test of MCB in stratocumulus‐dominated regions could be successful.
This requires technology that can generate optimally-sized (~100 nm) sea-salt particles and deliver them at sufficient force and scale to penetrate low-lying marine clouds.
[5][31] The vessels would spray sea water droplets at a rate of approximately 50 cubic meters per second over a large portion of Earth's ocean surface.
Other methods were proposed and discounted, including: The costs of marine cloud brightening remain largely unknown.
[5] A report of the US National Academies suggested roughly five billion US dollars annually for a large deployment program (reducing radiative forcing by 5 W/m2).
[37][38] The UNCLOS could thus be interpreted as obligating the involved Parties to use methods such as marine cloud brightening if these were found to be effective and environmentally benign.
Compared with other proposed solar radiation management methods, such as stratospheric aerosols injection, marine cloud brightening may be able to be partially localized in its effects.
Potential disadvantages include that specific MCB implementations could have a varying effect across time; the same intervention might even become a net contributor to global warming some years after being first launched, though this could be avoided with careful planning.
