Cloud Engineering to mitigate global warming

A study published in Nature Geoscience reveals that marine cloud brightening (MCB), or marine cloud engineering, primarily functions by augmenting cloud cover, contributing to 60-90% of the cooling impact, as discovered by researchers from the University of Birmingham.

Prior models employed for estimating the cooling impacts of Marine Cloud Brightening (MCB) have primarily concentrated on the capacity of aerosol injection to induce a brightening effect on the cloud, thereby augmenting the quantity of sunlight that is reflected back into space.

MCB, or Marine Cloud Brightening, has garnered significant interest in recent years as a means of mitigating the adverse impacts of human-induced global warming and providing a temporary respite while the global economy transitions to a low-carbon state.

The process involves the release of minuscule particles, known as aerosols, into the atmosphere. These particles interact with clouds and are primarily intended to enhance the clouds' ability to reflect sunlight.

Currently, experiments employing this technique are already being implemented in Australia with the aim of mitigating bleaching on the Great Barrier Reef.

Nevertheless, the mechanisms by which MCB induces a cooling effect and the manner in which clouds react to aerosols remain inadequately comprehended due to the presence of variable factors, such as the interference caused by co-varying meteorological conditions.

In order to examine the phenomenon, the scientists conducted a 'natural experiment' by utilizing aerosol injection resulting from the effusive eruption of Kilauea volcano in Hawaii. This experiment aimed to analyze the connections between these naturally occurring aerosols, clouds, and climate.

The team utilized machine learning algorithms along with historical satellite and meteorological data to develop a predictive model that demonstrates the behavior of clouds during periods of volcanic inactivity.

This predictor allowed them to accurately discern the effects on the clouds that were directly attributable to the volcanic aerosols.

They demonstrated that cloud cover experienced a relative increase of up to 50% during volcanic activity periods, resulting in a regional cooling effect of up to -10 W m-2.

The measurement of global heating and cooling is expressed in watts per square meter, where a negative value indicates cooling.

It is important to understand that if the amount of CO2 in the atmosphere is doubled, it would result in an increase in global average temperature by approximately +3.7 W m-2.

The research was conducted in partnership with the Met Office, the Universities of Edinburgh, Reading, and Leeds, ETH Zurich in Switzerland, and the University of Maryland and NASA in the USA.

Lead author, Dr Ying Chen, of the University of Birmingham, said: "Our findings show that marine cloud brightening could be more effective as a climate intervention than climate models have suggested previously. Of course, while it could be useful, MCB does not address the underlying causes of global warming from greenhouse gases produced by human activity. Therefore, it is important to consider it as a 'painkiller' rather than a complete solution. We should focus on enhancing our fundamental knowledge of how aerosols affect clouds, conducting more research on the global effects and risks of marine cloud brightening (MCB), and exploring methods to reduce carbon emissions from human activities.

The research coincides with growing global interest in cloud engineering. UK Research and Innovation has recently initiated a £10.5m research program aimed at providing policymakers with information on solar radiation management methods, including Marine Cloud Brightening (MCB). Meanwhile, the Advanced Research and Invention Agency (ARIA) is dedicated to researching technologies for climate and weather control. A team from the University of Washington recently conducted its inaugural outdoor aerosol experiment in Alameda, California, using a retired aircraft carrier.

Journal Reference: Ying Chen, Jim Haywood, Yu Wang, Florent Malavelle, George Jordan, Amy Peace, Daniel G. Partridge, Nayeong Cho, Lazaros Oreopoulos, Daniel Grosvenor, Paul Field, Richard P. Allan, Ulrike Lohmann. Substantial cooling effect from aerosol-induced increase in tropical marine cloud cover. Nature Geoscience, 2024; DOI: 10.1038/s41561-024-01427-z