The Marine Cloud Brightening Project is an open, international collaboration of atmospheric scientists and other experts to advance understanding of cloud responses to aerosol particles – a critical part of understanding the climate, and a critical area in which human activities are thought to cause significant effects.

We seek to advance scientific understanding in this area by developing a framework and associated technology that will allow the scientific community to conduct experiments to understand cloud processes with a much greater degree of control than has previously been possible.

To do this we propose to:

  1. Develop new models and improve existing models of aerosol-cloud interactions needed for accurate modeling of climate and climate change.
  2. Use advanced techniques such as machine learning to analyze cloud-aerosol data to test and inform models.
  3. Develop spray technology that will generate controlled volumes and sizes of tiny sub-micrometer seawater particles in sufficient numbers to increase the local brightness of low clouds in a marine environment.
  4. Conduct small-scale, controlled field experiments with to provide new understanding of the interactions between aerosols and clouds.


Clouds reflect solar radiation (sunlight) back to space, producing cooling effects locally, and on the planet. The reflectivity of clouds increases as the number of water droplets inside the cloud increases and their size decreases, making the clouds brighter and longer lasting, reflecting sunlight and increasing cooling.

Aerosol particles in the atmosphere are ubiquitous and arise from many sources, both natural (wind blown dust, biological emissions, sea spray) and human (combustion engines, fossil fuel power plants). As these particles mix into low clouds, particularly those over the ocean, they alter the properties of clouds by adding droplet nuclei, catalyzing more small droplets to form and brightening the clouds. The large quantities of man-made particles produced by industrial activity are likely to be cooling the planet enough to significantly off-set warming caused by greenhouse gases, but this effect is not well quantified. The impact of aerosol particles on clouds remains one of the major sources of uncertainty hindering projections of climate change over this century.

In 1990, cloud physicist John Latham proposed the idea that the amount of solar radiation reflected by clouds might be deliberately increased by augmenting the existing population of aerosol particles with salt particles created from seawater. Marine cloud brightening, as it is now termed, has been suggested as a possible approach to intentionally modifying the Earth’s climate (“climate intervention” or “climate engineering”) in order to counteract anthropogenic global warming. Marine cloud brightening is receiving increasing attention from the scientific community, and is now considered one of the potentially feasible approaches to climate intervention.


Our current lack of knowledge about how aerosols interact with clouds is hindering progress both in quantifying the amount of greenhouse warming being counter-balanced by aerosol increases, and in understanding the potential efficacy of marine cloud brightening.

Significant gaps in our basic understanding of the physical processes that control clouds, and the degree to which clouds are sensitive to anthropogenic emissions are exacerbated by a lack of controlled experiments. Although we have developed and now use increasingly sophisticated technology to observe cloud properties, our focus to date has been observing clouds as they occur in nature. Consequently, we lack control of experimental conditions that is a fundamental component of the scientific method.

When studying cloud processes, we are unable to perform an experiment in which we know the exact quantities and properties of particles mixing with clouds, and thus cannot make robust estimates of their relationships. Furthermore, we cannot test our findings by performing the same experiment repeatedly, because we cannot reproduce the particle inputs. This lack of control is especially problematic when trying to study interactions between aerosol particles and clouds because not only the particle concentrations, but the chemistry (type of particles) and cloud processes are experimentally uncontrolled.

The marine cloud brightening project includes computer modeling and data studies alongside a series of small-scale experiments in which particle number and chemistry are controlled over limited areas. By injecting known quantities of particles into the marine boundary layer, we will be able to observe the impact of the particles on cloud properties and contrast those properties with the properties of clouds formed in the natural background. The final experiment in the program, the Marine Cloud Limited Area Field Experiment, is described in the 2009 Special Issue of the Philosophical Transactions of the Royal Society and 2015 report from the National Academy of Sciences National Research Council. Its methodology and scale are similar to recent major observational studies of pollution effects on clouds, ORACLES and VOCALS, but with the ability to control and accurately model and measure aerosol particle inputs and their effects.


The Marine Cloud Brightening Project is an open, multi-institutional research collaboration within the Atmospheric Intervention Research (AIR) Program at the University of Washington. It operates in partnership with Palo Alto Research Center (PARC) where work is being undertaken to develop spray technology, and Pacific Northwest National Laboratory, a center of excellence for climate modeling.

In addition to the scientific goals of the research, it is the explicit intent of this team to conduct research in Marine Cloud Brightening in such a way that it can function as an exemplary model for open, objective, small scale field research programs in atmospheric science that provide objective information to inform policy.

MCB Project