Marine Cloud Brightening Project

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. We specifically are interested in exploring the potential for intentionally brightening marine low clouds by augmenting the natural marine aerosol particle population. The project is a collaboration with a number of scientists and engineers to advance the technology and scientific understanding of marine cloud brightening as a tool that may help limit the warming caused by anthropogenic greenhouse gases. The research we’re conducing will also help us better understand processes that currently the source of the leading uncertainty in how humans are driving climate change: namely, how pollution aerosol particles affect clouds and climate.

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 have efforts to:

  1. 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 [see article in IEEE Spectrum]
  2. conduct limited area (small-scale) field experiments with the spray technology to provide new understanding of the interactions between aerosols and clouds, very similar in nature to the highly regarded VOCALS observational study, but with the ability to control and accurately model and measure aerosol particle inputs and their effects, and employing new observational tools (e.g. drones and small-scale instruments)
  3. develop new models and improve existing models of aerosol-cloud interactions needed for accurate modeling of climate and climate change
  4. use observations of aerosol-cloud interactions, such as from ship emissions, that are already brightening low marine clouds in order to constrain the expected response from intentional aerosol injection
  5.  explore leading-edge analytical approaches, such as machine learning, to study the potential efficacy and effects of marine cloud brightening

The Importance of Controlled Field Studies of Clouds & Aerosols

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 will include 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 MCB Limited Area Field Experiment is described in an article in Climatic Change and mentioned in the recent Special Issue of the Philosophical Transactions of the Royal Society and the recent report from the National Academy of Sciences National Research Council. 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.

Clouds, Climate Impacts and Climate Intervention

Clouds reflect solar radiation (sunlight) back to space, producing cooling effects locally, and across 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 clouds over the ocean, they alter their properties by adding droplet nuclei, catalyzing more small droplets to form and brightening the clouds. The large quantities of man-made particles currently produced by industrial and other human activities are likely cooling the planet enough to be 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 quantification of how much and by what mechanisms humans have driven 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.


pdf Microphysical, macrophysical and radiative responses of subtropical marine clouds to aerosol injections, Chun, J.-Y., Wood, R., Blossey, P., and Doherty, S. J.: Atmos. Chem. Phys., 23, 1345–1368,, 2023.

pdf Simulating aerosol lifecycle impacts on the subtropical stratocumulus-to-cumulus transition using large eddy simulations. Ehsan Erfani, Peter Blossey, Robert Wood, Johannes Mohrmann, Sarah Doherty, Matthew Wyant, Kuan-Ting O. J. Geophys. Res.: Atmospheres, 127, e2022JD037258., 2022.

pdf Global Reduction in Ship-tracks from Sulfur Regulations for Shipping Fuel. Tianle Yuan, Hua Song, Robert Wood, Chenxi Wang, Lazaros Oreopoulos, Steven E. Platnick, Sophia von Hippel, Kerry Meyer, Siobhan Light, Eric Wilcox. Science Advances, 8(29), eabn7988., 2022.

pdf Opinion: To assess marine cloud brightening’s technical feasibility, we need to know what to study—and when to stop. Michael S. DiamondAndrew GettelmanMatthew D. LebsockAllison McComiskey, Lynn M. RussellRobert Wood, and Graham Feingold.

pdf Opportunistic Experiments to Constrain Aerosol Effective Radiative Forcing. Christensen, M., Gettelman, A., Cermak, J., Dagan, G., Diamond, M., Douglas, A., Feingold, G., Glassmeier, F., Goren, T., Grosvenor, D., Gryspeerdt, E., Kahn, R., Li, Z., Ma, P.-L., Malavelle, F., McCoy, I., McCoy, D., McFarquhar, G., Mülmenstädt, J., Pal, S., Possner, A., Povey, A., Quaas, J., Rosenfeld, D., Schmidt, A., Schrödner, R., Sorooshian, A., Stier, P., Toll, V., Watson-Parris, D., Wood, R., Yang, M., and Yuan, T. Atmos. Chem. Phys. 22, 641–674,, 2022.

pdf  Assessing the potential efficacy of marine cloud brightening for cooling Earth using a simple heuristic model. Robert Wood. Atmos. Chem. Phys., 21, 14507–14533,, 2021.

Cloud Brightening from Shipping in Subtropical Low Clouds.
Diamond, M. S., H. M. Director, R. Eastman, A. Possner and R. Wood, 2020: Substantial. AGU Advances1, e2019AV000111.
[AGU Advances Editor Highlight].

pdf The efficacy of aerosol–cloud radiative perturbations from near-surface emissions in deep open-cell stratocumuli. 
Possner, A., Wang, H., Wood, R., Caldeira, K., and Ackerman, T. P.: Atmos. Chem. Phys.18, 17475-17488, 2018.

pdf The Geoengineering Model Intercomparison Project –introduction to the second special issue. Ben Kravitz, Alan Robock , Olivier Boucher, Mark Lawrence , John C. Moore , Ulrike Niemeier, Trude Storelvmo,  Simone Tilmes, and Robert Wood. Atmos. Chem. Phys., doi:10.5194/acp-special_issue376-preface, 2018.

pdf  The efficacy of aerosol–cloud radiative perturbations from near-surface emissions in deep open-cell stratocumuli. Possner, A., Wang, H., Wood, R., Caldeira, K., and Ackerman, T. P.: Atmos. Chem. Phys., 18, 17475-17488, 2018.

pdf Could geoengineering research help answer one of the biggest questions in climate science? Robert Wood, Thomas Ackerman, Philip Rasch and Kelly Wanser. Earth’s Future.  5, 659–663,doi:10.1002/2017EF000601, 2017.

pdf Large-Eddy Simulation of Ship Tracks in the Collapsed Marine Boundary Layer: A Case Study from the Monterey Area Ship Track Experiment. A. H. Berner, C. S. Bretherton, and R. Wood. Atmos. Chem. Phys., 14, 5851-5871, doi:10.5194/acp-15-5851-2015.

pdf Climatic change special issue: Geoengineering research and its limitations. Robert Wood, Stephen Gardiner and Lauren Hartzell-Nichols. Climatic Change, 121, 427-430, DOI 10.1007/s10584-013-1000-4, 2013.

pdf Defining success and limits of field experiments to test geoengineering by marine cloud brightening. R. Wood and T. P. Ackerman. Climatic Change, 121, DOI 10.1007/s10584-013-0932-z, 2013.

pdf Factors determining the most efficient spray distribution for marine cloud brightening, P. J. Connolly, G. B. McFiggans, and R. Wood. Phil. Trans. R. Soc. A372: 20140056., 2014.

pdf Marine Cloud Brightening. J. Latham, K. Bower, T. Choularton, H. Coe, P. Connolly , G. Cooper ,T. Craft, J. Foster, A. Gadian, L. Galbraith, H. Iacovides, D. Johnston, B. Launder, B. Leslie, J. Meyer, A. Neukermans, B. Ormond, B. Parkes, P. J. Rasch, J. Rush, S. Salter, T. Stevenson, H. Wang, Q. Wang, and R. Wood. Phil Trans Roy. Soc. A, 2012, 370, 4217-4262, doi: 10.1098/rsta.2012.0086, 2012.

Professor, Atmospheric Sciences, Univ. of Washington