Cloud Seeding: A Geo-Engineered Response to Climate Change?

December 10, 2013

Clouds, air pollutants, and the underlying landscapes all impact Earth’s energy budget in complex and competing ways.  Atmospheric scientists from Yale and Tokyo’s Todai University gathered at a YCEI sponsored forum in September to share how they use climate models to study how humans affect this nuanced system—and how we can possibly counteract global warming by manipulating cloud formation.

Though high-altitude cirrus clouds reflect some incoming solar radiation, they also strongly absorb heat radiated from the Earth’s surface, causing temperatures to rise.  Some climate scientists argue that dispersing tiny aerosol particles in the atmosphere would allow the ice crystals that make up cirrus clouds to grow larger, and thus fall faster, reducing the cloud lifetime.  Altering clouds with particle injection would thus reduce cirrus coverage and allow more heat to escape the earth.

Yale scientist Trude Storelvmo recently tested this thought experiment with a global climate model.  At the YCEI forum, Professor Storelvmo shared how releasing aerosols in mid to high latitude regions could cool surface temperatures to pre-industrial levels.  Her model results show that the interactions of cirrus clouds and aerosol particles, such as mineral dust or bismuth tri-iodide, can reduce cloud lifetimes and their warming effects on Earth.

The technique is not without risks, warned Storelvmo.  Seed too few particles and the effects won’t be strongly felt; too many and the particles may overstimulate cloud growth, heating the planet.  Done properly, however, cloud seeding could undo decades of warming.  

Will drones expel aerosols in the sky in the near future?  Though Storelvmo is not a proponent of employing the cirrus cloud seeding technique, she believes that being prepared with a scientifically sound, environmentally safe response to climate change is invaluable.  Her experiment in geo-engineering demonstrates the power of climate simulation: scientists can test daring ideas risk-free, translating provocative proposals into numerical terms.


Other scientists at the climate forum have used modelling to study the atmosphere on a broad range of scales, from cloud-aerosol microphysics to global landscape-atmosphere interactions.  Yutaka Kondo of the University of Tokyo presented his findings on the effects of aerosols on climate in East Asia.  Dr. Kondo explained how the radiative effects of clouds—whether they will cool or warm the planet—are determined by interactions of particles and water droplets.  Different air pollutants support the growth of different cloud types.

Dr. Kondo stressed the importance of taking emissions inventories around the globe to determine the dominant cloud formation mechanisms, since aerosol properties vary greatly from place to place.  This could be critical for advancing aerosol parameterizations in climate models and more accurately projecting future climate.

Nadine Unger, Associate Professor at the School of Forestry and Environmental Science and the Geology and Geophysics department, also discussed aerosol research, emphasizing in her presentation the importance of chemical reactions that take place in the atmosphere.  Since land ecosystems are the major source of reactive carbon for the atmosphere, Professor Unger’s current projects seek to understand the global temperature response to land use and land cover changes.  She has helped develop the Yale-E2 global carbon-chemistry-climate model to meet this goal.  

Dr. Unger has designed her studies in such a way to maximize their relevance to government policy.  She compared the climate forcing contributions of various economic sectors, such as agriculture or shipping, so that governments can understand the most efficient ways to limit global warming and make smart policy decisions. 

The Yale and University of Tokyo climate research communities are at the forefront of understanding how atmospheric dynamics control global temperatures.  These scientists may be working with theoretical models, but their research is grounded in reality and is aimed at applications.  Their presentations inspired hope that with informed changes to human aerosol contributions, climate balance may be restored