Marine cloud brightening could help weaken hurricanes like Sandy

SAN FRANCISCO, Dec. 6, 2012  /PRNewswire/ -- In a recent study, atmospheric scientists from the National Center for Atmospheric Research in the US, and the Universities of Manchester, Leeds and Edinburgh, UK, found that cooling ocean surfaces by brightening clouds with a sea-salt spray mist ("Marine Cloud Brightening") could reduce the intensity of hurricanes. It is possible that the largest hurricanes and hybrid storms could be prevented, saving billions in damage and preventing the associated loss of life.

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Cool the ocean surface to weaken storms when as they form
The study, Weakening Of Hurricanes Via Marine Cloud Brightening, published in the British journal Atmospheric Science Letters, uses computer models to study the potential effects of cooling the ocean surface waters in regions where hurricanes spawn and start to develop. Since heat from ocean surface waters supplies hurricanes with their energy for growth, a reduction in ocean surface water temperature in the places hurricanes start to develop leads to weaker hurricanes with lower wind-speeds – storms that would cause less damage. 

Cool the ocean surface by brightening the clouds above
Thin, low-level clouds (called stratocumulus) cover vast areas of the oceans. They affect climate strongly because they bounce back into space about half the sunlight that lands on them. If the clouds weren't there the Earth would be much warmer. These clouds also cool the ocean surface waters below them. Like a white umbrella, the brighter these clouds, the more sunlight they reflect away from the water, causing it to cool.

Brighten clouds with sea-salt mist
The idea proposed by the researchers is to increase the reflectivity of the stratocumulus clouds above ocean surface waters by misting them with large quantities of tiny salt-particles (of about one-millionth of a meter in size). These tiny salt particles enter the cloud and cause new small cloud droplets to form on them, increasing the overall number of drops in the cloud, which increases the reflective areas for sunlight to bounce from, brightening the cloud. The process mimics the effect in nature of small particles of sea mist rising from foaming sea caps to infuse clouds.

The salt mist can be generated and delivered using devices mounted on ships that sail underneath the clouds. 

Reduce the force of hurricanes
Modeling effects using one of the world's most highly regarded global climate models, the climate ocean atmosphere coupling model (HadGEM1), researchers found that misting a modest area of clouds over selected ocean surface areas could reduce the average sea-surface temperature by two or three degrees centigrade, and decrease the intensity of hurricanes that form in the region by one or two categories, indicating that if this can be done, hurricane force, and related damage, could be greatly reduced.



Other applications
Researchers are also studying Marine Cloud Brightening for applications that include helping to preserve coral reefs, increasing precipitation in dry regions, preserving arctic ice and helping to lower or maintain global average temperature as a counter to warming forces.

Recommendations 
The researchers recommend additional studies, including small localized field tests of sea-salt misting effects on clouds, to advance understanding of the feasibility and risks of these approaches. Lead researcher and theorist Professor John Latham of NCAR states, "it is our hope that we can advance understanding of what may in future be possible, but we do not advocate anything beyond research until there is a far greater understanding of these local climate systems, the effects of these techniques and, most importantly, their risks."  

The researchers also state that the type of controlled field experiments that would be most valuable to research on mitigating hurricanes are likely to produce large improvements to the accuracy of climate models, since clouds, while having large effects on climate, are not well represented.

Authors:
John Latham, National Center for Atmospheric Research, Boulder, CO: and also
University of Manchester, UK.
Ben Parkes, National Center for Atmospheric Sciences, University of Leeds, UK.
Alan Gadian, National Center for Atmospheric Sciences, University of Leeds, UK.
Stephen Salter, Dept of Engineering, University of Edinburgh, UK.

Press Contact:
Kelly Wanser – [email protected], 415-734-6790

SOURCE Atmospheric Science Letters