July 11, 2013
Cloud Seeding Proposed To Protect Coral Reefs
April Flowers for redOrbit.com - Your Universe Online
New research from the University of Leeds reveals threatened coral reefs could be protected from bleaching by warming oceans. The study proposes a targeted version of the geoengineering technique known as Marine Cloud Brightening (MCB) - seeding the clouds to cool sea surface temperatures - could give coral a fifty year "breathing space" to recover from acidification and warming.
"Coral bleaching over the last few decades has been caused by rising sea temperatures and ocean acidification," said Dr Alan Gadian from Leeds University. "Our research focuses on how Marine Cloud Brightening could quickly lower sea temperatures in targeted areas."
A strong link exists between warmer-than-normal sea temperatures and cases of coral bleaching, which is most likely to occur when a 1 degree Celsius temperature rise happens over a prolonged period. This period is typically 12 weeks.
Unmanned vehicles spray tiny seawater droplets to brighten clouds. These droplets rise into the cloud, increasing the reflectivity and duration. More sunlight is bounced back into space by these highly reflective clouds, resulting in a cooling sea surface temperature.
Originally envisaged as a global counter measure against warming, in principle MCB could be more targeted. Dr Gadian suggested in 2012 MCB could be used in the Atlantic to tame hurricanes.
The focus of the new modeling is on the impact of seeding marine stratocumulus clouds over the Caribbean, French Polynesia, and the Great Barrier Reef. The researchers show how the projected increases in coral bleaching that were caused by rising CO2 levels were eliminated while sea surface temperatures cooled to pre-warming levels.
The model projected mild and severe coral bleaching events over a 20 year period for the three regions, showing without the use of MCB the amount of coral bleaching was severe. The simultaneous deployment of MCB, however, eliminated the risk of extra bleaching. The results of this study were published in Atmospheric Science Letters.
"We estimate that MCB would have an annual cost of $400 million, however political, social and ethical costs make a true figure difficult to estimate, said Gadian. "Whatever the final figure, it will be less expensive than the damage the destruction of coral would wreck on neighboring countries, the local food chain and global biodiversity."
The development of geo-engineering projects remains subject to public and political skepticism. However, as MCB is the least disruptive form of Solar Radiation Management, the research team believes small-scale use of MCB for conservation would be unlikely to generate public opposition.
Gadian and his colleagues propose field testing MCB on a scale of 100 square meters. This could demonstrate its use without producing significant climate effects. The main disadvantage of this technique, aside from cost, is that it would not address ocean acidification, which is a direct result of CO2 emissions.
"Reducing and removing atmospheric CO2 remains the long term solution to acidification and warming oceans, however, even if this process began tomorrow the coral may be destroyed by the time we see the results," concluded Gadian. "Our results show that targeted use of cloud brightening could offer a short term breathing space, which could be vital for countries which rely on corals for their livelihoods."