Shading Earth won’t stop ocean acidification

Geoengineering is the idea that humans can slow, stop or reverse the effects of climate change by altering the composition of Earth’s atmosphere and biosphere.  While controversial, these methods, including reducing sun exposure by injecting aerosols into the atmosphere or using giant mirrors to reflect the sun’s rays, were identified as a high-priority area for research by the G8-5 nations.

Ken Caldeira of the Carnegie Institution, however, has identified at least one major weakness of using reflective particles (sulfur, which mimic conditions following volcanic eruptions) to reflect sunlight away from the Earth.  In a paper in the May Geophysical Research Letters, he and his colleagues show that although this technique could lower Earth’s temperatures, it will do almost nothing to curb rising carbon dioxide levels in the atmosphere. CO₂ will thus continue to be absorbed by oceans, creating acidic conditions that harm marine wildlife.

Previous studies have shown that shading the Earth with aerosols would increase global precipitation. Terrestrial plants might grow more vigorously in a cooler, wetter world, according to Caldeira’s simulation model, and thus sequester more carbon. But this small effect would not be nearly enough to make a big difference, says Caldeira.  Higher acidity leads to lower levels of minerals in seawater, which is a death sentence for mineral-dependent corals.

Of course, Caldeira recommends cutting carbon dioxide emissions as the best solution to the problem.  In a statement, he said:

“One of the good reasons to prefer CO₂ emissions reductions over geoengineering is that CO₂ emissions reductions will protect the oceans from the threat of ocean acidification, whereas these geoengineering options will not.”

But if regulations on carbon emissions are so slow to come — such as in the slow-but-steady Waxman-Markey climate bill — and if a startling number of people still don’t believe that climate change is real, how can we expect swift and comprehensive action to curb CO₂ emissions?  Shouldn’t we have emergency backup plans, like geoengineering?  Or will the development of these technologies give humans a green light to keep polluting?

Matthews, H. D., L. Cao, & K. Caldeira (2009). Sensitivity of ocean acidification to geoengineered climate stabilization Geophysical Research Letters