We recently looked at problems with a last resort solution to counteract global warming by artificially shading the Earth from sunlight by injecting sulphur or small, reflective particles into the upper atmosphere. Now a new study from the Carnegie Institution has thrown further doubt on the effectiveness of such a proposal. Although it may lower the planet’s temperature by a couple of degrees, it would do little to stop the acidification of the world’s oceans that threatens coral reefs and other marine life.

According to the Carnegie Institution, the main problem with trying to shade the Earth is that it addresses the symptoms rather than the cause. That is, it deals with the warming of the Earth’s atmosphere rather than the amount of carbon entering the atmosphere. The institution's research found that the slight reduction in carbon dioxide (CO2) was not enough to make a big difference to ocean acidification. This is in spite of land plants being expected to grow more vigorously in a high-CO2, cool environment, which enables them to hold onto more carbon.

Ocean acidification rivals global warming as a threat to marine ecosystems, especially coral reefs, which need to be surrounded by mineral-saturated water in order to grow. Rising levels of CO2 make seawater more acidic, leading to lower mineral saturation. The Carnegie research team believe that continued CO2 emissions will cause coral reefs to begin dissolving within a few decades, putting the survival of these ecosystems at extreme risk.

The research team points out that the minimal effect of geoengineering on ocean acidification adds weight to its argument against tampering with the planet's complex and finely tuned climate system. Critics warn that such a scheme might also alter rainfall patterns, damage the planet's ozone layer or have other unexpected effects.

The study by researchers at the Carnegie Institution appears in the journal Geophysical Research Letters.