"The Intergovernmental Panel on Climate Change concluded last year that reaching a key emissions goal—roughly equivalent to limiting warming to 2°C by 2100—would rely on the deployment of one or several CDR technologies. Deploying them could cost more than a trillion dollars, one expert estimates.<p>The new study puts the concept of CDR to the test—without getting into the specifics of which technology to use. The authors used computer simulations to figure out what would happen if engineers removed a whopping 5 gigatons of carbon dioxide from the atmosphere each year. Achieving that goal, equivalent to removing roughly half the amount of CO2 that is now emitted from manmade sources, would require a gargantuan global effort. (To visualize the scale, imagine 5000 new facilities each roughly the size of a sports stadium.)<p>Yet the scientists found the environmental benefits of such a massive technological campaign were surprisingly small, especially in terms of protecting the ocean from the impacts of climate change. One key impact of rising CO2 levels is seen in the pH of ocean waters—the global sea surface has been acidified by roughly 0.1 units and impacts on marine shells are beginning to show. But the experiment demonstrated that the CDR campaign had only limited effect to reverse that trend: Without the CDR the surface pH was reduced by 0.75 units by 2200; with CDR the acidification was reduced 0.7 units, the team reports online today in Nature Climate Change."