David Kramer’s article “Negative carbon dioxide emissions” (Physics Today, January 2020, page 44) provides an excellent overview of the pros and cons of several climate-ameliorating interventions in the global carbon cycle. But it overlooks what ought to be at the top of our list: protection of natural carbon sinks.
Over the past decade, natural sinks have removed from the atmosphere about 5 gigatons of carbon per year, with approximately three-fifths going to the oceans and the rest to terrestrial ecosystems. That removal rate is about one-half of annual anthropogenic emissions worldwide. And nature does it for free!
That natural sink strength is far greater and far cheaper than any engineered scheme can promise to deliver over the coming two or three decades. If the strength is maintained, a 50% reduction in today’s emissions would stabilize atmospheric carbon dioxide; with a further reduction in emissions, atmospheric levels would decline over time, albeit at an ever-decreasing rate.
Unfortunately, natural sinks are threatened today by a combination of deforestation, soil erosion, ocean acidification, agricultural malpractices on prime land, increasing exploitation of poorer quality lands for food production, and climate change itself. Yet on farmland, protection and augmentation of natural sinks can even increase crop yields.
The most important thing we can do to sequester carbon is to prevent the degradation of existing, priceless, and cost-free natural sinks. Combined with rapid deployment of renewable energy, they might give us a chance to prevent climate catastrophe.
