Why CO2 removal is not equal and opposite to reducing emissions. The requirement to reach zero carbon dioxide (CO2) emissions to stop the rise in global average temperatures arises from the long time that CO2 stays in the atmosphere and the slow reaction time of the ocean. But how about the “net” aspect? The logic is that residual emissions of CO2 – and other greenhouse gases that are challenging or very costly to eliminate – can be balanced by removing CO2 directly from the atmosphere and storing it for the long term. This can be achieved by enhancing natural carbon “sinks” that remove CO2 from the atmosphere – for example, by planting trees or restoring peatlands and mangrove forests. Other ways to remove CO2 from the atmosphere include capturing CO2 from bioenergy plants or engineered methods that capture CO2 directly from the atmosphere and store it underground or in products. An assumption that is commonly made when balancing a CO2 emission with a CO2 removal is that “one tonne in equals one tonne out” – that is, that the behaviour of the climate system in response to emissions and removals is “symmetrical”. But this assumption had not been tested, and – while likely reasonable for small emissions and removals – it seemed unlikely to hold for larger emissions and removals due to the non-linear nature of the Earth system. In a new paper, published in Nature Climate Change, my colleagues and I show that the climate response to emissions and removals is actually “asymmetrical” – that is, the carbon cycle and climate response to CO2 emissions is not equal and opposite to CO2 removals of the same magnitude.
Carbon Brief 21st June 2021 read more »