Biochar, in soil tilled in a test farm at the BioCentury Research farm in Des Moines, Iowa, U.S.A. Biochar is the result of burning biomass and, when added to soils, it can sequestrate its carbon for hundreds or thousands of years. Therefore, it is considered a negative emissions technology. Source: National Renewable Energy Laboratory.
Negative emissions, also known as carbon dioxide removal, refers to processes by which carbon emissions are sequestered in an effort to a) prevent additional accumulation of greenhouse gases in the atmosphere, and/or b) remove greenhouse gases that have accumulated in the atmosphere. If carbon emissions are sequestered at higher rates than they are emitted, the overall greenhouse gas concentration in the atmosphere could be reduced. Many scenarios that consider how to reduce emissions at the speed and scale required to meet warming targets below 2ºC expect that negative emission strategies will play some role. However, many of these strategies should come secondary to avoiding emissions to begin with, as they have significant economic and justice implications. Negative emissions can be achieved biologically by increasing natural carbon sinks or through chemical engineering processes. Negative emissions approaches can be classified into the following main categories (EASAC, 2018):
- Afforestation and reforestation
- Land and soil management
- Carbon Capture and Storage (CCS)
- Bio Energy with Carbon Capture and Storage (BECCS)
- Direct Air Capture (DAC)