What are "negative emissions"?

To reach zero net emissions (see: What does “zero net emission” mean?) and limit global warming to 1.5°C, it is necessary to remove and permanently store CO₂ from the atmosphere. This is called Carbon Dioxide Removal (CDR). As it is the opposite of emissions, these practices or technologies are often described as achieving "negative emissions" or "sinks". There is a direct link between zero net emissions and CDR: The earlier zero net emissions are achieved, the less CDR is necessary. Therefore, the projected amount of required CDR over the 21st century varies from 100 to 1'000 Gt CO₂.

CDR can be divided into the three main groups: biological, technological and geochemical processes.

 

Biological CDR enlarges natural sinks and includes several measures. Examples are:

  • Afforestation and forest management, i.e. large-scale plantation of trees which store carbon in soil and biomass.
  • Adapted land management to increase and permanently fix C from atmospheric CO2 in the soil. One example is to renature peatlands.
  • Pyrolysis of biomass to form charcoal (biochar) that keeps carbon in the soil for many years.

 

Examples of technological CDR are:

  • Removing CO2 directly from the exhaust gases of industrial processes and storing it elsewhere, e.g. underground (Direct Air Capture with Carbon Storage, "DACCS").
  • Bioenergy utilization in combination with carbon capture and storage means burning biomass in power plants, immediately capturing the CO2 underground (Bio-Energy with Carbon Capture and Storage, "BECCS"). This process combines biological and technological CDR.

 

Geochemical CDR includes measures such as:

  • Enhanced weathering
  • Increasing ocean productivity

 

Technological and geochemical processes for carbon dioxide capture have been little tested so far and any negative side effects for ecological and social sustainability must be taken into account. Therefore, myclimate currently sees the highest potential and the best cost-benefit ratio for biological processes, i.e. projects based on soil-based negative emissions, such as reforestation , soil management, and the restoration of coastal wetlands and peatlands.

But research into these techniques continues to be pushed as the later the goal is achieved (zero net emissions) the higher the negative emissions will need to be.

 

How to keep glob­al warm­ing below 2°C. Source: MCC.

Sources:

  • IPCC 2018 Special Report 15; Mark Jacobsen (Energy and Environmental Science 2, 2009)
  • EASAC 2018. Negative emission technologies: What role in meeting Paris Agreement targets? Policy report 35.
  • IPCC 2019. Special Report on Climate Change and Land.
  • IPCC 2018. Special Report 15. Global Warming of 1.5°C.
  • Mercator Research Institute on Global Commons and Climate Change (MCC) 2016. Vorsicht beim Wetten auf Negative Emissionen. MCC-Kurzdossier Nr. 2.
  • Stiftung Risiko-Dialog 2019. The role of atmospheric carbon dioxide removal in Swiss Climate policy.

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