Carbon Dioxide Removal (CDR) Methods: BECCS Part 1

The journey to a world where global temperatures in 2100 are only 2^oC warmer than pre-industrial times has been painted in an assortment of colours. From the rosy glow of a renewable rich world where global emissions steadily decrease, to the bleaker grey of rising emissions requiring ‘last ditch’ attempts to bring the world back from the brink, the possible pathways are numerous.

Rosy vs grey pathways (Tollefson, 2015)

Most commonly used are the IPCC scenarios. In particular, the scenario named RCP 2.6, representing a potential pathway for us to meet the target of 2^oC by the end of the century. However, this pathway relies heavily on the removal of CO₂ from the atmosphere to produce negative emissions; where we take away more emissions than we put into the atmosphere. Even in the best case scenario, some sources can’t become carbon neutral, so CO₂ will need to be removed to counteract this. Personally, this feels rather like CDR territory…

The novel picture below taken from ‘The 2^oC dream’ highlights the settings for the global thermostat; fuels=green, CCS=max, forests=max, CO₂=less than 450 parts per million. The green energy, maximum forest cover and capped CO₂ did not come as a surprise, but the carbon capture and storage (CCS) certainly did. CCS prevents CO₂ from power plants entering the atmosphere. Inside the power plant CO₂ is removed, compressed into a liquid and injected into storage sites deep below the ground. However, CCS alone is not a form of geoengineering because the carbon is removed before it gets to the atmosphere. 

The global thermostat in 2100 (Tollefson, 2015)

 

Does this make geoengineering irrelevant? 

To produce the negative emissions seen in the RCP2.6 scenario, CCS has to be coupled with bioenergy to remove atmospheric carbon. Together they are known as bioenergy with carbon capture and storage (BECCS). This is geoengineering. Bioenergy involves growing biomass (e.g. plants) which take in atmospheric CO₂ through photosynthesis over their lifetime. Using this biomass to make energy, fuel or within chemical production would release the CO₂ back into the atmosphere (see diagram below), but not if it is captured and stored. Currently, only one large scale demonstration plant  is in existence but as the video below shows there are big ideas for expansion.

Comparison of emissions produced by different fuels (Kemper, 2015)   Next week I will look at BECCS in more detail and give my opinion on this technology. If you already have thoughts or considerations on BECCS please leave a comment!