This report focuses on the timescales of climate reversibility under a range of Bio-Energy with Carbon Capture and Storage (BECCS) scenarios. The experiments performed here are based around a narrative that emissions are strongly mitigated over the 21st century with a view that climate forcing is stabilised by 2100 but the 2°C target is missed.
Key Policy Points
- Three enhanced BECCS scenarios are considered post 2100. One involves extreme tropical deforestation (18% of the land surface), another moderate deforestation (4%) and a third the use of abandoned agricultural land (5%) to grow bio-crops. All scenarios assume no land-use change between 2005 and 2100 and no use of BECCS until after 2100. The reference scenario assumes no BECCS. These scenarios assume annual first generation bio-energy crops.
- BECCS contributes between 1.7 [6.23 GtCO2/yr] and 8 GtC/yr [29.3 GtCO2/yr] in negative emissions by 2200.
- Against a background mitigated world with 4.2GtC [15.4 GtCO2/yr] of net fossil fuel and industry emissions (post 2100) only the ‘extreme’ BECCS scenario leads to net negative emissions and thus cooling. More moderate BECCS deployment offset some but not all of the warming caused by fossil fuel emissions.
- Land-use emissions from land clearance offset some of the negative emissions from BECCS. On short timescales this can lead to overall warming; on a longer timescale negative emissions dominate land-use emissions.
- The timescale of land-use emissions is important, in a scenario with rapid land clearance for BECCS, emissions from land clearance lead to an initial warming above the reference scenario. The same scenario with slower BECCS deployment reduces this initial additional warming.
- Selection of land plays an important role. The use of lower productivity abandoned land with lower embedded land-use emissions is likely to lead to less initial warming than clearance of high productive forest. However, on long timescales the more productive land is likely to have the greatest level of net negative emissions. This effect is likely to be important in emission scenarios which overshoot and rely on negative emissions.
- In the ‘extreme’ BECCS scenario temperatures are above the reference ‘no BECCS’ scenario until 2150 and do not return to 2100 levels until 2225. After 200 years temperatures are still not below 2°C having reached an overall peak of just over 3°C.
- Reversing climate change with BECCS may therefore involve very long timescale and large scale deployment of both bioenergy crops and technology.