Scientists warn against over-relying on carbon removal to achieve net-zero

An international team of researchers has highlighted the risk of relying too much on carbon removal technologies to limit climate change in a new study published in Nature.

Carbon removal technologies are often seen as a great solution to the challenge of limiting global warming to within 2°C above pre-industrial levels.

However, the detrimental effects of climate change on crop yields could reduce the capacity of large-scale bioenergy with carbon capture and storage (BECCS) and threaten food security, creating an unrecognised positive feedback loop on global warming, the study says. 

The team behind the research comprises scientists from the Vienna-based International Institute for Applied Systems Analysis (IIASA), Fudan University in Shanghai, China, and several other institutions around the world. 

Using the shared socioeconomic pathways of climate mitigation, the researchers designed a number of scenarios in which the deployment of large-scale mitigation technologies and BECCS starts in different decades, from 2030 to 2100, and considered technical solutions to food shortages including cropland expansion, nitrogen fertiliser intensification, nitrogen use efficiency enhancement, afforestation, and international food trade.

The feedback on future climate change and food shortages caused by reduced BECCS potential was quantified using an Earth System model and as a function of the delayed mitigation.

“Although in our study we focused on only one carbon removal technology – BECCS – and showed how it will likely be limited because of harmful climate feedbacks, it is entirely possible that other technologies have similar limitations,” said IIASA researcher, Thomas Gasser, one of the study authors.

“Therefore, over-reliance on such unproven technologies when designing climate policies means taking the risk of simply failing to reach one's goal. The solution may be to diversify the technologies (to spread the risks out), but primarily it is to rely on conventional mitigation approaches, that is, to lower energy demand and consumption, and develop a sustainable clean energy supply.”

The simulation results showed that the feedback of biomass-based carbon removal technologies could have a significant impact on the long-term trend of future climate change.

For example, when large-scale mitigation and BECCS are delayed from 2040 to 2060, the reducing yields of agricultural residue for carbon removal technologies could in turn increase global warming from 1.7°C to 3.7°C by 2200. Of this 2°C increase, 0.8°C is attributable to the loss of BECCS capacity caused by the feedback that had been ignored so far, while the remaining 1.2°C are attributed to the delayed mitigation itself.

Moreover, the increase in global temperatures would be accompanied by a decline in global average daily food calories per capita from 2100 to 1500 kilocalories per day, on average. 

The results also indicate that when climate mitigation is delayed from 2040 to 2060, the number of developing countries that see a domestic food supply gap would increase from 81 to 90 in 2100. As a result, early climate mitigation or regional population migration might be the only solution to satisfy food demand if the projected food trade failed to be achieved.

The team behind the study has stressed, however, that if carbon removal technologies relying on biomass could be widely deployed in the short term, there is still hope to alleviate both global warming and a food crisis.