Guest post: Heavy use of CO2 removal would trigger high sustainability risks

Many pathways to staying beneath 1.5C delay deep cuts in carbon dioxide (CO2) emissions and rely as a substitute on big quantities of CO2 elimination (CDR) later this century.

Land-based CDR is used extensively within the 1.5C pathways offered by the Intergovernmental Panel on Local weather Change (IPCC) and in addition options closely within the local weather plans of many governments and companies.

But the large-scale deployment of land-based CDR may include main challenges. These embrace important ecological and societal dangers – notably to biodiversity loss, meals safety, freshwater use and human rights, amongst others – which haven’t been comprehensively assessed.

In our new paper, printed in Science, we assess the extent of sustainability dangers that could possibly be triggered by means of numerous totally different land-based CDR methods, corresponding to bioenergy with carbon seize and storage (BECCS) and afforestation and reforestation (A/R).

We present that dangers are triggered at a lot decrease ranges of deployment than beforehand thought. Furthermore, most of the “Paris aligned” 1.5C pathways offered by the IPCC would exceed the CDR sustainability limits outlined by our analysis.

CDR deployment in mitigation pathways 

Many mitigation pathways assessed by the IPCC envisage massive deployments of CDR all through the twenty first century. 

That is important as a result of, though the IPCC shouldn’t be “coverage prescriptive”, these pathways – and the coverage choices inside them – strongly form the “resolution house” as seen by policymakers when contemplating methods to meet the objectives of the Paris Settlement. 

The usage of CDR is especially widespread within the pathways labelled by the IPCC as “1.5C with excessive overshoot”. In these pathways, emissions cuts usually are not quick sufficient to keep away from breaching the carbon price range for 1.5C and world temperatures briefly overshoot the 1.5C restrict, earlier than intensive use of CDR brings temperatures down later this century.

Inside these pathways, CDR is deployed as much as 2050 to assist compensate for a slower transition away from fossil fuels, to scale back web emissions. When emissions attain net-zero, CDR is getting used to counterbalance massive remaining residual emissions. Past this level, it’s used to draw-down world temperature after exceeding 1.5C. 

The sort of pathway is typified by the IPCC’s “Neg” illustrative mitigation pathway. Right here, – some 5.1bn tonnes of CO2 (GtCO2) is taken out of the environment utilizing CDR in 2050 and 15.1GtCO2 in 2100. 

On this pathway, considered one of 5 outlined within the IPPC’s sixth evaluation report (AR6), main vitality from fossil gasoline drops solely 36% beneath 2020 ranges by 2050 and 73% by 2100, relative to 2020. 

This CDR and emissions profile is in sharp distinction to the IPCC’s “Ren” pathway – which depends on speedy scale-up of renewable vitality – main vitality from fossil gasoline falls 85% by 2050 and 95% by 2100, relative to 2020. (IMP-Ren) 

Which means that this renewable vitality pathway has a lot decrease reliance on CDR, which is just used to take 2.6GtCO2 out of the environment in 2050 and 3GtCO2 in 2100.

Sustainability limits 

The massive quantities of land-based CDR in most of the pathways assessed by the IPCC include important implications by way of sustainability, with the potential for severe impacts on human livelihoods and meals safety.

But the IPCC report doesn’t comprehensively assess the environmental feasibility of the eventualities, nor their related sustainability dangers. Nor does it put a determine on the size of CDR that could possibly be deployed with out triggering main impacts.

To handle this hole, we quantified the sustainability limits to the widespread deployment of BECCS, A/R and “nature-based” CDR, which incorporates restricted reforestation, forest restoration, decreased forest harvest and agroforestry.

To take action, we draw from latest research that give better consideration to the ecological, organic and societal impacts of land-based CDR.

Based mostly on these research, we calculated the degrees of CDR deployment that will set off “low”, “medium”, “excessive” and “very excessive” dangers for sustainability. These threat ranges are colour-coded from inexperienced via to darkish pink, for every kind of land-based CDR within the determine beneath.

Studying from left to proper, the determine reveals rising ranges of CDR deployment by way of GtCO2 eliminated per yr. The gray bar reveals the vary of “technical mitigation potential” for every approach, as at the moment assessed by the IPCC. The higher finish of that is the biggest quantity that might theoretically be deployed, if boundaries to speedy scale-up, constraints on feasibility and sustainability dangers usually are not taken under consideration.

The determine reveals that sustainability dangers begin nicely beneath the technical mitigation potential.

For BECCS, the IPCC stories a mean technical potential of 5.9GtCO2 per yr. But we discover that deploying greater than 1.2GtCO2 of BECCS per yr would tip over from “low threat” into “medium” or increased threat ranges.

(This determine is predicated on BECCS crops capturing a “medium” share of their related CO2 emissions, beneath 70%. For a “low” seize price beneath 50%, the low-risk threshold drops to simply 0.7GtCO2 per yr.)

Correspondingly, BECCS would cross the excessive sustainability threat threshold (proven in pink) if used to take away 1.3GtCO2 with a low seize price – or 2.8GtCO2 with a medium price.

Even these restricted ranges of BECCS assume important bioenergy coverage reforms that governments haven’t but addressed. These embrace addressing gaps in emissions accounting and guaranteeing bioenergy shouldn’t be inflicting deforestation, both immediately or not directly.  

For A/R, the IPCC common technical potential is 3.9GtCO2 a yr. Our analysis reveals that related sustainability dangers stay low or medium beneath 3.8GtCO2 per yr, with excessive dangers past that time. 

We discover that nature-based CDR (which incorporates restricted reforestation) carries the bottom sustainability dangers. Deployment would set off excessive dangers past 5.1GtCO2 a yr (together with 3.8GtCO2 per yr of non-monoculture reforestation).

Having outlined threat ranges for every kind of CDR, we then mapped these indicators onto the quantity of CDR deployed in every of the IPCC’s 5 “illustrative mitigation pathways” (IMPs).(These pathways are: gradual strengthening of local weather coverage, GS; widespread use of CDR, Neg; low vitality demand, LD; shifting pathways in the direction of sustainable growth, SP; and heavy use of renewables, Ren.)

Our outcomes, illustrated within the desk beneath, present that the three pathways that restrict warming to 1.5C with restricted to no overshoot are in a position to take action with out significantly overstepping our sustainability threat thresholds.

In distinction, Neg limits warming in 2100 to 1.5C with excessive temperature overshoot, however exceeds excessive and even very excessive sustainability threat thresholds. The GS pathway solely limits warming to 2C and nonetheless carries important ranges of sustainability dangers.

Studying the desk from high to backside, the primary set of rows checklist the change in CO2 emissions, vitality demand and fossil gasoline use in 2050 and 2100.

The second set of rows present the quantity of every kind of CDR deployed in 2050 and 2100, colour-coded based on our sustainability threat ranges.

The third set of rows present the quantity of land wanted for CDR deployment – the land footprint. Once more, these are colour-coded based on our sustainability threat ranges.

Notably, our findings present that the quantity of land wanted for CDR within the Neg pathway may attain 7.2m sq. kilometres in 2050 and 13.3m sq. kilometres in 2100. For comparability, the land space of the US is simply 9.1m sq. kilometres.

Threat evaluation

Our findings recommend there’s an pressing want to think about sustainability dangers when selecting between totally different mitigation pathways.

A method to do that could be to outline a “sustainable CDR price range”, as the quantity of CDR that could possibly be deployed sustainably throughout all CDR strategies.

Whereas our analysis solely thought of land-based CDR, different CDR choices are additionally prone to include sustainability and deployment dangers, which may restrict their potential. These embrace direct air carbon seize and storage (DACCS) or ocean-based CDR.

An alternative choice could be for scientists to establish Paris-aligned eventualities that don’t overstep sustainability limits. Our analysis means that this could possibly be a key precedence for the IPCC’s seventh evaluation cycle, in addition to integrating environmental dangers and feasibility all through the IPCC’s work.

Furthermore, our findings recommend that delaying fossil gasoline cuts, within the hope that emissions will be drawn down later this century utilizing CDR, would include excessive sustainability dangers.

If, however, nations want to account for biodiversity concerns alongside local weather objectives, whereas nonetheless limiting temperatures to 1.5C, then they would wish to observe a mitigation pathway with extra speedy cuts in fossil gasoline use, our analysis suggests.

Many of those pathways embrace behaviour adjustments and reductions in vitality demand.

International locations may take up our findings of their subsequent nationally-determined contributions (NDCs) below the Paris Settlement, due in 2025. For instance, they might tackle sustainability dangers by setting separate, clear targets for CDR, along with headline emissions objectives.

They might additionally intention to restrict their reliance on CDR – and its corresponding land footprint – with the intention to keep away from local weather actions which have unfavorable penalties for his or her nationwide biodiversity plans below the worldwide biodiversity framework (NBSAPs).