“Natural” Climate Solutions Could Speed Up Mitigation, With Risks. Additional Options Are Needed.

Abstract

Mitigation of climate change by intentionally storing carbon in tropical forests, soils, and wetlands and by reducing greenhouse gas fluxes from these settings has been promoted as rapidly deployable and cost-effective. This approach, sometimes referred to as "natural climate solutions," could keep post-industrialization warming below 1.5°C, when coupled with reductions in fossil fuel emissions, as confirmed here with a simple numerical model of future emissions. However, such mitigation could cease in response to changes in future climate, land use, or natural resource policies, or there could be CO 2 released from reservoirs of stored carbon. Model simulations suggest cumulative emissions could be similar, under scenarios where carbon storage ceases, or stored carbon is released, to emissions expected in the absence of any natural mitigation. If climate change is to be minimized, no-regrets approaches to natural mitigation should be considered (e.g., by reducing deforestation), as emissions targets that could limit warming to 1.5°C cannot be met without mitigation of this magnitude. However, additional mitigation options should also be evaluated that can reduce CO 2 emissions and remove CO 2 from the air (and store it permanently).Plain Language Summary One option for fighting climate change involves "natural climate solutions" that would remove atmospheric CO 2 by storing carbon in tropical forests, soils, and wetlands and would minimize greenhouse gas fluxes from such environments. With a simple computer code to predict future emissions, I confirm that such natural mitigation could, along with reductions in fossil fuel emissions, help keep the average global post-industrialization temperature rise below 1.5°C and could help delay impacts of climate change. However, future changes in climate, land use, or natural resource policies could cause natural mitigation to cease and emissions to increase, and modeling suggests levels could approach those expected in the absence of natural mitigation, which would negate much of the intended benefit. We should prioritize "no-regrets" natural mitigation, including stopping deforestation, that can provide time to develop other needed mitigation options to remove atmospheric CO 2 and permanently store it.

Will Individual Actions Do the Trick? Comparing Climate Change Mitigation Through Geoengineering Versus Reduced Vehicle Emissions

“…This transition could follow pathways outlined in Figure 2. Once EV and geoengineering reach their maximum deployment, if all miles driven (an estimate of 1155 miles/month, per vehicle, based on data from Teter et al., 2019; EPA, 2018; OICA, 2019) are replaced with electricity‐fueled miles, the reduction in CO 2 emissions ranges from 23% (for coal‐generated electricity; van Vliet et al., 2011) to 30% (for renewable energy; van Vliet et al., 2011) of the amount of CO 2 removed from the atmosphere by afforestation/reforestation (Crusius, 2020; cites National Academies of Sciences, Engineering, and Medicine, 2019)—which has the highest efficacy of the geoengineering proposals considered (excluding CO 2 air capture for the period until 2050; Chen & Tavoni, 2013). However, for enhanced weathering (Strefler et al., 2018), these values range from 69% to 90%, and for biochar (Vaughan & Lenton, 2011; cites Lehmann et al., 2006), they range from 134% to 175% (indicating that, compared to biochar, individual action could actually have greater efficacy).…”

“…3083 Tg/month is the maximum rate; the average rate (over the course of global deployment, until the maximum rate is reached) is estimated to be 1,333 Tg/month (Chen & Tavoni, 2013). c A range of estimates were cited by Crusius (2020), with a maximum of 1008 Tg/month (cites National Academies of Sciences, Engineering, and Medicine, 2019) and a minimum of 43 Tg/month (cites Fuss et al, 2018). it is our intention to demonstrate the importance of individual solutions, via one example out of many, alongside other technological advancements.…”

Framing “nature‐based” solutions to climate change

“…In the NCS literature reviewed, cost‐effectiveness most often appeared in a highly quantified context (in keeping with the trend in NCS literature toward modeling analyses). For example, natural solutions in NCS literature were characterized as contributing significantly to the “cost‐effective mitigation” (defined by Griscom et al (2017) as less than $100 per metric ton of CO2 equivalent) required to limit global warming to 2°C (Crusius, 2020; Griscom et al, 2017; Griscom et al, 2020). On the NbS side, meanwhile, cost‐effectiveness was primarily referred to in definitional terms, as a critical component of what makes a nature‐based solution a nature‐based solution (DeLosRíos‐White et al, 2020; Kabisch et al, 2016; Pauleit et al, 2017).…”

“…Some of the NCS literature under review also questioned the permanence or effectiveness of these solutions due to temporal considerations. Qin et al (2021), for example, point to delayed action as a factor hindering the efficacy and uptake of NCS, while others highlighted the risks of climate change or future land disturbance causing a loss of carbon stocks (Crusius, 2020; Kalt et al, 2019). This effect was partly mirrored in the NbS literature, where several authors pointed to knowledge gaps in analyzing their efficacy or miscommunication around the applicability of particular solutions.…”

Large‐Scale Carbon Dioxide Removal to Meet the 1.5°C Limit: Key Governance Gaps, Challenges and Priority Responses

“…The establishment of distinct land sector targets within NDCs and within long‐term strategies will help clarify the planned contribution of the land sector (Fyson and Jeffery, 2019). Separate targets will also discourage the use of land sector removals to offset emissions in other sectors, in recognition that reductions are needed from all sectors to achieve the 1.5°C goal (Crusius, 2020, Kachi et al, 2019).…”