OECD iLibrary - Climate Tipping Points - Insights for Effective Policy Action
Doug Grandt
OECD iLibrary
Climate Tipping Points
Insights for Effective Policy Action
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It is also important to note that, if crossed, some climate tipping points would effectively reduce the remaining carbon budget for reaching temperature objectives. Indeed, loss of sea ice and ice sheets leads to a decrease of solar radiation reflection, effectively acting as an amplifier of surface temperatures (see Section 2.3.5). If these tipping points are crossed, emissions reductions would need to be even larger than previously thought to meet stated temperature targets. In addition, permafrost carbon emissions (see Section 2.3.3) have already led to lowering the estimated remaining carbon budgets for achieving the 1.5°C and 2°C objectives (Canadell et al., 2021[19]), even without having reached the threshold for an abrupt tipping point. Since most of these tipping elements are likely to be tipped already within the 1.5°C-2°C range, temperature feedback loops further stress how crucial it is to avoid or limit an overshooting 1.5°C.
Geoengineering: the potential use of Solar Radiation Modification technologies
Solar geoengineering, and in particular, Solar Radiation Modification (SRM) approaches have been proposed as a potential strategy to reduce future climate impacts, as well as reducing the risk of crossing climate system tipping points (Irvine, Sriver and Keller, 2012[97]; Curry et al., 2014[98];Heutel, Moreno-Cruz and Shayegh, 2016[99]). One well-known SRM approach consists of injecting sulphate aerosols in the stratosphere, thereby reducing the amount of solar radiation reaching the Earth’s surface. Such approaches have the potential to offset warming, even without a reduction in GHG emissions, however, their effectiveness and political feasibility of such approaches is debated (Barrett et al., 2014[100];Irvine, Schäfer and Lawrence, 2014[101]).
In particular, there are concern regarding risks associated with the use of SRM technologies. The latest IPCC report cautions that there remains little understanding of the potential of these technologies to actually reduce risk, and that they may also introduce novel risks to people and ecosystems (Pörtner et al., 2022[14]). The report highlights that SRM could result in substantial residual climate change by altering regional and global climate patterns (Ibid). In addition, because SRM does not change trends in emissions, climate impacts that are not directly related to temperature would not be avoided, such as ocean acidification under continued anthropogenic emissions. The report highlights there is high agreement in the literature that addressing climate change risks with SRM should only be a supplement to mitigation strategies, and should be used solely to reduce residual risks. The report also highlights considerable knowledge gaps, with low confidence in projected benefits of SRM as well as in risks to crop yields, economies, human health, or ecosystems. Finally, the report recognises that co-evolution of SRM governance and research provides a chance for responsibly developing SRM technologies, guarding against potential risks and harms relevant across a full range of scenarios. Other types of risks consist in the so-called “termination shock”, whereby a potential sudden stop of deployment of a particular SRM technology could lead to rapid and damaging rise in temperatures with potentially very dramatic impacts (Parker and Irvine, 2018[102]).
Despite the uncertainties and potential risks surrounding SRM, Heutel, Moreno-Cruz and Shayegh, (2016[99]) argue that, considering the risk of climate tipping points, solar geoengineering should be included as a policy option in an optimal climate policy strategy. This is because SRM approaches have the ability to reduce temperatures much faster than mitigation, and thus may reduce the risk of reaching a tipping point even if mitigation responses are insufficient (Heutel, Moreno-Cruz and Shayegh, 2016[99]). The authors, however, also argue against using such approaches after a tipping point has been reached. It has been highlighted that decision-making concerning SRM needs to take a risk-risk framework approach, where risks of SRM are analysed against other risks such as risks associated with e.g. climate change itself, emissions reductions, CDR or adaptation (Tyler Felgenhauer et al., 2022[103]) and that opportunities to increased investments in research for atmospheric climate interventions need to be rapidly ramped up (Silverlining, 2019[104])
All considered, given the limited level of research on geoengineering technologies, low confidence in their effectiveness and the considerable risks they are associated with, this report concludes that they are not today a feasible policy option for reducing the risk of crossing tipping points. Since mitigation strategies continue to face implementation challenges, in particular in terms of technological risks, scaling and costs, investments in technologies that can deliver 1.5°C through GHG mitigation need to be prioritised over more uncertain, and potentially riskier, geoengineering technologies.
The risk of climate tipping points also implies a key role for Carbon dioxide removal (CDR) technologies, as scenarios that limit warming to 1.5°C, with no or limited overshoot, all include at least some CDR. They serve three main purposes throughout the century: they help accelerating early deep emissions reductions, they balance out harder-to-abate sectors that continue to act as sources of residual emissions and they allow for reducing warming after peak temperature (Riahi et al., 2021[24]). It is important to note however that, since an overshoot could lead to the crossing of tipping points, the well-known argument that delayed emissions reductions can potentially be compensated by negative emissions during the latter part of the century is no longer valid.
CDR options in energy-system modelling pathways are mostly land-based biological CDR, including bioenergy with carbon capture and storage (BECCS), afforestation or soil-carbon sequestration and direct air CO2 capture and storage (DACCS) (M. Pathak, 2022[22]). While afforestation and soil-carbon sequestration have been practiced for decades to millennia (although not necessarily with the intention to remove carbon from the atmosphere), experience with BECCS and DACCS, whilst growing, is still limited (M. Pathak, 2022[22]). There remain today many legitimate concerns regarding BECCS, stemming primarily from its immense demand for land and resulting implications for land-use practices, trading-off available land for food production and impacting natural ecosystems and biodiversity (Creutzig et al., 2021[93]). It is argued that these risks may be best avoided by demand-side measures driving rapid decarbonisation in place of land-intensive carbon dioxide removal technologies (Creutzig et al., 2021[93]). Given that all scenarios in line with 1.5°C, with no or limited overshoot, include CDR, even when stringent demand-side measures are adopted, not employing CDR at all could result in the crossing of tipping points. The risks associated with BECCS can therefore no longer be considered in an isolated manner and need to be weighed against the risk of crossing tipping points. These potential trade-offs remain poorly understood and could greatly benefit from further research.
John Nissen
especially when it comes to catastrophes!
As stressed by climate scientists… the risk of crossing climate system tipping points has clear implications for short- and medium-term policy making. This adds to the urgency of considering climate tipping points in global economic costs estimations and economic analyses of climate change.
However, current modelling of the economic costs of climate change generally do not consider the possibility of large-scale singular events such as tipping elements. Due to this gap in current economic modelling on climate change, and exacerbated by difficulties in connecting the physical science modelling with economic models, most existing estimates of the costs of reaching tipping points are in fact conservative. Estimates of climate impact damages serve as a key input to calculations of the social cost of carbon (SCC) – i.e. the marginal cost of the impacts caused by the emission of an additional tonne of CO2, a key climate policy input which allows a comparison of the costs and benefits of mitigation efforts. Estimates of the SCC are generally acquired through Integrated Assessment Modelling (IAM), combining socio-economic, emission and climate modules. However, IAMs have received criticism for underestimating damages from climate change, including by overlooking the risk of crossing climate tipping points (Riahi, 2022).
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Douglas Grandt
On Dec 3, 2022, at 4:33 PM, John Nissen <johnnis...@gmail.com> wrote:
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