Editing IPCC:AR6/SRCCL/Chapter-6 (section)

=== 6.4.5 Potential consequences of delayed action ===

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Delayed action, in terms of overall GHG mitigation across both land and energy sectors, as well as delayed action in implementing the specific response options outlined in this chapter, will exacerbate the existing land challenges due to the continued impacts of climate change and socio-economic and other pressures. It can decrease the potential of response options and increase the costs of deployment, and will deprive communities of immediate co-benefits, among other pressures. The major consequences of delayed action are outlined below.

'''Delayed action exposes vulnerable people to continued and increasing climate impacts:''' Slower or delayed action in implementing response options exacerbates existing inequalities and impacts. This will increase the number of people vulnerable to climate change, due to population increases and increasing climate impacts (IPCC 2018 <sup>[[#fn:r1199|1199]]</sup> ; AR 5). Future climate change will lead to exacerbation of the existing land challenges, increased pressure on agricultural livelihoods, potential for rapid land degradation, and millions more people exposed to food insecurity (Schmidhuber and Tubiello 2007 <sup>[[#fn:r1200|1200]]</sup> ) (Chapters 3, 4 and 5). Delay can also bring political risks and significant social impacts, including risks to human settlements (particularly in coastal areas), large-scale migration, and conflict (Barnett and Adger 2007 <sup>[[#fn:r1201|1201]]</sup> ; Hsiang et al. 2013 <sup>[[#fn:r1202|1202]]</sup> ). Early action reducing vulnerability and exposure can create an opportunity for a virtual circle of benefits: increased resilient livelihoods, reduced degradation of land, and improved food security (Bohle et al. 1994 <sup>[[#fn:r1203|1203]]</sup> ).

'''Delayed action increases requirements for adaptation:''' Failure to mitigate climate change will increase requirements for adaptation. For example, it is likely that by 2100 with no mitigation or adaptation, 31 '''–''' 69 million people world-wide could be exposed to flooding (Rasmussen et al. 2017 <sup>[[#fn:r1204|1204]]</sup> ; IPCC SR15) (Chapter 3); such outcomes could be prevented with investments in both mitigation and adaptation now. Some specific response options (e.g., reduced deforestation and forest degradation, reduced peatland and wetland conversion) prevent further detrimental effects to the land surface; delaying these options could lead to increased deforestation, conversion, or degradation, serving as increased sources of GHGs and having concomitant negative impacts on biodiversity and ecosystem services (Section 6.2). Response options aimed at land restoration and rehabilitation can serve as adaptation mechanisms for communities facing climatic stresses like precipitation variability and changes in land quality, as well as provide benefits in terms of mitigation.

'''Delayed action increases response costs and reduces economic growth:''' Early action on reducing emissions through mitigation is estimated to result in smaller temperature increases as well as lower mitigation costs than delayed action (Sanderson et al. 2016 <sup>[[#fn:r1205|1205]]</sup> ; Luderer et al. 2013, 2018; Rose et al. 2017 <sup>[[#fn:r1206|1206]]</sup> ; Van Soest et al. 2017; Fujimori et al. 2017 <sup>[[#fn:r1207|1207]]</sup> ). The cost of inaction to address mitigation, adaptation, and sustainable land use exceeds the cost of immediate action in most countries, depending on how damage functions and the social cost of carbon are calculated (Dell et al. 2012 <sup>[[#fn:r1208|1208]]</sup> ; Moore and Diaz 2015 <sup>[[#fn:r1209|1209]]</sup> ). Costs of acting now would be one to two orders of magnitude lower than economic damages from delayed action, including damage to assets from climate impacts, as well as potentially reduced economic growth, particularly in developing countries (Luderer et al. 2016 <sup>[[#fn:r1210|1210]]</sup> ; Moore and Diaz 2015 <sup>[[#fn:r1211|1211]]</sup> ; Luderer et al. 2013 <sup>[[#fn:r1212|1212]]</sup> ). Increased health costs and costs of energy (e.g., to run air-conditioners to combat increased heat waves) in the US by the end of the century alone are estimated to range from 10–58% of US GDP in 2010 (Deschênes and Greenstone 2011).

Delay also increases the costs of both mitigation and adaptation actions at later dates. In models of climate-economic interactions, deferral of emissions reduction now requires trade-offs leading to higher costs of several orders of magnitude and risks of higher temperatures in the longer term (Luderer et al. 2013 <sup>[[#fn:r1213|1213]]</sup> ). Further, the cost of action is likely to increase over time due to the increased severity of challenges in future scenarios.

Conversely, timely implementation of response options brings economic benefits. Carbon pricing is one economic component to encourage adoption of response options (Jakob et al. 2016 <sup>[[#fn:r1214|1214]]</sup> ), but carbon pricing alone can induce higher risk in comparison to other scenarios and pathways that include additional targeted sustainability measures, such as promotion of less material- and energy-intensive lifestyles and healthier diets, as noted in our response options (Bertram et al. 2018 <sup>[[#fn:r1215|1215]]</sup> ). While the short-term costs of deployment of actions may increase, better attainment of a broad set of sustainability targets can be achieved through these combined measures (Bertram et al. 2018 <sup>[[#fn:r1216|1216]]</sup> ).

There are also investments now that can lead to immediate savings in terms of avoided damages; for example, for each dollar spent on disaster risk management, countries accrue avoided disaster-related economic losses of 4 USD or more (Mechler 2016 <sup>[[#fn:r1217|1217]]</sup> ). While they can require upfront investment, the economic benefits of actions to ensure sustainable land management, such as increased soil organic carbon, can more than double the economic value of rangelands and improve crop yields (Chapter 4 and Section 6.2).

'''Delayed action reduces future policy space and decreases efficacy of some response options:''' The potential for some response options decreases as climate change increases; for example, climate alters the sink capacity for soil and vegetation carbon sequestration, reducing the potential for increased soil organic carbon, afforestation and reforestation (Section 6.4.2). Additionally, climate change affects the productivity of bioenergy crops, influencing the potential mitigation of bioenergy and BECCS (Section 6.4.4).

For response options in the supply chain, demand-side management, and risk management, while the consequences of delayed action are apparent in terms of continued GHG emissions from drivers, the tools for response options are not made more difficult by delay and could be deployed at any time. Additionally, given increasing pressures on land as a consequence of delay, some policy response options may become more cost-effective while others become costlier. For example, over time, land-based mitigation measures like forest and ecosystem protection are likely to increase land scarcity, leading to higher food prices; while demand-side measures, like reduced-impact diets and reducing waste, are less likely to raise food prices in economic models (Stevanović et al. 2017 <sup>[[#fn:r1218|1218]]</sup> ).

For risk management, some response options provide timely and rapidly deployable solutions for preventing further problems, such as disaster risk management and risk-sharing instruments. For example, early warning systems serve multiple roles in protecting lives and property and helping people adapt to longer-term climate changes, and can be used immediately.

'''Delaying action can also result in problems of irreversibility of biophysical impacts and tipping points:''' Early action provides a potential way to avoid irreversibility – such as degradation of ecosystems that cannot be restored to their original baseline – and tipping points, whereby ecological or climate systems abruptly shift to a new state. Ecosystems, such as peatlands, are particularly vulnerable to irreversibility because of the difficulties of rewetting to original states (Section 6.2), and dryland grazing systems are vulnerable to tipping points when ground cover falls below 50%, after which productivity falls, infiltration declines, and erosion increases (Chapters 3 and 4). Further, tipping points can be especially challenging for human populations to adapt to, given the lack of prior experience with such system shifts (Kates et al. 2012 <sup>[[#fn:r1219|1219]]</sup> ; Nuttall 2012 <sup>[[#fn:r1220|1220]]</sup> ).

'''Policy responses require lead time for implementation; delay makes this worse:''' For all the response options, particularly those that need to be deployed through policy implementation, there are unavoidable lags in this cycle. ‘Policy lags’, by which implementation is delayed by the slowness of the policy implementation cycle, are significant across many land-based, response options (Brown et al. 2019 <sup>[[#fn:r1221|1221]]</sup> ). Further, the behavioural change necessary to achieve some demand-side and risk management response options often takes a long time, and delay only lengthens this process (Stern 1992 <sup>[[#fn:r1222|1222]]</sup> ; Steg and Vlek 2009 <sup>[[#fn:r1223|1223]]</sup> ). For example, actively promoting the need for healthier and more sustainable diets through individual dietary decisions is an important underpinning and enabling step for future changes, but is likely to be a slow-moving process, and delay in beginning will only exacerbate this.

'''Delay can lead to lock-in:''' Delay in implementation can cause ‘lock-in’ as decisions made today can constrain future development and pathways. For example, decisions made now on where to build infrastructure, make investments and deploy technologies, will have longer-term (decades-long) ramifications due to the inertia of capital stocks (Van Soest et al. 2017). In tandem, the vulnerability of the poor is likely to be exacerbated by climate change, creating a vicious circle of lock in whereby an increasing share of the dwindling carbon budget may be needed to assist with improved energy use for the poorest (Lamb and Rao 2015 <sup>[[#fn:r1224|1224]]</sup> ).

'''Delay can increase the need for widespread deployment of land-based mitigation (afforestation, BECCS)''' (IPCC 2018 <sup>[[#fn:r1225|1225]]</sup> ; Strefler et al. 2018 <sup>[[#fn:r1226|1226]]</sup> ): Further delays in mitigation could result in an increased need for carbon dioxide removal (CDR) options later; for example, delayed mitigation requires a 10% increase in cumulative CDR over the century (IPCC 2018 <sup>[[#fn:r1227|1227]]</sup> ). Similarly, strengthening near-term mitigation effort can reduce the CDR requirements in 2100 by a factor of 2 to 8 (Strefler et al. 2018 <sup>[[#fn:r1228|1228]]</sup> ). Conversely, scenarios with limited CDR require earlier emissions reductions (Van Vuuren et al. 2017b) and may make more stringent mitigation scenarios, like the 1.5°C, infeasible (Kriegler et al. 2018a,b).

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