3.1 Ecosystem restoration: organize land-based CO2 removal in a synergistic way Measures for removing CO2 from the atmosphere are no substitute for a massive reduction of CO2 emissions with the aim of cutting them to zero. However, in order to reach the climate-protection goals of the Paris Agreement, such measures can hardly be avoided, although they involve considerable uncertainties depending on method, scope and implementation and can potentially increase the pressure on land. The WBGU recommends stepping up research on costs, feasibility, permanence and land-area potential, and making early use of the diverse additional benefits of low-risk ecosystem-based approaches like the restoration of degraded land. The fact that progress on decarbonizing the global economy has hitherto been slow with ongoing rises in global CO2 emissions is making it less and less likely that the Paris Agreement’s climate-protection goals can be achieved solely by avoiding future greenhouse-gas emissions. A later, permanent removal of CO2 from the atmosphere will probably be necessary. In this context, the various options for removing CO2 from the atmosphere are being discussed more and more intensively worldwide. Section 3.1.1 offers an overview of this discussion, as well as of the various methods of CO2 removal, their stage of development and potential, but also the risks their use entails for land-based ecosystems and their wider concomitant effects. Relying on the possibility of removing large quantities of CO2 from the atmosphere in the future is a risky strategy from the point of view of climate protection. Many methods of CO2 removal still lack technical maturity at the present time. The mitigating effect of CO2 removal on climate change is also generally uncertain. Furthermore, many approaches are land-based, especially those that are currently at the focus of attention such as afforestation or BECCS. They thus generate new claims on the use of land and land-based ecosystems; if applied on a correspondingly large scale, they threaten to cause major conflicts of use over land areas and ecosystems as outlined by the land-use trilemma described in Chapter 2. The consequence would be corresponding socio-economic risks and negative ecological effects, especially on forests, grasslands, wetlands or agriculturally used areas.
Against this background, Section 3.1.2 develops principles for a sustainable strategic approach to CO2 removal options in climate policy in order to address and minimize the multiple risks. Firstly, climate-policy strategies should emphasize consistent, early avoidance of emissions in order to limit as far as possible the amount of CO2 removal that will be necessary in the future. Secondly, they should focus more on close-tonature, ecosystem-based methods of CO2 removal, which not only bind CO2, but in particular promise diverse multiple benefits and synergies to mitigate the land-use trilemma. In Section 3.1.3, the WBGU takes an in-depth look at the restoration of degraded terrestrial ecosystems such as forests, grasslands and wetlands as an ecosystem-based option for CO2 removal. This is a proven, low-risk and cost-effective option for removing CO2 from the atmosphere. Restoration promises multiple benefits in relation to the land-use trilemma and beyond, but its potential for removing CO2 from the atmosphere is limited in terms of quantity and permanence of storage. At the same time, restoration is currently high on the international political agenda, as shown by the upcoming UN Decade on Ecosystem Restoration. The WBGU is therefore convinced that, in view of the current political tailwind, restoration should become a promising component of international climate and sustainability policy.
3.1.1 CO2 sinks: the starting position Scientific knowledge of the devastating consequences that unchecked climate change will have for humans and terrestrial ecosystems has been further intensified in recent years by reports from the Intergovernmental Panel on Climate Change and the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPCC, 2018, 2019a, c; IPBES, 2018a, 2019a). Even so, global CO2 emissions again reached a record high in 2019 (Peters et al., 2020; Friedlingstein et al., 2019; Jackson et al., 2019). In addition, the necessary tightening of the national climate pledges under the Paris Agreement already seemed a long way off even before the COVID-19 pandemic. Yet the international community agreed in the 2015 Paris Agreement to limit global warming to well below 2°C and pursue efforts towards limiting it to 1.5°C. If these goals are to be met, only a limited budget of a few hundred Gt CO2 will be available for CO2 emissions in the course of the 21st century. In 2018, according to the IPCC, these budgets for limiting global warming to 1.5°C amounted to 420 Gt CO2 (for a 66% probability of achieving the climate
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