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It is still possible to comply with the Paris Climate Agreement to maintain a global temperature ‘well below +2.0 °C’ above pre-industrial levels. We present two global non-overshoot pathways (+2.0 °C and +1.5 °C) with regional decarbonization targets for the four primary energy sectors—power, heating, transportation, and industry—in 5-year steps to 2050. We use normative scenarios to illustrate the effects of efficiency measures and renewable energy use, describe the roles of increased electrification of the final energy demand and synthetic fuels, and quantify the resulting electricity load increases for 72 sub-regions. Non-energy scenarios include a phase-out of net emissions from agriculture, forestry, and other land uses, reductions in non-carbon greenhouse gases, and land restoration to scale up atmospheric CO2 removal, estimated at −377 Gt CO2 to 2100. An estimate of the COVID-19 effects on the global energy demand is included and a sensitivity analysis describes the impacts if implementation is delayed by 5, 7, or 10 years, which would significantly reduce the likelihood of achieving the 1.5 °C goal. The analysis applies a model network consisting of energy system, power system, transport, land-use, and climate models.

Peatlands cover only about 3% the global land area, but store about twice as much carbon as global forest biomass. If intact peatlands are drained for agriculture or other human uses, peat oxidation can result in considerable CO2 emissions and other greenhouse gases (GHG) for decades or even centuries. Despite their importance, emissions from degraded peatlands have so far not been included explicitly in mitigation pathways compatible with the Paris Agreement. Such pathways include land-demanding mitigation options like bioenergy or afforestation with substantial consequences for the land system. Therefore, besides GHG emissions owing to the historic conversion of intact peatlands, the increased demand for land in current mitigation pathways could result in drainage of presently intact peatlands, e.g. for bioenergy production. Here, we present the first quantitative model-based projections of future peatland dynamics and associated GHG emissions in the context of a 2 °C mitigation pathway. Our spatially explicit land-use modelling approach with global coverage simultaneously accounts for future food demand, based on population and income projections, and land-based mitigation measures. Without dedicated peatland policy and even in the case of peatland protection, our results indicate that the land system would remain a net source of CO2 throughout the 21st century. This result is in contrast to the outcome of current mitigation pathways, in which the land system turns into a net carbon sink by 2100. However, our results indicate that it is possible to reconcile land use and GHG emissions in mitigation pathways through a peatland protection and restoration policy. According to our results, the land system would turn into a global net carbon sink by 2100, as projected by current mitigation pathways, if about 60% of present-day degraded peatlands would be rewetted in the coming decades, next to the protection of intact peatlands.

Carbon dioxide removal (CDR) is crucial to achieve the Paris Agreement’s 1.5 °C–2 °C goals. However, climate mitigation scenarios have primarily focused on bioenergy with carbon capture and storage (BECCS), afforestation/reforestation, and recently direct air carbon capture and storage (DACCS). This narrow focus exposes future climate change mitigation strategies to technological, institutional, and ecological pressures by overlooking the variety of existing CDR options, each with distinct characteristics—including, but not limited to, mitigation potential, cost, co-benefits, and adverse side-effects. This study expands the scope by evaluating CDR portfolios, consisting of any single CDR approach—BECCS, afforestation/reforestation, DACCS, biochar, and enhanced weathering—or a combination of them. We analyse the value of deploying these CDR portfolios to meet 1.5 °C goals, as well as their global and regional implications for land, energy, and policy costs. We find that diversifying CDR approaches is the most cost-effective net-zero strategy. Without the overreliance on any single approach, land and energy impacts are reduced and redistributed. A diversified CDR portfolio thus exhibits lower negative side-effects, but still poses challenges related to environmental impacts, logistics or accountability. We also investigate a CDR portfolio designed to support more scalable and sustainable climate mitigation strategies, and identify trade-offs between reduced economic benefits and lower environmental impacts. Rather than a one-size-fits-all scaling down, the CDR portfolio undergoes strategic realignment, with regional customization based on techno-economic factors and bio-geophysical characteristics. Moreover, we highlight the importance of nature-based removals, especially in Brazil, Latin America, and Africa, where potentials for avoided deforestation are the greatest, emphasizing their substantial benefits, not only for carbon sequestration, but also for preserving planetary well-being and human health. Finally, this study reveals that incentivizing timely and large-scale CDR deployment by policy and financial incentives could reduce the risk of deterring climate change mitigation, notably by minimizing carbon prices.

Given their historic emissions and economic capability, we analyze a leadership role for representative industrialized regions (EU, US, Japan, and Australia) in the global climate mitigation effort. Using the global integrated assessment model REMIND, we systematically compare region-specific mitigation strategies and challenges of reaching domestic net-zero carbon emissions in 2050. Embarking from different emission profiles and trends, we find that all of the regions have technological options and mitigation strategies to reach carbon neutrality by 2050. Regional characteristics are mostly related to different land availability, population density and population trends: While Japan is resource limited with respect to onshore wind and solar power and has constrained options for carbon dioxide removal (CDR), their declining population significantly decreases future energy demand. In contrast, Australia and the US benefit from abundant renewable resources, but face challenges to curb industry and transport emissions given increasing populations and high per-capita energy use. In the EU, lack of social acceptance or EU-wide cooperation might endanger the ongoing transition to a renewable-based power system. CDR technologies are necessary for all regions, as residual emissions cannot be fully avoided by 2050. For Australia and the US, in particular, CDR could reduce the required transition pace, depth and costs. At the same time, this creates the risk of a carbon lock-in, if decarbonization ambition is scaled down in anticipation of CDR technologies that fail to deliver. Our results suggest that industrialized economies can benefit from cooperation based on common themes and complementary strengths. This may include trade of electricity-based fuels and materials as well as the exchange of regional experience on technology scale-up and policy implementation.

We explore the feasibility of limiting global warming to 1.5°C without overshoot and without the deployment of carbon dioxide removal (CDR) technologies. For this purpose, we perform a sensitivity analysis of four generic emissions reduction measures to identify a lower bound on future CO2 emissions from fossil fuel combustion and industrial processes. Final energy demand reductions and electrification of energy end uses as well as decarbonization of electricity and non-electric energy supply are all considered. We find the lower bound of cumulative fossil fuel and industry CO2 emissions to be 570 GtCO2 for the period 2016-2100, around 250 GtCO2 lower than the lower end of available 1.5°C mitigation pathways generated with integrated assessment models. Estimates of 1.5°C-consistent CO2 budgets are highly uncertain and range between 100 and 900 GtCO2 from 2016 onwards. Based on our sensitivity analysis, limiting warming to 1.5°C will require CDR or terrestrial net carbon uptake if 1.5°C-consistent budgets are smaller than 650 GtCO2. The earlier CDR is deployed, the more it neutralizes post-2020 emissions rather than producing net negative emissions. Nevertheless, if the 1.5°C budget is smaller than 550 GtCO2, temporary overshoot of the 1.5°C limit becomes unavoidable if CDR cannot be ramped up faster than to 4 GtCO2 in 2040 and 10 GtCO2 in 2050. This article is part of the theme issue 'The Paris Agreement: understanding the physical and social challenges for a warming world of 1.5°C above pre-industrial levels'.

Mitigation scenarios to limit global warming to 1.5 °C or less in 2100 often rely on large amounts of carbon dioxide removal (CDR), which carry significant potential social, environmental, political and economic risks. A precautionary approach to scenario creation is therefore indicated. This letter presents the results of such a precautionary modelling exercise in which the models C-ROADS and En-ROADS were used to generate a series of 1.5 °C mitigation scenarios that apply increasingly stringent constraints on the scale and type of CDR available. This allows us to explore the trade-offs between near-term stringency of emission reductions and assumptions about future availability of CDR. In particular, we find that regardless of CDR assumptions, near-term ambition increase ('ratcheting') is required for any 1.5 °C pathway, making this letter timely for the facilitative, or Talanoa, dialogue to be conducted by the UNFCCC in 2018. By highlighting the difference between net and gross reduction rates, often obscured in scenarios, we find that mid-term gross CO2 emission reduction rates in scenarios with CDR constraints increase to levels without historical precedence. This in turn highlights, in addition to the need to substantially increase CO2 reduction rates, the need to improve emission reductions for non-CO2 greenhouse gases. Further, scenarios in which all or part of the CDR is implemented as non-permanent storage exhibit storage loss emissions, which partly offset CDR, highlighting the importance of differentiating between net and gross CDR in scenarios. We find in some scenarios storage loss trending to similar values as gross CDR, indicating that gross CDR would have to be maintained simply to offset the storage losses of CO2 sequestered earlier, without any additional net climate benefit.

Climate policy needs to account for political and social acceptance. Current national climate policy plans proposed under the Paris Agreement lead to higher emissions until 2030 than cost-effective pathways towards the Agreements' long-term temperature goals would imply. Therefore, the current plans would require highly disruptive changes, prohibitive transition speeds, and large long-term deployment of risky mitigation measures for achieving the agreement's temperature goals after 2030. Since the prospects of introducing the cost-effective policy instrument, a global comprehensive carbon price in the near-term, are negligible, we study how a strengthening of existing plans by a global roll-out of regional policies can ease the implementation challenge of reaching the Paris temperature goals. The regional policies comprise a bundle of regulatory policies in energy supply, transport, buildings, industry, and land use and moderate, regionally differentiated carbon pricing. We find that a global roll-out of these policies could reduce global CO2 emissions by an additional 10 GtCO2eq in 2030 compared to current plans. It would lead to emissions pathways close to the levels of cost-effective likely below 2 °C scenarios until 2030, thereby reducing implementation challenges post 2030. Even though a gradual phase-in of a portfolio of regulatory policies might be less disruptive than immediate cost-effective carbon pricing, it would perform worse in other dimensions. In particular, it leads to higher economic impacts that could become major obstacles in the long-term. Hence, such policy packages should not be viewed as alternatives to carbon pricing, but rather as complements that provide entry points to achieve the Paris climate goals.

Companies are increasingly setting greenhouse gas (GHG) emission reduction targets to align with the 1.5 °C goal of the Paris Agreement. Currently, companies set these science-based targets (SBTs) for aggregate GHGs expressed in CO 2 -equivalent emissions. This approach does not specify which gases will be reduced and risk misalignment with ambitious mitigation scenarios in which individual gas emissions are mitigated at different rates. We propose that companies instead set reduction targets for separate baskets of GHGs, defined according to the atmospheric lifetimes and global mitigation potentials of GHGs. We use a sector-level analysis to approximate the average impact of this proposal on company SBTs. We apply a multiregional environmentally extended input output model and a range of 1.5 °C emissions scenarios to compare 1-, 2- and 3-basket approaches for calculating sector-level SBTs for direct (scope 1) and indirect (scope 2 and upstream scope 3) emissions for all major global sectors. The multi-basket approaches lead to higher reduction requirements for scope 1 and 2 emissions than the current single-basket approach for most sectors, because these emission sources are usually dominated by CO 2 , which is typically mitigated faster than other gases in 1.5 °C scenarios. Exceptions are scope 1 emissions for fossil and biological raw material production and waste management, which are dominated by other GHGs (mainly CH 4 and N 2 O). On the other hand, upstream scope 3 reduction targets at the sector level often become less ambitious with a multi-basket approach, owing mainly to substantial shares of CH 4 and, in some cases, non-CO 2 long-lived emissions. Our results indicate that a shift to a multi-basket approach would improve the alignment of SBTs with the Paris temperature goal and would require most of the current set of companies with approved SBTs to increase the ambition of their scope 1 and scope 2 targets. More research on the implications of a multi-basket approach on company-level SBTs for all scope 3 activities (downstream, as well as upstream) is needed.

Consumption-based carbon footprints have been widely used to examine how different demand-side solutions can reduce the emissions from personal consumption. This study not only utilized consumption-based carbon footprints to examine how people living in affluent nations like the Nordic countries can live 1.5 degree warming compatible lifestyles, but it also expanded on this analysis by focusing on which level of GHG intensity per monetary unit of expenditure it is possible to remain below a 1.5-degree compatible target level at different levels of consumption expenditure. To analyze the GHG intensity per monetary unit of consumption, first, the consumption-based carbon footprints from around 8,000 survey responses from the Nordic countries were calculated. Then the average carbon intensity per unit of monetary spending was calculated across the income deciles in each country and compared to target levels that align with the 1.5-degree compatible reduction pathways by 2030. Finally, the intensities for selected low-carbon consumption choices (vegan/vegetarian diet, driving an EV, renewable electricity for the home, not owning a car, and no air travel) were calculated and compared to the same baseline targets. Our results showed that all of the average carbon footprints and GHG intensities were above the target levels in all of the countries. However, when comparing respondents having adopted two or more low-carbon consumption choices, there were examples of average intensities that met the target levels. The adoption rates of these low-carbon consumption choices were low though, which illustrates the necessity for high adoption rates of multiple low-carbon consumption choices in order to materialize the potential of demand-side climate change mitigation options. Our findings highlight the importance of examining the GHG intensity of per monetary unit expenditure to inform future policies on demand-side solutions and to improve the climate-literacy of consumers, so they can make more informed decisions on consumption choices.

We provide the first survey of the rapidly expanding literature on country-level mitigation pathways using systematic mapping techniques. We build a database of 4691 relevant papers from the Web of Science and Scopus. We analyze their abstracts and metadata using text mining and natural language processing techniques. To discover common topics within the abstracts, we use an innovative and fully reproducible topic modeling approach based on two machine learning models. We find that the number of papers per country is well correlated with current levels of greenhouse gas (GHG) emissions, with few papers for (current) low emitters, notably in Africa. Time horizons of 2030 and 2050 each account for one-third of the papers, with the former actually more frequent in recent years, spurred by interest in the (Intended) Nationally Determined Contributions. Topic modeling analysis of the data set reveals that forward-looking mitigation papers encompass all dimensions of mitigation, save for financial issues, that are lacking. However, energy and to a lesser degree land use, land use change and forestry are very dominant relative to other sectors. Topics are unevenly addressed across countries, reflecting national circumstances and priorities, but also pointing to gaps in the literature. The limited number of forward-looking papers in (currently) low-emitting countries raises questions about the lack of research capacity in support of the construction of domestic climate policies.