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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.

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.

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.

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.

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.

Understanding how net-zero emissions timelines affect sustainable development is essential for climate planning in Africa. We apply the Global Change Analysis Model to explore the continent’s energy–land–water systems under four scenarios: a business-as-usual (BAU) and three net-zero scenarios targeting 2050 (NZ50), 2070 (NZ70), and 2100 (NZ100). Our analysis quantifies how the pace of decarbonization influences Africa’s interconnected energy, land, and water systems. Without new climate policy (BAU), Africa’s net CO2 emissions could increase by nearly six-fold; from 1.8 GtCO2 yr−1 in 2020 to 10.4 GtCO2 yr−1 by 2100. All net-zero scenarios constrain this growth, with NZ50, NZ70, and NZ100 achieving net-zero emissions by their respective target years through deployment of multiple carbon dioxide removal approaches (e.g. BECCS). Across all scenarios, primary energy supply expands, but its composition shifts under net-zero conditions. Over 2020–2100, renewables account for an average of 49%–53% of primary energy in the net-zero cases, displacing fossil fuels. Net-zero pathways also drive land-use shifts, reducing cropland area by 29%–31% and lowering water demand for food crops by 14%–15%, while increasing water use for BECCS (∼0.9 km3 yr−1 in NZ50). These land constraints raise staple food prices, averaging $1.16 kg−1 in NZ50—about 96% above BAU—with the steepest increase in Western Africa. In terms of mitigation cost, NZ50 is the most expensive pathway ($78 tCO2−1), compared to $68 tCO2−1 in NZ100. While earlier action enables deeper emissions cuts and faster clean energy transitions, it also imposes higher economic and resource trade-offs. Delayed net-zero deadlines reduce near-term disruption but result in higher cumulative emissions. Given Africa’s development context, we argue that net-zero timelines must balance technical feasibility with economic realities and social justice.

This study aims to improve our understanding of the response of precipitation to forcings by proposing a physically-based equation that resolves simulated precipitation based on the atmospheric energy budget. The equation considers the balance between latent heat release by precipitation and the sum of the slow response by tropospheric temperature changes and the fast response by abrupt radiative forcing (RF) changes. The equation is tuned with three parameters for each climate model and then adequately reproduces time-varying precipitation. By decomposing the equation, we highlight the slow response as the largest contributor to forcing-driven responses and uncertainty sizes in simulations. The second largest one to uncertainty is the fast-RF response from aerosols or greenhouse gases (GHG), depending on the low or highest Coupled Model Intercomparison Projection 6 future scenarios. The likely range of precipitation change at specific warming levels under GHG removal (GGR) and solar radiation management (SRM) mitigation plans is evaluated by a simple model optimizing the relationship between temperature and decomposed contributions from multi-simulations under three scenarios. The results indicate that GGR has more severe effects from aerosols than GHG for a 1.5 K warming, resulting in 0.91%–1.62% increases in precipitation. In contrast, SRM pathways project much drier conditions than GGR results due to the tropospheric cooling and remaining anthropogenic radiative heating. Overall, the proposed physically-based equation, the decomposition analysis, and our simple model provide valuable insights into the uncertainties under different forcings and mitigation pathways, highlighting the importance of slow and fast responses to human-induced forcings in shaping future precipitation changes.

The United Nations Framework Convention on Climate Change agreed to “strengthen the global response to the threat of climate change, in the context of sustainable development and efforts to eradicate poverty” (UNFCCC 2015). Designing a global mitigation strategy to support this goal poses formidable challenges. For one, there are trade-offs between the economic costs and the environmental benefits of averting climate impacts. Furthermore, the coupled human-Earth systems are subject to deep and dynamic uncertainties. Previous economic analyses typically addressed either the former, introducing multiple objectives, or the latter, making mitigation actions responsive to new information. This paper aims at bridging these two separate strands of literature. We demonstrate how information feedback from observed global temperature changes can jointly improve the economic and environmental performance of mitigation strategies. We focus on strategies that maximize discounted expected utility while also minimizing warming above 2 °C, damage costs, and mitigation costs. Expanding on the Dynamic Integrated Climate-Economy (DICE) model and previous multi-objective efforts, we implement closed-loop control strategies, map the emerging trade-offs and quantify the value of the temperature information feedback under both well-characterized and deep climate uncertainties. Adaptive strategies strongly reduce high regrets, guarding against mitigation overspending for less sensitive climate futures, and excessive warming for more sensitive ones.

This article examines the choices that might be needed for India’s energy sector under alternative mitigation scenarios. The article draws on the CD-LINKS study—a collaborative EU project under which seven pathways based on different combinations of carbon budget (high and low) and policy implementation (early and late) were developed and examined. This study uses the MARKAL energy system model to develop these scenarios. The three broad strategies that emerge for India include decarbonisation of electricity, electrification of end-uses and improvement in energy efficiency. We conclude that by undertaking early action, India can potentially prevent carbon lock-in and leapfrog to renewables from coal in the power sector. However, early action scenarios exhibit higher cost than their delayed action counterparts. Several other barriers and challenges also need to be addressed in order to enable large-scale uptake of low-carbon technologies. India may need to come up with innovative mechanisms to ensure a smooth and just transition for the economy.