Many countries have implemented national climate policies to accomplish pledged Nationally Determined Contributions and to contribute to the temperature objectives of the Paris Agreement on climate change. In 2023, the global stocktake will assess the combined effort of countries. Here, based on a public policy database and a multi-model scenario analysis, we show that implementation of current policies leaves a median emission gap of 22.4 to 28.2 GtCO2eq by 2030 with the optimal pathways to implement the well below 2 °C and 1.5 °C Paris goals. If Nationally Determined Contributions would be fully implemented, this gap would be reduced by a third. Interestingly, the countries evaluated were found to not achieve their pledged contributions with implemented policies (implementation gap), or to have an ambition gap with optimal pathways towards well below 2 °C. This shows that all countries would need to accelerate the implementation of policies for renewable technologies, while efficiency improvements are especially important in emerging countries and fossil-fuel-dependent countries. To evaluate the effectiveness of current national policies in achieving global temperature targets is important but a systematic multi-model evaluation is still lacking. Here the authors identified a reduction of 3.5 GtCO2 eq of current national policies relative to a baseline scenario without climate policies by 2030 due to the increasing low carbon share of final energy and the improving final energy intensity.
This data set includes global climate change mitigation scenarios as summarized by Riahi et al., 2021. The scenarios are developed as part of the ENGAGE project and were assessed in terms of the their investment implications (Bertram et al., 2021), their land-use dynamics (Hasegawa et al., 2021) as we all as with respect to their costs and benefits (Drouret et al., 2021). The scenarios include a current national policies scenario and an NDC scenario that depict relevant near-term GHG emission tends and targets. In the long-term, two types of CO2 emission budgets are implemented, so called “net-zero budgets” and “end-of-century” budgets. The “net-zero-budget”scenarios assume climate policies that limit the remaining cumulative CO2 emissions until net zero CO2 emissions are reached. These scenarios limit the temperature overshoot and do not rely on global net-negative CO2 emissions to keep warming below the intended temperature limit. In contrast, the “end-of-century budget”scenarios assume long-term climate policies that limit cumulative CO2 emissions over the full course of the 21st century. Depending on the availability of carbon dioxide removal options, these scenarios may comprise high temperature overshoot and global net negative CO2 emissions in the second half of the century. The near-term dimension of current national policies until 2020 or NDCs until 2030 is then combined with reaching the net-zero and full-century CO2 emissions budgets. To cover a relevant range of temperature outcomes (which in addition to the budgets themselves also determined by mitigation of non-CO2 GHG and aerosol emissions), the budgets are varied between 200 and 3000 GtCO2 in steps of 50 – 500 GtCO2. The data is available for download at the ENGAGE Scenario Explorer. The license permits use of the scenario ensemble for scientific research and science communication, but restricts redistribution of substantial parts of the data. Please refer to the FAQ and legal code for more information.
Abstract Despite its projected crucial role in stringent, future global climate policy, non-CO 2 greenhouse gas (NCGG) mitigation remains a large uncertain factor that has received relatively little scientific attention. A revision of the estimated mitigation potential could have massive implications for the feasibility of global climate policy to reach the Paris Agreement climate goals. Here, we provide a systematic bottom-up estimate of the total uncertainty in NCGG mitigation, by developing “optimistic, default and pessimistic” long-term non-CO 2 marginal abatement cost (MAC) curves. The global 1.5-degree climate target is found to be out of reach under pessimistic MAC assumptions, as is the 2-degree target under high emission assumptions. MAC uncertainty translates into a large projected range in (all in a 2-degree scenario) relative NCGG reduction (40–58%), carbon budget (± 120 Gt CO 2 ) and policy costs (± 16%). Partly, the MAC uncertainty signifies a gap that could be bridged by human efforts, but largely it indicates uncertainty in technical limitations.
Abstract This study examines model-specific assumptions and projections of methane (CH 4 ) emissions in deep mitigation scenarios generated by integrated assessment models (IAMs). For this, scenarios of nine models are compared in terms of sectoral and regional CH 4 emission reduction strategies, as well as resulting climate impacts. The models’ projected reduction potentials are compared to sector and technology-specific reduction potentials found in literature. Significant cost-effective and non-climate policy related reductions are projected in the reference case (10–36% compared to a “frozen emission factor” scenario in 2100). Still, compared to 2010, CH 4 emissions are expected to rise steadily by 9–72% (up to 412 to 654 Mt CH 4 /year). Ambitious CO 2 reduction measures could by themselves lead to a reduction of CH 4 emissions due to a reduction of fossil fuels (22–48% compared to the reference case in 2100). However, direct CH 4 mitigation is crucial and more effective in bringing down CH 4 (50–74% compared to the reference case). Given the limited reduction potential, agriculture CH 4 emissions are projected to constitute an increasingly larger share of total anthropogenic CH 4 emissions in mitigation scenarios. Enteric fermentation in ruminants is in that respect by far the largest mitigation bottleneck later in the century with a projected 40–78% of total remaining CH 4 emissions in 2100 in a strong (2 °C) climate policy case.
Change in the air The 2016 Paris Agreement set the ambitious goals of keeping global temperature rise this century below 2°C, or even better, 1.5°C above preindustrial levels. Substantial interventions are required to meet these goals, particularly for industrialized countries. Duan et al. projected that China will need to reduce its carbon emissions by more than 90% and its energy consumption by almost 40% to do its share in reaching the 1.5°C target. Negative emission technology is an essential element of any plan. China's accumulated economic costs by 2050 may be about 3 to 6% of its gross domestic product. Science , this issue p. 378
This study designed and tested (by means of a case study) an improved method for systematically reviewing (scientific) literature. The case study focused on the use of information and communication technology (ICT) in the field of human development. Findings with regard to ICT use indicate a potential 'digital divide' as ICT users were generally found to be (somewhat) better educated, younger and wealthier than non-users. With regard to effects of ICT use, broad evidence suggests that ICT use is associated with higher income. Effects in studies with a more specific focus were found to concentrate on market improvements, among others by better integration, elimination of waste, and better negotion options for farmers. Findings regarding the method used indicate that it allows for a more systematic and transparent determination of focus, and subsequently integration of findings in complex domains.
Emissions of air pollutants such as sulfur and nitrogen oxides and particulates have significant health impacts as well as effects on natural and anthropogenic ecosystems. These same emissions also can change atmospheric chemistry and the planetary energy balance, thereby impacting global and regional climate. Long-term scenarios for air pollutant emissions are needed as inputs to global climate and chemistry models, and for analysis linking air pollutant impacts across sectors. In this paper we present methodology and results for air pollutant emissions in Shared Socioeconomic Pathways (SSP) scenarios. We first present a set of three air pollution narratives that describe high, central, and low pollution control ambitions over the 21st century. These narratives are then translated into quantitative guidance for use in integrated assessment models. The resulting pollutant emission trajectories under the SSP scenarios cover a wider range than the scenarios used in previous international climate model comparisons. In the SSP3 and SSP4 scenarios, where economic, institutional and technological limitations slow air quality improvements, global pollutant emissions over the 21st century can be comparable to current levels. Pollutant emissions in the SSP1 scenarios fall to low levels due to the assumption of technological advances and successful global action to control emissions.
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