ALBERT

Description: While the Intergovernmental Panel on Climate Change (IPCC) physical science reports usually assess a handful of future scenarios, the Working Group III contribution on climate mitigation to the IPCC's Sixth Assessment Report (AR6 WGIII) assesses hundreds to thousands of future emissions scenarios. A key task in WGIII is to assess the global mean temperature outcomes of these scenarios in a consistent manner, given the challenge that the emissions scenarios from different integrated assessment models (IAMs) come with different sectoral and gas-to-gas coverage and cannot all be assessed consistently by complex Earth system models. In this work, we describe the “climate-assessment” workflow and its methods, including infilling of missing emissions and emissions harmonisation as applied to 1202 mitigation scenarios in AR6 WGIII. We evaluate the global mean temperature projections and effective radiative forcing (ERF) characteristics of climate emulators FaIRv1.6.2 and MAGICCv7.5.3 and use the CICERO simple climate model (CICERO-SCM) for sensitivity analysis. We discuss the implied overshoot severity of the mitigation pathways using overshoot degree years and look at emissions and temperature characteristics of scenarios compatible with one possible interpretation of the Paris Agreement. We find that the lowest class of emissions scenarios that limit global warming to “1.5 ∘C (with a probability of greater than 50 %) with no or limited overshoot” includes 97 scenarios for MAGICCv7.5.3 and 203 for FaIRv1.6.2. For the MAGICCv7.5.3 results, “limited overshoot” typically implies exceedance of median temperature projections of up to about 0.1 ∘C for up to a few decades before returning to below 1.5 ∘C by or before the year 2100. For more than half of the scenarios in this category that comply with three criteria for being “Paris-compatible”, including net-zero or net-negative greenhouse gas (GHG) emissions, median temperatures decline by about 0.3–0.4 ∘C after peaking at 1.5–1.6 ∘C in 2035–2055. We compare the methods applied in AR6 with the methods used for SR1.5 and discuss their implications. This article also introduces a “climate-assessment” Python package which allows for fully reproducing the IPCC AR6 WGIII temperature assessment. This work provides a community tool for assessing the temperature outcomes of emissions pathways and provides a basis for further work such as extending the workflow to include downscaling of climate characteristics to a regional level and calculating impacts.

Description: This document provides technical information on the two datasets behind the NGFS scenarios. It is intended to answer technical questions for those who want to perform analyses on the datasets themselves. It is an update of the Technical Documentations published in June 2020 and 2021 alongside the first two sets of NGFS Scenarios. It is therefore aligned with the third set of NGFS Scenarios, released in September 2022.

Description: Chapter 3 takes a long-term perspective on climate change mitigation pathways. Its focus is on the implications of long-term targets for the required short- and medium-term system changes and associated greenhouse gas (GHG) emissions. This focus dictates a more global view and on issues related to path-dependency and up-scaling of mitigation options necessary to achieve different emissions trajectories, including particularly deep mitigation pathways that require rapid and fundamental changes.

Description: The use of scenarios and modelling methods are pillars in IPCC Working Group III (WGIII) Assessment Reports. Past WGIII assessment report cycles identified knowledge gaps about the integration of modelling across scales and disciplines, mainly between global integrated assessment modelling methods and bottom-up modelling insights of mitigation responses. The need to improve the transparency of model assumptions and enhance the communication of scenario results was also recognised. This annex on Scenarios and Modelling Methods aims to address some of these gaps by detailing the modelling frameworks applied in the WGIII Sixth Assessment Report (AR6) chapters and disclose scenario assumptions and its key parameters. It has been explicitly included in the Scoping Meeting Report of the WGIII contribution to the AR6 and approved by the IPCC Panel at the 46th Session of the Panel. The annex includes two parts: Part I on Modelling Methods summarises methods and tools available to evaluate sectoral, technological and behavioural mitigation responses as well as integrated assessment models (IAMs) for the analysis of ‘whole system’ transformation pathways; Part II on Scenarios sets out the portfolio of climate change scenarios and mitigation pathways assessed in the AR6 WGIII chapters, its underlying principles and interactions with scenario assessments by WGI and WGII.

Description: The European Climate Law (2021) legislated the targets set out in the European Green Deal of climate neutrality (net-zero GHGs) by 2050 and an intermediate target of 55% reduction by 2030 compared to 1990. Established as part of the European Climate Law in 2021, the European Scientific Advisory Board on Climate Change (Advisory Board), has been tasked with advising the EU on a subsequent intermediate target for 2040, and indicative budgets for EU greenhouse gas emissions for the 2030-2050 period. This advice should also be in line with other international commitments such as the Paris Agreement. In 2022, via a Call for Scenarios, the Advisory Board invited the wider research community to submit emissions scenario data to support the evidence base for its advice. More than 1100 scenarios were collected and assessed in an emissions scenario database hosted online by IIASA, with thirty additional scenarios from the Potsdam Institute for Climate Impact Research (PIK) to further assist the analysis. This report, and supporting data and code, aims to transparently document the additional scenario data processing and analysis that has been undertaken to assist the Advisory Board’s deliberations. Much of the assessment presented here builds on best-practice methods recently used in the IPCC’s latest report, the 6th Assessment Report (AR6).