28 Jun 2022
28 Jun 2022
Status: this preprint is open for discussion.

The IPCC Sixth Assessment Report WGIII climate assessment of mitigation pathways: from emissions to global temperatures

Jarmo S. Kikstra1,2,3, Zebedee R. J. Nicholls1,4,5, Christopher J. Smith1,6, Jared Lewis1,4,5, Robin D. Lamboll2,3, Edward Byers1, Marit Sandstad7, Malte Meinshausen4,5, Matthew J. Gidden1,8, Joeri Rogelj1,2,3, Elmar Kriegler9,10, Glen P. Peters7, Jan S. Fuglestvedt7, Ragnhild B. Skeie7, Bjørn H. Samset7, Laura Wienpahl1, Detlef P. van Vuuren11,12, Kaj-Ivar van der Wijst12, Alaa Al Khourdajie3, Piers M. Forster6, Andy Reisinger13, Roberto Schaeffer14, and Keywan Riahi1,15 Jarmo S. Kikstra et al.
  • 1Energy, Climate and Environment (ECE) Program, International Institute for Applied Systems Analysis (IIASA), Laxenburg, 2361, Austria
  • 2The Grantham Institute for Climate Change and the Environment, Imperial College London, London, UK
  • 3Centre for Environmental Policy, Imperial College London, London, UK
  • 4Climate & Energy College, School of Geography, Earth and Atmospheric Sciences, The University of Melbourne
  • 5Climate Resource, Melbourne, Australia
  • 6Priestley International Centre for Climate, University of Leeds, Leeds, United Kingdom
  • 7CICERO Center for International Climate Research, Oslo, Norway
  • 8Climate Analytics, Berlin, Germany
  • 9Potsdam Institute for Climate Impact Research (PIK), Potsdam, Germany
  • 10Faculty of Economics and Social Sciences, University of Potsdam, Potsdam, Germany
  • 11PBL Netherlands Environmental Assessment Agency, The Hague, The Netherlands
  • 12Copernicus Institute of Sustainable Development, Utrecht University, Utrecht, The Netherlands
  • 13Institute for Climate, Energy and Disaster Solutions, Fenner School of Society & Environment, Australian National University, Canberra, Australia
  • 14Centre for Energy and Environmental Economics (CENERGIA), COPPE, Universidade Federal do Rio de Janeiro (UFRJ), Rio de Janeiro, Brazil
  • 15Graz University of Technology, Graz, Austria

Abstract. While the IPCC’s physical science report usually assesses a handful of future scenarios, the IPCC Sixth Assessment Working Group III report (AR6 WGIII) on climate mitigation assesses hundreds to thousands of future emissions scenarios. A key task is to assess the global-mean temperature outcomes of these scenarios in a consistent manner, given the challenge that the emission scenarios from different integrated assessment models 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 1,202 mitigation scenarios in AR6 WGIII. We evaluate the global-mean temperature projections and effective radiative forcing characteristics (ERF) of climate emulators FaIRv1.6.2, MAGICCv7.5.3, and CICERO-SCM, discuss overshoot severity of the mitigation pathways using overshoot degree years, and look at an interpretation of compatibility with the Paris Agreement. We find that the lowest class of emission scenarios that limit global warming to “1.5 °C (with a probability of greater than 50 %) with no or limited overshoot” includes 90 scenarios for MAGICCv7.5.3, and 196 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 of this category that comply with three criteria for being “Paris-compatible”, including net-zero or net-negative greenhouse gas (GHG) emissions, are projected to see 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 the implications. This article also introduces a ‘climate-assessment’ Python package which allows for fully reproducing the IPCC AR6 WGIII temperature assessment. This work can be the start of a community tool for assessing the temperature outcomes related to emissions pathways, and potential further work extending the workflow from emissions to global climate by downscaling climate characteristics to a regional level and calculating impacts.

Jarmo S. Kikstra et al.

Status: open (until 23 Aug 2022)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • CC1: 'Comment on egusphere-2022-471', Richard Rosen, 09 Jul 2022 reply
  • RC1: 'Comment on egusphere-2022-471', Anonymous Referee #1, 20 Jul 2022 reply
  • RC2: 'Comment on egusphere-2022-471', Anonymous Referee #2, 03 Aug 2022 reply

Jarmo S. Kikstra et al.

Model code and software

Climate assessment of long-term emissions pathways: IPCC AR6 WGIII version Jarmo S. Kikstra, Zebedee R.J. Nicholls, Jared Lewis, Christopher J. Smith, Robin D. Lamboll, Edward Byers, Marit Sandstad, Laura Wienpahl, Philip Hackstock

Jarmo S. Kikstra et al.


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Short summary
Assessing hundreds or thousands of emission scenarios in terms of their global-mean temperature implications requires standardised procedures of infilling, harmonisation and probabilistic temperature assessments. We here present the ‘climate-assessment’ workflow that provides the methodology used in the IPCC Working Group III report.