1. United Nations Framework Convention on Climate Change 1–25 (United Nations, Rio de Janeiro, 1992).

2. Randalls, S. History of the 2 °C climate target. Wiley Interdiscip. Rev. Clim. Chang. 1, 598–605 (2010).

3. Knutti, R., Rogelj, J., Sedlacek, J. & Fischer, E. M. A scientific critique of the two-degree climate change target. Nat. Geosci. 9, 13–18 (2016).

4. O’Neill, B. C. et al. IPCC reasons for concern regarding climate change risks. Nat. Clim. Chang. 7, 28–37 (2017).

5. Seneviratne, S. I., Donat, M. G., Pitman, A. J., Knutti, R. & Wilby, R. L. Allowable CO 2 emissions based on regional and impact-related climate targets. Nature 529, 477–483 (2016).

6. UNFCCC Paris Agreement 1–25 (UNFCCC, Paris, 2015).

7. Schleussner, C.-F. et al. Science and policy characteristics of the Paris Agreement temperature goal. Nat. Clim. Chang. 6, 827–835 (2016).

8. Clarke, L. et al. in Climate Change 2014: Mitigation of Climate Change. Contribution of Working Group III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (eds O. Edenhofer et al.) Ch. 6, 413–510 (Cambridge Univ. Press, 2014).

9. Fisher, B. et al. in Climate Change 2007: Mitigation. Contribution of Working Group III to the Fourth Assessment Report of the Inter-governmental Panel on Climate Change (eds B. Metz et al.) Ch. 3, 169–250 (Cambridge Univ. Press, 2007).

10. Clarke, L. et al. International climate policy architectures: overview of the EMF 22 International Scenarios. Energy Econ. 31, S64–S81 (2009).

11. Kriegler, E. et al. The role of technology for achieving climate policy objectives: overview of the EMF 27 study on global technology and climate policy strategies. Clim. Change 123, 353–367 (2014).

12. IEA. World Energy Outlook 2015 (International Energy Agency, 2015).

13. van Vuuren, D. P. et al. A new scenario framework for climate change research: scenario matrix architecture. Clim. Change 122, 373–386 (2014).

14. Meinshausen, M. et al. Greenhouse-gas emission targets for limiting global warming to 2 °C. Nature 458, 1158–1162 (2009).

15. Matthews, H. D., Gillett, N. P., Stott, P. A. & Zickfeld, K. The proportionality of global warming to cumulative carbon emissions. Nature 459, 829–832 (2009).

16. Fuss, S. et al. Betting on negative emissions. Nat. Clim. Chang. 4, 850–853 (2014).

17. Shue, H. Climate dreaming: negative emissions, risk transfer, and irreversibility. J. Hum. Rights Environ. 8, 203–216 (2017).

18. Williamson, P. Emissions reduction: scrutinize CO 2 removal methods. Nature 530, 153–155 (2016).

19. Azar, C., Johansson, D. J. A. & Mattsson, N. Meeting global temperature targets—the role of bioenergy with carbon capture and storage. Environ. Res. Lett. 8, 034004 (2013).

20. Minx, J. C., Lamb, W. F., Callaghan, M. W., Bornmann, L. & Fuss, S. Fast growing research on negative emissions. Environ. Res. Lett. 12, 035007 (2017).

21. Smith, P. et al. Biophysical and economic limits to negative CO2 emissions. Nat. Clim. Chang. 6, 42–50 (2016).

22. Popp, A. et al. Land-use futures in the shared socio-economic pathways. Glob. Environ. Change 42, 331–345 (2017).

23. Field, C. B. & Mach, K. J. Rightsizing carbon dioxide removal. Science 356, 706–707 (2017).

24. Boysen, L. R. et al. The limits to global-warming mitigation by terrestrial carbon removal. Earths Futur. 5, 463–474 (2017).

25. Morrow, D. R. & Svoboda, T. Geoengineering and Non-Ideal Theory. Public Aff. Q. 30, 85–104 (2016).

26. Obersteiner, M. et al. How to spend a dwindling greenhouse gas budget. Nat. Clim. Chang. 8, 7–10 (2018).

27. Anderson, K. & Peters, G. The trouble with negative emissions. Science 354, 182–183 (2016).

28. Huppmann, D., Rogelj, J., Kriegler, E., Krey, V. & Riahi, K. A new scenario resource for integrated 1.5 °C research. Nat. Clim. Chang. 8, 1027–1030 (2018).

29. Rogelj, J. et al. in Global Warming of 1.5 °C: An IPCC Special Report on the Impacts of Global Warming of 1.5 °C Above Pre-industrial Levels and Related Global Greenhouse Gas Emission Pathways, in the Context of Strengthening the Global Response to the Threat of Climate Change, Sustainable Development, and Efforts to Eradicate Poverty (eds Flato, G., Fuglestvedt, J., Mrabet, R. & Schaeffer, R.) Ch. 2, 93–174 (IPCC/WMO, 2018).

30. Wigley, T. M. L., Richels, R. & Edmonds, J. A. Economic and environmental choices in the stabilization of atmospheric CO 2 concentrations. Nature 379, 240–243 (1996).

31. Rogelj, J., Schleussner, C.-F. & Hare, W. Getting it right matters: temperature goal interpretations in geoscience research. Geophys. Res. Lett. 44, 10662–10665 (2017).

32. O’Neill, B. C. et al. A new scenario framework for climate change research: the concept of shared socioeconomic pathways. Clim. Change 122, 387–400 (2014).

33. Fuglestvedt, J. et al. Implications of possible interpretations of ‘greenhouse gas balance’ in the Paris Agreement. Philos. Trans. R. Soc. A https://doi.org/10.1098/rsta.2016.0445 (2018).

34. Collins, M. et al. in Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (eds. Stocker, T. F. et al.) Ch. 12, 1029–1136 (Cambridge Univ. Press, 2013).

35. Knutti, R. & Rogelj, J. The legacy of our CO 2 emissions: a clash of scientific facts, politics and ethics. Clim. Change 133, 361–373 (2015).

36. Matthews, H. D., Solomon, S. & Pierrehumbert, R. Cumulative carbon as a policy framework for achieving climate stabilization. Philos. Trans. R. Soc. Lond. A 370, 4365–4379 (2012).

37. Matthews, H. D. & Solomon, S. Atmosphere. Irreversible does not mean unavoidable. Science 340, 438–439 (2013).

38. Matthews, H. D. & Caldeira, K. Stabilizing climate requires near-zero emissions. Geophys. Res. Lett. 35, (2008).

39. Haites, E., Yamin, F. & Höhne, N. Possible elements of a 2015 legal agreement on climate change. IDDRI SciencesPo Working Paper 1–24 (2013).

40. Rogelj, J. et al. Zero emission targets as long-term global goals for climate protection. Environ. Res. Lett. 10, 105007 (2015).

41. Geden, O. An actionable climate target. Nat. Geosci. 9, 340 (2016).

42. Weyant, J. P., de la Chesnaye, F. C. & Blanford, G. J. Overview of EMF-21: multigas mitigation and climate policy. Energy J. 27, 1–32 (2006).

43. Shindell, D. et al. Simultaneously mitigating near-term climate change and improving human health and food security. Science 335, 183–189 (2012).

44. Höglund-Isaksson, L. et al. Cost estimates of the Kigali Amendment to phase-down hydrofluorocarbons. Environ. Sci. Policy 75, 138–147 (2017).

45. Tokarska, K. B. & Zickfeld, K. The effectiveness of net negative carbon dioxide emissions in reversing anthropogenic climate change. Environ. Res. Lett. 10, 094013 (2015).

46. Creutzig, F. et al. Bioenergy and climate change mitigation: an assessment. Glob. Change Biol. Bioenergy 7, 916–944 (2015).

47. de Coninck, H. et al. in Global Warming of 1.5 °C: An IPCC Special Report on the Impacts of Global Warming of 1.5 °C Above Pre-industrial Levels and Related Global Greenhouse Gas Emission Pathways, in the Context of Strengthening the Global Response to the Threat of Climate Change, Sustainable Development, and Efforts to Eradicate Poverty (eds Abdulla, A., Boer, R., Howden, M. & Ürge-Vorsatz, D.) Ch. 4 (World Meteorological Organisation, 2018).

48. Sanchez, D. L. & Kammen, D. M. A commercialization strategy for carbon-negative energy. Nat. Energy 1, 15002 (2016).

49. Reiner, D. M. Learning through a portfolio of carbon capture and storage demonstration projects. Nat. Energy 1, 15011 (2016).

50. Krey, V., Luderer, G., Clarke, L. & Kriegler, E. Getting from here to there – energy technology transformation pathways in the EMF27 scenarios. Clim. Change 123, 369–382 (2014).

51. Luderer, G. et al. Residual fossil CO 2 emissions in 1.5–2 °C pathways. Nat. Clim. Chang. 8, 626–633 (2018).

52. Geden, O., Peters, G. P. & Scott, V. Targeting carbon dioxide removal in the European Union. Clim. Policy 19, 487–494 (2019).

53. Davis, S. J. et al. Net-zero emissions energy systems. Science 360, eaas9793 (2018).

54. Riahi, K. et al. The Shared Socioeconomic Pathways and their energy, land use, and greenhouse gas emissions implications: an overview. Glob. Environ. Change 42, 153–168 (2017).

55. Rogelj, J., McCollum, D. L., Reisinger, A., Meinshausen, M. & Riahi, K. Probabilistic cost estimates for climate change mitigation. Nature 493, 79–83 (2013).

56. Maier, H. R. et al. An uncertain future, deep uncertainty, scenarios, robustness and adaptation: how do they fit together? Environ. Model. Softw. 81, 154–164 (2016).

57. Ricke, K. L. & Caldeira, K. Maximum warming occurs about one decade after a carbon dioxide emission. Environ. Res. Lett. 9, 124002 (2014).

58. UNFCCC. FCCC/CP/2010/7/Add.1 Decision 1/CP.16—The Cancun Agreements: Outcome of the work of the Ad Hoc Working Group on Long-term Cooperative Action under the Convention (UNFCCC, 2010).

59. UNEP. The Emissions Gap Report 2013 p. 64 (UNEP, Nairobi, 2013).

60. UNFCCC. FCCC/CP/2015/7: Synthesis Report on the Aggregate Effect of the Intended Nationally Determined Contributions p. 66 (UNFCCC, Bonn, 2015).

61. Huppmann, D. et al. The MESSAGEix Integrated Assessment Model and the ix modeling platform (ixmp): an open framework for integrated and cross-cutting analysis of energy, climate, the environment, and sustainable development. Environ. Model. Softw. 112, 143–156 (2019).

62. Fricko, O. et al. The marker quantification of the Shared Socioeconomic Pathway 2: a middle-of-the-road scenario for the 21st century. Glob. Environ. Change 42, 251–267 (2017).

63. Krey, V. et al. MESSAGE-GLOBIOM 1.0 Documentation (International Institute for Applied Systems Analysis (IIASA), Laxenburg, 2016).

64. Meinshausen, M., Raper, S. C. B. & Wigley, T. M. L. Emulating coupled atmosphere-ocean and carbon cycle models with a simpler model, MAGICC6—Part 1: Model description and calibration. Atmos. Chem. Phys. 11, 1417–1456 (2011).

65. Schneider von Deimling, T. et al. Estimating the near-surface permafrost-carbon feedback on global warming. Biogeosciences 9, 649–665 (2012).

66. Etminan, M., Myhre, G., Highwood, E. J. & Shine, K. P. Radiative forcing of carbon dioxide, methane, and nitrous oxide: a significant revision of the methane radiative forcing. Geophysic. Res. Lett. 43, 12614–12623 (2016).

67. Schädel, C. et al. Circumpolar assessment of permafrost C quality and its vulnerability over time using long-term incubation data. Glob. Change Biol. 20, 641–652 (2014).

68. Burke, E. J. et al. Quantifying uncertainties of permafrost carbon–climate feedbacks. Biogeosciences 14, 3051–3066 (2017).

69. Rogelj, J. et al. Disentangling the effects of CO 2 and short-lived climate forcer mitigation. Proc. Natl Acad. Sci. USA 111, 16325–16330 (2014).

70. Bond, T. C. et al. Bounding the role of black carbon in the climate system: a scientific assessment. J. Geophys. Res. D Atmospheres 118, 5380–5552 (2013).

71. Rogelj, J. et al. Air-pollution emission ranges consistent with the representative concentration pathways. Nat. Clim. Chang. 4, 446–450 (2014).

72. Rao, S. et al. Future air pollution in the shared socio-economic pathways. Glob. Environ. Change 42, 346–358 (2017).

73. Rogelj, J. et al. Scenarios towards limiting global mean temperature increase below 1.5 °C. Nat. Clim. Chang. 8, 325–332 (2018).