Future Earth and World Climate Research Programme have convened a statement from scientists around the world in response to comments regarding fossil fuel phaseout pathways. This statement has been covered in the New York Times and the Guardian.

If you are a scientist working on climate change, it’s open for signature at the bottom of the statement.

The science is clear: we need net zero carbon dioxide emissions by 2050

For all intents and purposes, moving towards the phase-out of fossil fuel combustion is necessary to keep the 1.5°C goal of the Paris Agreement within reach. Deploying carbon dioxide removal (CDR) at scale, while being judicious about its limitations and trade-offs, will also be necessary to complement the phase out of fossil fuels, as there will be some residual emissions from hard-to-abate sectors.

As assessed by the IPCC, reaching net zero carbon dioxide emissions by 2050 is required to stand a chance of holding global warming to 1.5°C this century. Net zero means that all anthropogenic carbon dioxide emissions are balanced by anthropogenic carbon dioxide removals. Scenarios consistent with this goal require a complete phase-out of coal by 2050 and rapid phase-down of oil and gas (halved every decade). After 2050 the world needs to rapidly move into net negative emissions, particularly after a number of decades of 1.5°C overshoot. 

The most recent assessments of pathways to limit warming at 1.5°C show that by 2050 all unabated use of coal needs to be completely phased-out, while oil and unabated gas need to be phased down by 60-90%.1 To have a 50% chance of holding the global temperature increase to 1.5°C, we can only emit another 275 Gt of carbon dioxide.2 At current emissions rates, we will have used up this budget in just 7 years. Over its lifetime, the existing infrastructure for the extraction and use of fossil fuels would emit more than the world’s remaining carbon budget. New planned infrastructure and exploration for new fossil fuel reserves would exceed this budget many times over.3

All modelling scenarios that limit warming to 1.5°C – with or without a temporary temperature overshoot – rely on carbon dioxide removal (CDR) in order to achieve net zero emissions by 2050 and net negative emissions from 2050 onwards. Current CDR methods amount to about 5% of fossil fuel emissions and rely almost entirely on using nature to enhance carbon storage, but the permanence and scale-up potential of these nature-based CDR methods are uncertain as they are vulnerable to multiple threats including climate change (e.g. due to increases in extremes such as droughts or wildfires). There are also significant trade-offs with food and water security and the protection of biodiversity. 

Novel, technology-based, CDR methods currently provide just 0.1% of CDR from the atmosphere4 (this includes direct air capture and storage, bioenergy with carbon capture and storage). Novel CDR is just now moving from pilot experiments into its scaling phase and while theoretically promising there is no evidence yet that these methods can be deployed at the scale needed.  Nor do we know whether these CDR methods will be enough to remove even the difficult-to-abate emissions in a timely manner.  

Given the certainty about the shrinking carbon budget, and the overwhelming uncertainty about the scalability of CDR, the only certain way to curb global warming and reach net zero is to reduce fossil fuel emissions to the unavoidable minimum level – and concurrently invest in CDR to offset the remaining amount of residual fossil fuel emissions. This residual needs to be kept as low as possible in view of the uncertainties of scale, storage timescale, and trade-offs associated with CDR.  

The natural carbon sinks beyond human activity are not included in the net zero equation. The remaining carbon budget already factors in the continued performance of natural land and ocean carbon sinks to remove a significant fraction of anthropogenic emissions (also accounting for their declining efficiency in a warmer world). 

The science is clear: there is no room for ambiguity on the required action for achieving net zero carbon dioxide emissions by 2050.

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Writing team (in alphabetical order):

Wendy Broadgate, Future Earth Global Hub Director, Sweden
Pierre Friedlingstein, University of Exeter, UK
Sophie Hebden, Future Earth, Sweden and European Space Agency, UK
Daniel Ospina, Future Earth, Sweden
Julia Pongratz, Ludwig-Maximilians-Universität in Munich, Germany
Johan Rockström, PIK, Germany
Detlef Stammer, Universität Hamburg, Germany

Additional signatories:

Pep Canadell, Global Carbon Project, Future Earth
Peter Schlosser, Arizona State University, USA
Laura Pereira, Global Change Institute, University of the Witwatersrand, South Africa
Tim Lenton, University of Exeter, UK
Kristie L. Ebi, University of Washington, USA
Mercedes Bustamante, University of Brasília, Brazil
Helen Cleugh, WCRP and ANU, Australia
Carlos Nobre, University of São Paulo, Brazil
Michael Sparrow, WMO
H Damon Matthews, Concordia University, Canada
Katharine Hayhoe, Texas Tech University / The Nature Conservancy
Hans Poertner, Alfred-Wegener-Institute
Valérie Masson-Delmotte , IPSL/LSCE, Université Paris Saclay, France
Aditi Mukherji, CGIAR
Roberta Boscolo, WMO
Youba Sokona, Former IPCC Vice Chair
Jean-Pascal van Ypersele, UCLouvain (Belgium), former IPCC Vice-Chair
Pascale Braconnot, Laboratoire des sciences du climat et de l’environnement, France
Robert Vautard, Institut Pierre-Simon Laplace, France
Jean-Pierre Gattuso, CNRS-Sorbonne Université, France
Stefan Rahmstorf, Potsdam Institute for Climate Impact Research, Germany
Elmar Kriegler, Potsdam Institute for Climate Impact Research, Germany
Prabir K. Patra, JAMSTEC, Yokohama & RIHN, Kyoto, Japan.
Malte Meinshausen, University of Melbourne, Australia
Ana Bastos, Max Planck Institute for Biogeochemistry, Germany
Kirsten Zickfeld, Simon Fraser University, Canada
Nebojsa Nakicenovic. International Institute for Applied Systems Analysis, Austria
Deliang Chen, University of Gothenburg, Sweden
James W. Hurrell, Colorado State University, USA
Silvina A. Solman, University of Buenos Aires & CONICET, Argentina
Joyashree Roy, Asian Institute of Technology, Thailand and Jadavpur University, India
Veronika Eyring, Deutsches Zentrum für Luft- und Raumfahrt (DLR) & University of Bremen, Germany
Minal Pathak, Ahmedabad University, India
Markku Kulmala, University of Helsinki, Finland
Ed Hawkins, University of Reading, UK
Nicolas Gruber, ETH Zurich, Switzerland
Regina R Rodrigues, Federal University of Santa Catarina, Brazil
Ilana Wainer, University of São Paulo, Brazil
Roberto Sánchez, COLEF, Mexico
Mark Maslin, University College London, UK
Zeke Hausfather, Berkeley Earth, USA
Lisa Schipper, University of Bonn, Germany
Niklas Höhne, NewClimate Institute, Germany and Wageningen University, The Netherlands
Bill Hare, Murdoch University, Western Australia/Climate Analytics.
David Obura, Director, CORDIO East Africa
Nico Wunderling, PIK, Germany
Judith Hauck, Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany
Anja Rammig, Technical University of Munich, Germany
Marcos Fernández-Martínez, Ecological and Forestry Applications Research Centre (CREAF), Bellaterra, Spain
Julio Cesar Pedrassoli, Federal University of Bahia, Brazil
Sönke Zaehle, Max Planck Institute for Biogeochemistry, Jena, Germany,
Norman J. Steinert, NORCE Norwegian Research Centre, Bergen, Norway
Yunne Shin, Institut de Recherche pour le Développement, Montpellier, France
Thomas Frölicher, University of Bern, Switzerland
Attila Buzási, Budapest University of Technology and Economics, Hungary
Robert W. Orttung, George Washington University, USA
Jeremiás Máté Balogh, Corvinus University of Budapest, Hungary
Gregory Nemet, University of Wisconsin-Madison
Georgia Destouni, Stockholm University & KTH Royal Institute of Technology, Stockholm, Sweden

References

1 IPCC, 2023: Climate Change 2023: Synthesis Report. Contribution of Working Groups I, II and III to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Core Writing Team, H. Lee and J. Romero (eds.)]. IPCC, Geneva, Switzerland, 184 pp., https://www.ipcc.ch/report/ar6/syr/  

IEA. (2021). Net Zero by 2050—A Roadmap for the Global Energy Sector. International Energy Agency. https://www.iea.org/reports/net-zero-by-2050

IEA. (2023). Net Zero Roadmap: A Global Pathway to Keep the 1.5 °C Goal in Reach – A renewed pathway to net zero emissions. International Energy Agency. https://www.iea.org/reports/net-zero-roadmap-a-global-pathway-to-keep-the-15-0c-goal-in-reach 

2 Friedlingstein et al, Global Carbon Budget 2023, Earth Syst. Sci. Data, 15, 1–69, 2023

https://doi.org/10.5194/essd-15-5301-2023

3 IPCC AR6 Synthesis report (2023), IEA (2021, 2023), and 

UNEP (2023). Emissions Gap Report 2023: Broken Record – Temperatures hit new highs, yet world fails to cut emissions (again). Nairobi. https://doi.org/10.59117/20.500.11822/43922

SEI, Climate Analytics, E3G, IISD, and UNEP. (2023). The Production Gap: Phasing down or phasing up? Top fossil fuel producers plan even more extraction despite climate promises. Stockholm Environment Institute, Climate Analytics, E3G, International Institute for Sustainable Development and United Nations Environment Programme. https://doi.org/10.51414/sei2023.050

Additional references on existing fossil fuel infrastructure: 

• Tong, et al. (2019). Committed emissions from existing energy infrastructure jeopardize 1.5 °C climate target. Nature, 572, 373–377. https://doi.org/10.1038/s41586-019-1364-3
• Trout, et al. (2022). Existing fossil fuel extraction would phase out world beyond 1.5 °C. Environmental Research Letters, 17(6), 064010.https://doi.org/10.1088/1748-9326/ac6228

Additional references on proposed/potential new fossil fuel infrastructure:

• Kühne, et al. (2022). “Carbon Bombs”—Mapping key fossil fuel projects. Energy Policy, 166, 1–10. https://doi.org/10.1016/j.enpol.2022.112950  
• Byers, et al. (2022). AR6 Scenarios Database (1.0) [Data set]. Zenodo. https://doi.org/10.5281/zenodo.5886912 

4 Smith. et al. (2023). The State of Carbon Dioxide Removal – 1st Edition. https://www.stateofcdr.org