By James Hansen

18 July 2017

(Earth Institute) – The paper is published today in Earth System Dynamics. There is also a video with Sophie and Jim.Conclusions include: Global warming in the past 50 years has raised global temperature well above the prior range in the Holocene (the current interglacial period, approximately the past 11,700 years) to the level of the Eemian period (130,000 to 115,000 years ago), when sea level was 6-9 meters (20-30 feet) higher than today. Global warming can be held below 1.5°C (the aspirational goal of the Paris Agreement) if rapid reductions of global CO2 emission (at least 3%/year) begin by 2021 and if there is no net growth of other climate forcings. However, 1.5°C global warming exceeds estimated Eemian temperature and is not an appropriate goal. The growth rate of greenhouse gas climate forcing has accelerated markedly in the past several years, a conclusion starkly at odds with the common narrative that the world has recently turned the corner toward a solution of the global warming problem [cf. NOAA’s greenhouse gas index up 40 percent since 1990 – Carbon dioxide increase is accelerating]. An appropriate goal is to return global temperature to the Holocene range within a century. Such a goal was still achievable in 2013 if rapid emission reductions had begun at that time and if there were a global program for reforestation and improved agricultural and forestry practices. Now climate restoration this century would also require substantial technological extraction of CO2 from the air. If rapid emission reductions do not begin soon, the burden placed on young people to extract CO2 emitted by prior generations may become implausibly difficult and costly. Author and Sophie Kivlehan quotes Michael Prather (re point #3 above): “What is particularly worrying about the recent uptick in greenhouse gas climate forcing, is that it is driven in part by the recent surge in methane abundance, while reduced methane is one of the requirements in most pathways to reduced greenhouse gas forcing.”Karina von Schuckmann: “The Earth is out of energy balance. Associated symptoms are contemporary sea level rise related to ice melt and warming oceans, as well as worldwide increased surface temperatures, extreme events, coastal flooding and drought. Unequivocal urgent international action is needed.”Sophie Kivlehan: “I’m excited for Young People’s Burden to provide support for Juliana v United States. This paper secures a strong and legitimate foundation for which young people can fight for our right to life, and a viable future. We need the adults to wake up and listen.”

Jim Hansen: (1) It is significant and gratifying that global leaders in relevant disciplines (e.g., Earth’s energy balance, paleoclimate including Holocene studies, sea level, atmospheric chemistry, carbon cycle) agreed to work together on this effort, not only assuring excellence in their specialties, but also helping with the overall structure of the paper and its conclusions.(2) The publication process, starting with a Discussion version of the paper available to the public and the research community, was very effective, and we thank the editor and reviewers for their substantial efforts. The anonymous formal reviews were very helpful. This final version of the paper improves the clarity of the science and conclusions. New conclusions we now stress, which were only implicit in the Discussion version, include: a) Even the aspirational goal of the Paris Agreement, to keep global warming below 1.5°C, is not adequate. b) A current narrative, that humanity has turned the corner and is moving toward solving the global warming problem, is wrong. Atmospheric greenhouse gases are not only continuing to increase rapidly, their growth rate has actually accelerated rapidly in the past several years.

Young People’s Burden: Requirement of Negative CO2 Emissions

ABSTRACT: Global temperature is a fundamental climate metric highly correlated with sea level, which implies that keeping shorelines near their present location requires keeping global temperature within or close to its preindustrial Holocene range. However, global temperature excluding short-term variability now exceeds +1 °C relative to the 1880–1920 mean and annual 2016 global temperature was almost +1.3 °C. We show that global temperature has risen well out of the Holocene range and Earth is now as warm as it was during the prior (Eemian) interglacial period, when sea level reached 6–9 m higher than today. Further, Earth is out of energy balance with present atmospheric composition, implying that more warming is in the pipeline, and we show that the growth rate of greenhouse gas climate forcing has accelerated markedly in the past decade. The rapidity of ice sheet and sea level response to global temperature is difficult to predict, but is dependent on the magnitude of warming. Targets for limiting global warming thus, at minimum, should aim to avoid leaving global temperature at Eemian or higher levels for centuries. Such targets now require negative emissions, i.e., extraction of CO2 from the air. If phasedown of fossil fuel emissions begins soon, improved agricultural and forestry practices, including reforestation and steps to improve soil fertility and increase its carbon content, may provide much of the necessary CO2 extraction. In that case, the magnitude and duration of global temperature excursion above the natural range of the current interglacial (Holocene) could be limited and irreversible climate impacts could be minimized. In contrast, continued high fossil fuel emissions today place a burden on young people to undertake massive technological CO2 extraction if they are to limit climate change and its consequences. Proposed methods of extraction such as bioenergy with carbon capture and storage (BECCS) or air capture of CO2 have minimal estimated costs of USD 89–535 trillion this century and also have large risks and uncertain feasibility. Continued high fossil fuel emissions unarguably sentences young people to either a massive, implausible cleanup or growing deleterious climate impacts or both.

Young people’s burden: requirement of negative CO2 emissions