Conclusions include:
1. Global warming in the past 50 years has raised global temperature (Fig. 1) 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.
2. 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 (Fig. 2). However, 1.5°C global warming exceeds estimated Eemian
temperature and is not an appropriate goal.
3. The growth rate of greenhouse gas climate forcing has accelerated markedly in the past several
years (Fig. 3), 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.
4. An appropriate goal is to return global temperature to the Holocene range with 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.
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