Read this new paper at: http://www.earth-syst-dynam.net/8/577/2017/esd-8-577-2017-discussion.html
1. Global warming in the past 50 years has raised global temperature (Fig. 1) well above the prior range of the Holocene (the current interglacial period approximatly the 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 1.5C (the aspirational goal of the Paris Agreement) if rapid reductions of global CO2 (at least 3%/year) begin by 2021 and if there is no net growth of other climate forcings (Fig. 2). However, 1.5C global warming exceeds estimated Eemian termperature 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 emissions reductions had begun at that time and if there were a global program for reforestation and improved agricultural and foresty 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.