Emissions pathway to return global warming beneath 1 degree Celsius

Leading climate scientist Bill Hare has published the first emissions pathway to date that brings expected global warming beneath 1°C, albeit after peaking beneath 2°C and on the scale of centuries.

Date02 March 2009

Jan 22nd, 2009 By Chris McGrath

This is an immensely significant research topic for coral reefs as a rise in mean global temperature of 1°C appears to be the highest target that should be set if coral reefs are to be protected from serious degradation (see previous Climate Shifts post here).

Figure 2-1 depicts the global emissions pathway that Hare (2009: 25) suggests “is plausible technically” and “goes beyond the technically and economically feasible pathways published elsewhere”. It requires getting fossil CO2 emissions down to close to zero in 2050 and being carbon negative thereafter – a commitment to action that spans centuries.

Hare (2009: 27) suggests that under this emissions pathway “global temperatures should peak below 2 degrees Celsius around mid-century and begin a slow decline, dropping to present levels by the last half of the twenty-third century.”

The means of achieving such an emissions pathway, including being carbon negative after 2050, are discussed by Hare and other authors in subsequent chapters of the Worldwatch Institute publication, ‘State of the World 2009‘. This report is peer reviewed, but Hare will hopefully publish his new modelling in a peer reviewed climate journal shortly to improve its acceptance in the scientific community.

Hare (2009: 25) acknowledges that achieving negative CO2 emissions on a global scale will be extremely difficult and “evaluation of the implications of the technologies required to achieve this are only just beginning.”

Hare’s emissions pathway builds on the recent publication by Jim Hansen and his colleagues which argued “If humanity wishes to preserve a planet similar to that on which civilization developed and to which life on Earth is adapted, paleoclimate evidence and ongoing climate change suggest that CO2 will need to be reduced from its current 385 ppm to at most 350 ppm, but likely less than that.”

The ambition of the emissions pathway suggested by Hare (2009) is far beyond any contemplated in the mainstream policy debate at present but it is likely that such radical proposals will become much more prevalent in the future.


Hansen J, et al (2008), “Target Atmospheric CO2 – Where Should Humanity Aim? Open Atmospheric Sciences Journal
Hare WB (2009), “A safe landing for the climate”, Ch 2 in Starke L (ed), State of the World 2009: into a warming world (Worldwatch Institute)
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