forcefully laid out how stabilization at some theoretical 450 ppm or 550 ppm is not a viable strategy for having a climate condusive to human civilization
Where did the 450ppm figure come from? Has that been revised? When the capital development of a country becomes a by-product of the activities of a casino, the job is likely to be ill-done. — John M. Keynes
arXiv.org: [0804.1126] Target atmospheric CO2: Where should humanity aim? J. Hansen (1 and 2), M. Sato (1 and 2), P. Kharecha (1 and 2), D. Beerling (3), R. Berner (4), V. Masson-Delmotte (5), M. Pagani (4), M. Raymo (6), D. L. Royer (7), J. C. Zachos (8) ((1) NASA GISS, (2) Columbia Univ. Earth Institute, (3) Univ. Sheffield, (4) Yale Univ., (5) LSCE/IPSL, (6) Boston Univ., (7) Wesleyan Univ., (8) Univ. California Santa Cruz)
Paleoclimate data show that climate sensitivity is ~3 deg-C for doubled CO2, including only fast feedback processes. Equilibrium sensitivity, including slower surface albedo feedbacks, is ~6 deg-C for doubled CO2 for the range of climate states between glacial conditions and ice-free Antarctica. Decreasing CO2 was the main cause of a cooling trend that began 50 million years ago, large scale glaciation occurring when CO2 fell to 450 +/- 100 ppm, a level that will be exceeded within decades, barring prompt policy changes. 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. The largest uncertainty in the target arises from possible changes of non-CO2 forcings. An initial 350 ppm CO2 target may be achievable by phasing out coal use except where CO2 is captured and adopting agricultural and forestry practices that sequester carbon. If the present overshoot of this target CO2 is not brief, there is a possibility of seeding irreversible catastrophic effects.
Additional material supporting the article "Target atmospheric CO2: Where should humanity aim?"
Appreciate that you chose to pull the thread and look at Hansen's work yourself to gain your own understanding of / perspective on it. Blogging regularly at Get Energy Smart. NOW!!!
Hansen's point is that the science / analysis leading to 450 ppm (550 ppm, etc) seems to have been overly optimistic and that we can't afford (as civilization and, perhaps, species) to allow significantly higher levels, for significant time periods. Thus, we must not just slow Co2 growth and stabilize, but need to figure out how to move the clock (back) to a level that would enable climate stabilization in a range conducive to human civilization. Blogging regularly at Get Energy Smart. NOW!!!
Personally, I think that humanity will need to strive for using 'sequestration' (beneficial sequestration like biochar) to help drive down human contributions, as 'remediation' as we decarbonize the global economy. As we reduce direct emissions and expand processes like terra preta and biochar, perhaps we will cross a point where human action is actually contributing to reduction of CO2 / other GHG levels in the atmosphere. Blogging regularly at Get Energy Smart. NOW!!!
An initial 350 ppm CO2 target may be achievable by phasing out coal use except where CO2 is captured and adopting agricultural and forestry practices that sequester carbon. If the present overshoot of this target CO2 is not brief, there is a possibility of seeding irreversible catastrophic effects.
Yes, path is to eliminate coal (or go to near zero emission coal) while doing other practices that reduce emissions and foster greater absorption of CO2 ('sequestration' with benefits). Blogging regularly at Get Energy Smart. NOW!!!
Where did the 450ppm figure come from? Has that been revised?
I believe 450 ppm is the target figure for the Kyoto protocoll. Digging there might produce an answer as to where it comes from.
U.S. Stabilization Wedges: Scientific American
The United Nations Framework Convention on Climate Change (UNFCCC) establishes the objective of preventing "dangerous anthropogenic interference with the climate system." While a "non-dangerous" concentration level has not been defined under the UNFCCC and is not a purely scientific concept, the European Union has set a goal of avoiding an increase of more than 2 degrees Celsius from pre-industrial levels in order to avoid the most dangerous changes to climate. This target finds strong support in papers presented at a conference hosted by Prime Minister Tony Blair at the Hadley Center, Exeter, in February 2005.1 Meinshausen shows that greenhouse gas concentrations need to be stabilized below 450 ppm CO2-equivalent in order to provide a high level of confidence that the 2 degree target will not be exceeded in this century.2
The United Nations Framework Convention on Climate Change (UNFCCC) establishes the objective of preventing "dangerous anthropogenic interference with the climate system." While a "non-dangerous" concentration level has not been defined under the UNFCCC and is not a purely scientific concept, the European Union has set a goal of avoiding an increase of more than 2 degrees Celsius from pre-industrial levels in order to avoid the most dangerous changes to climate. This target finds strong support in papers presented at a conference hosted by Prime Minister Tony Blair at the Hadley Center, Exeter, in February 2005.1
Meinshausen shows that greenhouse gas concentrations need to be stabilized below 450 ppm CO2-equivalent in order to provide a high level of confidence that the 2 degree target will not be exceeded in this century.2
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