Why do we so put much confidence in his conclusions?
Dr James Hansen is “one scientist.” True. But he is not alone. These new findings were published in “Target Atmospheric CO2: Where Should Humanity Aim?”The authors are:
James Hansen*,a,b, Makiko Satoa,b, Pushker Kharecha,a,b, David Beerling,c, Robert Bernerd,d
Valerie Masson-Delmottee,e, Mark Paganid,d, Maureen Raymof,f, Dana L. Royerg,g, and James C. Zachosh,h
aNASA/Goddard Institute for Space Studies, New York, NY 10025, USA
bColumbia University Earth Institute, New York, NY 10027, USA
cDept. Animal and Plant Sciences, University of Sheffield, Sheffield S10 2TN, UK
dDept. Geology and Geophysics, Yale University, New Haven, CT 06520-8109, USA
eLab. Des Sciences du Climat et l’Environnement/Institut Pierre Simon Laplace, CEA-CNRS-Universite de Versailles Saint-Quentin en Yvelines, CE Saclay, 91191, Gif-sur-Yvette, France
fDept. Earth Sciences, Boston University, Boston, MA 02215, USA
gDept. Earth and Environmental Sciences, Wesleyan University, Middletown, CT 06459-0139, USA
hEarth & Planetary Sciences Dept., University of California, Santa Cruz, Santa Cruz, CA 95064, USAThe 350 Abstract:
Paleoclimate data show that climate sensitivity is ~3°C for doubled CO2, including only fast feedback processes. Equilibrium sensitivity, including slower surface albedo feedbacks, is ~6°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.
As the Director of NASA’s Goddard Institute of Space Studies, Dr Hansen leads the largest group of climate scientists in the world. Finally, Dr Hansen first warned the US Congress in 1988. He was roundly ridiculed by both scientists and lay people. His conclusions then have been confirmed by observation and models.