Target Atmospheric CO: Where Should Humanity Aim?

• Published in: The Open Atmospheric Science Journal
• Main Authors: Hansen, James, Sato, Makiko, Kharecha, Pushker, Beerling, David, Berner, Robert, Masson-Delmotte, Valérie, Pagani, Mark, Raymo, Maureen, Royer, Dana, Zachos, James
• Other Authors: Laboratoire des Sciences du Climat et de l'Environnement Gif-sur-Yvette (LSCE), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Direction de Recherche Fondamentale (CEA) (DRF (CEA)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA), Glaces et Continents, Climats et Isotopes Stables (GLACCIOS), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Direction de Recherche Fondamentale (CEA) (DRF (CEA))
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2008
• Subjects: Climate change; climate sensitivity; global warming; [SDU.OCEAN]Sciences of the Universe [physics]/Ocean; Atmosphere; [SDU.ENVI]Sciences of the Universe [physics]/Continental interfaces; environment; Antarc*; Antarctica
• Online Access: https://hal.science/hal-03192851; https://hal.science/hal-03192851/document; https://hal.science/hal-03192851/file/TOASCJ-2-217.pdf; https://doi.org/10.2174/1874282300802010217

International audience Paleoclimate d ata show that climate sensitivity is ~3°C for doubled CO 2 , including only fast feedback processes. Equilibrium sensitivity, including slower surface albedo feedbacks, i s ~6°C for doubled CO 2 fo r th e ran ge o f cl imate states between glacial conditions and ice-free Antarctica. Decreasing CO 2 was the main cause of a cooling trend that began 50 m illion yea rs a go, the pl anet bei ng ne arly i ce-free unt il CO 2 f ell to 450 ± 100 ppm ba rring pr ompt pol icy changes, th at c ritical l evel w ill b e p assed, in th e opposite di rection, w ithin de cades. If hum anity w ishes t o pr eserve a planet similar to that on w hich civilization developed and to which life on Ea rth is adapted, p aleoclimate evidence and ongoing climate change suggest that CO 2 will need to be reduced from its current 385 ppm to at most 350 ppm, but likely less than that. The largest uncertainty in the target arises from possible changes of non-CO 2 forcings. An initial 350 ppm CO 2 target may be achievable by phasing out coal use except where CO 2 is captured and adopting agricultural and forestry practices that sequester carbon. If the present overshoot of this target CO 2 is not brief, there is a possibility of seeding irreversible catastrophic effects.