Toward a Cenozoic history of atmospheric CO 2

• Published in: Science
• Main Authors: Hönisch, Bärbel, Royer, Dana L, Breecker, Daniel O, Polissar, Pratigya J, Bowen, Gabriel J, Henehan, Michael J, Cui, Ying, Steinthorsdottir, Margret, McElwain, Jennifer C, Kohn, Matthew J, Pearson, Ann, Phelps, Samuel R, Uno, Kevin T, Ridgwell, Andy, Anagnostou, Eleni, Austermann, Jacqueline, Badger, Marcus P S, Barclay, Richard S, Bijl, Peter K, Chalk, Thomas B, Scotese, Christopher R, de la Vega, Elwyn, DeConto, Robert M, Dyez, Kelsey A, Ferrini, Vicki, Franks, Peter J, Giulivi, Claudia F, Gutjahr, Marcus, Harper, Dustin T, Haynes, Laura L, Huber, Matthew, Snell, Kathryn E, Keisling, Benjamin A, Konrad, Wilfried, Lowenstein, Tim K, Malinverno, Alberto, Guillermic, Maxence, Mejía, Luz María, Milligan, Joseph N, Morton, John J, Nordt, Lee, Whiteford, Ross, Roth-Nebelsick, Anita, Rugenstein, Jeremy K C, Schaller, Morgan F, Sheldon, Nathan D, Sosdian, Sindia, Wilkes, Elise B, Witkowski, Caitlyn R, Rae, James W B
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2023
• Subjects: Greenland; Antarc*; Antarctica
• Online Access: https://research-portal.st-andrews.ac.uk/en/publications/b99ca32f-7f0b-48d4-a8dd-fa3619522054; https://doi.org/10.1126/science.adi5177; https://research-repository.st-andrews.ac.uk/bitstream/10023/30475/1/CenCO2PIP_2023_Science_Cenzoic-history_CC.pdf

INTRODUCTION Anthropogenic carbon dioxide (CO 2 ) emissions have driven an increase in the global atmospheric CO 2 concentration from 280 parts per million (ppm) before industrialization to an annual average of 419 ppm in 2022, corresponding to an increase in global mean surface temperature (GMST) of 1.1°C over the same period. If global CO 2 emissions continue to rise, atmospheric CO 2 could exceed 800 ppm by the year 2100. This begs the question of where our climate is headed. The geologic record is replete with both brief and extended intervals of CO 2 concentration higher than today and thus provides opportunities to project the response of the future climate system to increasing CO 2 . For example, it has been estimated that global surface temperature 50 million years ago (Ma) was ~12°C higher than today, in tandem with atmospheric CO 2 concentrations some 500 ppm higher (i.e., more than doubled) than present-day values. Consistent with these estimates, Antarctica and Greenland were free of ice at that time. However, reconstructing these values prior to direct instrumental measurements requires the use of paleoproxies—measurable properties of geological archives that are closely, but only indirectly, related to the parameter in question (e.g., temperature, CO 2 ). To date, at least eight different proxies from both terrestrial and marine archives have been developed and applied to reconstruct paleo-CO 2 , but their underlying assumptions have been revised over time, and published reconstructions are not always consistent. This uncertainty complicates quantification of the climate responses to the ongoing rise of atmospheric CO 2 concentrations. RATIONALE Although earlier studies have compiled published paleo-CO 2 estimates, those studies typically applied only limited proxy vetting, included estimates that were made before the proxies were sufficiently validated, and/or focused on only a subset of available proxy data. The international consortium of the Cenozoic CO 2 Proxy Integration Project (CenCO 2 PIP) ...