Anthropogenic ocean acidification rate unprecedented during past 66 million years

Chair: Joellen Russell

Zeebe, Richard E. (1)*

1 School of Ocean and Earth Science and Technology, Department of Oceanography, University of Hawaii at Manoa, 1000 Pope Road, MSB 629, Honolulu, HI 96822. USA

Carbon release rates from anthropogenic sources have reached a record high of about 10 Pg C/y in 2015. However, due to uncertainties in the strength of climate system feedbacks, the full impact of the rapid carbon release on the Earth system is difficult to predict with confidence. Geologic analogues from past transient climate changes could provide invaluable constraints but only if the associated carbon release- and ocean acidification rates can be reliably reconstructed. We present a new technique – based on combined data-model analysis – to extract rates of change from the geological record, without the need for a stratigraphic age model. Given currently available records, we then show that the present anthropogenic carbon release- and acidification rate is unprecedented during the Cenozoic (past 66 million years) by at least an order of magnitude. Our results have important implications for our ability to use past analogues to predict future changes, including constraints on climate sensitivity, ocean acidification, and impacts on marine ecosystems. For example, the fact that we have effectively entered an era of ‘no analogue’ state presents fundamental challenges to constraining forward modeling. Furthermore, future ecosystem disruptions will likely exceed the relatively limited extinctions observed during climate aberrations throughout the Cenozoic.