Keywords: Paleo-CO2, global carbon cycle, paleoclimates

Abstract: Paleo-CO2 reconstructions are integral to understanding the evolution of Earth system processes and their interactions given that atmospheric CO2 concentrations are intrinsically linked to planetary function. Furthermore, past periods of major climate change, within both greenhouse and icehouse states, provide unique insights into the response of land-atmosphere-ocean interactions to warming induced climate change, in particular for times of pCO2 comparable to those projected for our future. How well the past can inform the future, however, depends on how well paleo-CO2 estimates can be constrained. Although CO2 estimates exist for much of the past half-billion years (the Phanerozoic), proxies used to reconstruct paleo-CO2, differ in their assumptions and degree of understanding, and many existing paleo-CO2 estimates do not meet modern proxy theory.

In this talk, I will first address present-day CO2 in the context of the geologic past and what it suggests about our future, and then discuss approaches to and challenges of reconstructing paleo-CO2 concentrations. I will then introduce the CO2 Proxy Integration Project (CO2PIP) as a path forward to advance the science of paleo-CO2 reconstruction and to build next-generation CO2 record for the Phanerozoic. This will include approaches that the CO2PIP Consortium is taking to modernize published paleo-CO2 records so that they meet modern proxy theory criteria and the modeling tools that are being developed to provide quantitative, data-driven CO2 reconstructions. To illustrate the potential of high temporal-resolution and modernized paleo-CO2 records to advance our understanding of how Earth surface processes and ecosystems responded to changing atmospheric CO2 concentrations, I will share a couple of examples of our work reconstructing CO2-climate-ecosystem interactions and feedbacks during a time (late Paleozoic Ice Age) when CO2 fluctuated within the range of Quaternary levels to those projected by socio-economic emission scenarios of this century. This deep-time interval was defined by CO2-driven abrupt (hyperthermal-scale) warmings that led to major changes in environmental conditions in the oceans and on land. If time permits, I’ll wrap up by discussing how the typically long-term processes of carbon cycling studied to interpret paleo-CO2 changes can be accelerated in soils of natural and working lands as a promising new CO2 removal technology capable of sequestering CO2 from the atmosphere in volumes and at rates relevant to climate change.