Earth System Sensitivity

Problem statement

We will conduct a systematic analysis of “Earth-system sensitivity as a function of time and climatic state” and address the question: “How do long-term feedbacks (primarily silicate and carbonate weathering), the carbon cycle and ecosystem changes affect the total interplay between greenhouse-gas release and removal and global temperatures?” This sensi- tivity acts beyond the traditionally studied equilibrium and steady-state but shorter-term Charney climate sensitivity. By using proxy-based reconstructions of the key parameters of the global carbon cycle (ocean alkalinity, ocean and atmospheric CO2 and other greenhouse gases, global carbonate burial and diagenesis, temperature) we will gain a unique view of the transient nature of Earth-system sensitivity characterizing Cenozoic background states and boundary conditions.

All of these efforts will involve biogeochemical cycles and the endogenic carbon exchange, as well as new developments for including biological mediation of these cycles. This work will incorporate and combine new proxy developments, such as linked temperature reconstructions with existing temperature proxies (e.g., Mg/Ca and clumped isotopes), thereby reducing uncertainty.

Hypothesis

Initially, we will test the hypothesis that Earth-system sensitivity varied during the Cenozoic and is greater during warmer climatic states. Factors controlling Earth-system sensitivity may include atmospher- ic pCO2, ice cover, sea level, and global mean temperature.

Linkages

This work will closely interact with the Recorder Theme 1, and will benefit from novel Earth-system modeling capabilities to be applied in the Enabler modeling, and will provide context for the research topic ice-ocean interactions.

Figure from Cluster Proposal: Earth-system sensitivity describes the sensitivity of temperature response to changes in radiative forcing, amplified by long-term feedbacks depending on the timescale considered, and dependent on the initial climatic state (Hansen et al., 2013). Top panel shows example parameters involved in determination of Earth-system sensitivity (at- mospheric CO2 and stable oxygen isotope values representing deep-water temperature and ice volume. The slope of ΔT vs. ΔpCO2 (lower panel) is an approximation of climate sensitivity, and a function of various forcings, biogeochem- ical processes and feedbacks (illustrated on right). The functional nature of the slope is currently poorly constrained. It could be constant (blue thick line labelled “constant sensitivity”) or progressively increasing with higher CO2 levels (thick orange line “increasing sensitivity”). Paleoproxies can be used to reconstruct past climate variables, and then allow a determination of time-dependent Earth-system sensitivity. Oxygen isotope data from De Vleeschouwer et al., 2017; Zachos et al., 2008. CO2 compilation modified from Beerling and Royer (2011).