Tectonic degassing drove global temperature trends since 20 Ma

Abstract

The Miocene Climatic Optimum (MCO) from ~17 to 14 million years ago (Ma) represents an enigmatic reversal in Cenozoic cooling. A synthesis of marine paleotemperature records shows that the MCO was a local maximum in global sea surface temperature superimposed on a period from at least 19 Ma to 10 Ma, during which global temperatures were on the order of 10°C warmer than at present. Our high-resolution global reconstruction of ocean crustal production, a proxy for tectonic degassing of carbon, suggests that crustal production rates were ~35% higher than modern rates until ~14 Ma, when production began to decline steeply along with global temperatures. The magnitude and timing of the inferred changes in tectonic degassing can account for the majority of long-term ice sheet and global temperature evolution since 20 Ma.

How temperature-dependent silicate weathering acts as Earth’s geological thermostat

“…Even though weathering of drylands could increase with increases in MAP from warming, their minimal weathering fluxes preclude large contributions to global weathering. Our estimate of 22 ± 3 kJ mol −1 is within the range of values inferred from inverse arguments based on recent global paleoclimate models (table S1C) [e.g., (12,63)]. Those low sensitivities were required within the paleoreconstruction models to reproduce reasonable atmospheric PCO 2 levels.…”

Deterministic icehouse and greenhouse climates throughout Earth history

“…Finally, a deterministic climate on million-year timescales requires a lack of non- There is mounting evidence from the geologic past that icehouse-greenhouse transitions spanning millions of years are driven by the balance of weathering and volcanism (Caves et al, 2016;Dalton et al, 2022;Herbert et al, 2022;McKenzie et al, 2016;McKenzie & Jiang, 2019), rather than irreversible nudges across a critical threshold (Pohl et al, 2014;Stap et al, 2017). Our analysis strengthens the theoretical foundation underlying this empirical evidence for a deterministic long-term climate.…”

“…6C). For reference, volcanic degassing may have varied over the course of the Cenozoic by greater than 4×10 12 moles/yr (Berner, 2006;Caves et al, 2016;Herbert et al, 2022;Van Der Meer et al, 2014). This bistability window further collapses when we assume a lower climate inertia by requiring long-term stable states to be stable for all orbital configurations (stable fraction of 1).…”

“…The mechanisms behind these long-term cycles remain a first-order question in the Earth sciences. One set of theories posits that these cycles are driven by external forcings to the Earth system that modify the long-term carbon cycle, such as changes in long-term solid Earth degassing of CO 2 (Berner, 1991(Berner, , 2004(Berner, , 2006Herbert et al, 2022;Lee et al, 2013;McKenzie et al, 2016;McKenzie & Jiang, 2019;Van Der Meer et al, 2014) or internal processes such as changes in the efficiency of weathering reactions that sequester CO 2 (Caves et al, 2016;Caves Rugenstein et al, 2019;Krissansen-Totton & Catling, 2017;Kump & Arthur, 1997;Macdonald et al, 2019;Swanson-Hysell & Macdonald, 2017). Under these theories, the state of global climate is deterministic-it can be unambiguously determined if the external forcings and internal processes are known.…”

The Impact of Different Atmospheric CO2 Concentrations on Large Scale Miocene Temperature Signatures

“…However, implementation of enhanced ocean mixing (Lohmann et al, 2022), state-of-the-art parameterizations of cloud-aerosol interactions (Feng et al, 2019;Kiehl & Shields, 2013;Lunt et al, 2021; and improved representation of tidal mixing (Green & Huber, 2013;Lohmann, 2020) might improve the ability of models to simulate Miocene warmth and to reduce disagreement between modeled and reconstructed meridional temperature gradients. Model simulations with elevated CO 2 concentration, up to 1,100 ppm as recently reconstructed for the Early-Middle Miocene including the MCO by Herbert et al (2022), might also provide a better fit between climate simulations and reconstructed temperatures.…”