A tighter constraint on Earth-system sensitivity from long-term temperature and carbon-cycle observations

Abstract

The long-term temperature response to a given change in CO2 forcing, or Earth-system sensitivity (ESS), is a key parameter quantifying our understanding about the relationship between changes in Earth’s radiative forcing and the resulting long-term Earth-system response. Current ESS estimates are subject to sizable uncertainties. Long-term carbon cycle models can provide a useful avenue to constrain ESS, but previous efforts either use rather informal statistical approaches or focus on discrete paleoevents. Here, we improve on previous ESS estimates by using a Bayesian approach to fuse deep-time CO2 and temperature data over the last 420 Myrs with a long-term carbon cycle model. Our median ESS estimate of 3.4 °C (2.6-4.7 °C; 5-95% range) shows a narrower range than previous assessments. We show that weaker chemical weathering relative to the a priori model configuration via reduced weatherable land area yields better agreement with temperature records during the Cretaceous. Research into improving the understanding about these weathering mechanisms hence provides potentially powerful avenues to further constrain this fundamental Earth-system property.

Cenozoic Proxy Constraints on Earth System Sensitivity to Greenhouse Gases

“…An amplification of ESS in the late Cenozoic has long been suspected (Hansen et al, 2008) but our results are interesting in two respects. First, the glacial amplification factor inferred here (2.2, 1.5-3.4, 95% interval) is on the high end of previous studies which draw on the output of the geological GEOCARB carbon cycle model and favor an amplification factor of about 2 (Park & Royer, 2011;Wong et al, 2021). Second, the transition to higher ESS in GEOCARB is prescribed to occur in the late Eocene (Park & Royer, 2011) due to the rapid emplacement of the Antarctic ice sheet.…”

Compression complexity with ordinal patterns for robust causal inference in irregularly sampled time series

“…Mills et al have compiled independent estimates of global average surface temperature and atmospheric CO concentration for the Phanerozoic eon. These paleoclimate proxy records span the last 424 million years 62 and have been used and made available in the study by Wong et al 63 . One data point for both CO and temperature recordings were available for each million year period and was used in our analysis to check for causal interaction between between the two.…”

Compression-Complexity with Ordinal Patterns for Robust Causal Inference in Irregularly-Sampled Time Series

“…Millenial scale CO 2 -temperature recordings: Mills et al have compiled independent estimates of global average surface temperature and atmospheric CO 2 concentration for the Phanerozoic eon. These paleoclimate proxy records span the last 424 million years [62] and have been used and made available in the study by Wong et al [63]. One data point for both CO 2 and temperature recordings were available for each million year period and was used in our analysis to check for causal interaction between between the two.…”