How Equilibrium Climate Sensitivity is WORSE than Expected; Dependent on Initial Temperature: 1 of 3 // Oct 4, 2020

Part 1: I chat in detail in a three video series on how today’s climate and rate of change of climate related to the Eocene and PETM (Paleocene-Eocene Thermal Maximum). Despite recent advances, the link between evolution of atmospheric CO2 and climate during the Eocene greenhouse period remains unclear. Modelling studies suggest that to achieve the global warmth that characterized the early Eocene, warmer climates must be more sensitive to CO2 forcing than colder climates.

In other words, climate sensitivity (temperature vs CO2 level) depends on the starting conditions. In the new peer-reviewed paper that I discuss, they test this assertion in the geological record by combining a new high-resolution boron isotope-based CO2 record with novel estimates of Global Mean Temperature.

They find that Equilibrium Climate Sensitivity (ECS) was indeed higher during the warmest intervals of the Eocene, agreeing well with recent model simulations, and declined through the Eocene as global climate cooled. These observations indicate that the canonical IPCC range of ECS (1.5 to 4.5 °C per doubling) is unlikely to be appropriate for high-CO2 warm climates of the past, and the state dependency of ECS may play an increasingly important role in determining the state of future climate as the Earth continues to warm. In other words, we are fucked.
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New Peer-Reviewed Research: Equilibrium Climate Sensitivity is Worse that We Thought: Part 2 of 3 // Oct 4, 2020

Second video:

Ref 1:  Nature Communications volume 11, Article number: 4436 (2020), Published: 07 September 2020:  Proxy evidence for state-dependence of climate sensitivity in the Eocene greenhouse
Anagnostou, John,  Babila, Sexton, Ridgwell, Lunt, Pearson, Chalk, Pancost Foster:

‘The Eocene Epoch is the most recent greenhouse period in Earth’s history. Atmospheric carbon dioxide (CO2) and temperature peaked in the early Eocene, and both declined towards the late Eocene, ultimately leading to an icehouse state at the Eocene-Oligocene Transition.

However, to better constrain the potential mechanisms driving the early Eocene warmth and the subsequent cooling, high-resolution records of CO2 and temperature are required. While obtaining continuous marine records of temperature through this interval has been an ongoing effort, similar records for CO2, are fragmented and of low temporal resolution with large uncertainties, and thus remain insufficient to fully characterize the climate dynamics of the Eocene.’
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Paleocene-Eocene Thermal Maximum (56 million years ago) informs us on today’s Climate: Part 3 of 3 // Oct 5, 2020

Third video.

Ref 2:  ‘What Are “Proxy” Data?‘  ‘In paleoclimatology, or the study of past climates, scientists use what is known as proxy data to reconstruct past climate conditions. These proxy data are preserved physical characteristics of the environment that can stand in for direct measurements. Paleoclimatologists gather proxy data from natural recorders of climate variability such as tree rings, ice cores, fossil pollen, ocean sediments, corals and historical data. By analyzing records taken from these and other proxy sources, scientists can extend our understanding of climate far beyond the instrumental record‘.

Ref 3:  ‘The Perplexing PETM, Posted on 23 September 2014.

‘Rapid change and environmental turmoil
At the onset of the PETM, oceans acidified in less than 10,000 years (a geological blink) by around 0.3pH units as average surface ocean temperatures across the planet rose by 4° to 5°C (7-9°F), with the subsurface oceans warming by 5-6°C (9-11°F). Ecosystems across the world were plunged into turmoil, with poleward migrations, decline of reefs, extinctions of some sea-bottom-living creatures, and in some places 20% of land plants went extinct while plant diversity dropped by more than a third.

‘In mammals the effects included strong natural selection for small body size, and high species turnover, though there was no vertebrate mass extinction. Globally the resulting climate of the early Eocene was up to 15°C (27°F) warmer than today, supporting lush vegetation on Antarctica and the Arctic‘.
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