Orbital Changes Triggered Ancient Global Warming

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Orbital Changes Triggered Ancient Global Warming

A group of scientists from various countries have proposed that a change in Earth’s orbit leading to higher temperatures may have contributed to the sudden global warming event that occurred 56 million years ago. This event, called the Paleocene-Eocene Thermal Maximum (PETM), is similar to the current climate change happening today.

According to Lee Kump, a professor of geosciences at Penn State University, the PETM is the closest example in the geological record to the current and future effects of climate change. The researchers are interested in understanding what caused the event and the rate of carbon emissions during it.

The scientists used a method called astrochronology to analyze core samples from a well-preserved record of the PETM found near the coast of Maryland. Astrochronology is a method of dating sedimentary layers based on the orbital patterns, known as Milankovitch cycles, that occur over long periods of time.

The researchers found that the shape of Earth’s orbit, specifically its eccentricity, and the wobble in its rotation, or precession, were conducive to higher temperatures at the start of the Paleocene-Eocene Thermal Maximum (PETM) event. These orbital configurations may have played a role in initiating the event.

The study’s lead author, Lee Kump, suggests that an orbital trigger may have led to the carbon release that caused several degrees of global warming during the PETM, which is different from the more popular interpretation that massive volcanism released the carbon and triggered the event.

The study, published in the journal Nature Communications, found that the onset of the PETM lasted about 6,000 years. This is a shorter duration than previous estimates, which ranged from several years to tens of thousands of years. This information is important to understand the rate at which carbon was released into the atmosphere.

The lead author, Mingsong Li, states that the study allows for refinement of carbon cycle models to better understand how the planet reacts to an injection of carbon over these timescales and to narrow down the possibilities for the source of the carbon that drove the PETM.

The study found that about 1.5 gigatons of carbon were released per year during the 6,000-year onset of the PETM, which is close to an order of magnitude slower than the current rate of carbon emissions. This highlights the concern that today’s rate of carbon emissions is 5 to 10 times higher than the rate of emissions during the PETM.

The scientists used time series analysis of calcium content and magnetic susceptibility found in the cores, which are proxies for changes in orbital cycles, to estimate the pacing of the PETM.

Earth’s orbit varies in predictable, calculable ways due to gravitational interactions with the sun and other planets in the solar system. These changes impact how much sunlight reaches Earth and its geographic distribution, which in turn influence the climate.

These orbital changes are recorded in the geologic record because they affect the climate, influencing the productivity of marine and terrestrial organisms, the amount of rainfall, erosion on continents, and the amount of sediment carried into the ocean environment, according to Kump.

Reference: “Astrochronology of the Paleocene-Eocene Thermal Maximum on the Atlantic Coastal Plain” by Mingsong Li, Timothy J. Bralower, Lee R. Kump, Jean M. Self-Trail, James C. Zachos, William D. Rush and Marci M. Robinson, 24 September 2022, Nature Communications.
DOI: 10.1038/s41467-022-33390-x

The study was funded by the National Key R&D Program of China and the Heising-Simons Foundation.

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