Climate changed in steps in the past

September 10, 2020

An international study published in Science significantly improves the potential for understanding how the Earth's climate system evolved over the past 66 million years. The work reveals that the Earth system shifted abruptly between 4 distinct modes: hothouse, warmhouse, coolhouse, and icehouse during the period. The EU Horizon 2020 TiPES project contributed to the results.

The study, "An astronomically dated record of Earth's climate and its predictability over the last 66 Million Years", by Thomas Westerhold, MARUM, Bremen, Germany et. al presents a precisely dated paleoclimate record for the last 66 million years.

"The new dataset extends our knowledge on climate variability much further into the past and simultaneously has significantly improved temporal precision. It might, therefore, act as a new paleoclimate reference curve for researchers around the world," explains co-author Norbert Marwan of PIK-Potsdam, Germany.

Potsdam Institute for Climate Impact Research (PIK) is a principal investigator in the TiPES project, which is coordinated from the University of Copenhagen, Denmark.

The new dataset, CENOGRID has more detail and higher signal-to-noise ratio than any previous paleoclimate record covering the period. This means, climate science now has access to a longer series of precise paleoclimate data, which can be used to extract knowledge about the Earth system from the past.

"We now know more accurately when it was warmer or colder on the planet and we also have a better understanding of the underlying dynamics," explains first author Thomas Westerhold of MARUM.

Advanced statistical analysis of the new, accurately dated climate record confirmed 4 distinct climate modes which dominated the last 66 million years: Hothouse, warmhouse, coolhouse, and our current state: Ice-house.

"We were able to look more in details that were not visible at the first glance on the data," explains Dr. Norbert Marwan.

The shifts between states might have involved tipping points, which is the subject of further investigations.

The improved data resolution and dating of the evolution of past climate is an important contribution to climate science. Not least, because precise climate modeling, which is urgently needed today, relies on a good understanding of the Earth system.

Also, the quality of a climate model can be tested by having it simulate the climate of the past. Such a test is of course only possible if we know the evolution of the past climate in reasonable detail.

Thus, the work should lead to reduced uncertainty in predictions of future climate conditions.

In the study, sample material from the ocean floor, collected throughout the world for more than five decades through internationally coordinated expeditions of the International Ocean Discovery Program (IODP) and its predecessor programs was astronomically dated, using the so-called Milankovitch cycles.

The Milankovitch cycles are recurring variations in the Earth's orbit around the Sun. These variations influence the amount and distribution of solar energy reaching Earth. As it varies over time, regional climates fluctuate, leaving a climate signal in fossilized microscopic organisms.

The TiPES project is an EU Horizon 2020 interdisciplinary climate science project on tipping points in the Earth system, coordinated by The Niels Bohr Institute at the University of Copenhagen, Denmark.
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University of Copenhagen

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