Ancient ocean temperatures outline a puzzling period in Earth’s climate history

Paper: The enigma of Oligocene climate and global surface temperature evolution

Featured image: Figure 1 from O’Brien et al. (2020). Paleogeographic reconstruction of the late Oligocene world, with continents and oceans in slightly different positions than today. Symbols indicate paleo-locations of ocean sediments that these scientists discuss in their paper, with stars indicating sites where they estimated Oligocene temperatures.

Authors: Charlotte L. O’Brien, Matthew Huber, Ellen Thomas, Mark Pagani, James R. Super, Leanne E. Elder, Pincelli M. Hull

We know that the amount of carbon dioxide in the atmosphere strongly affects climate –and temperature – on Earth. As carbon dioxide concentrations increase, so does average global temperature; this pattern is clear from direct historical measurements and ice core records going back hundreds of thousands of years. Nevertheless, it’s important to understand how this relationship operated in the past (for example, during times when there was less ice in the cold polar regions of the globe). A new study suggests that, millions of years in the past, the simple relationship between carbon dioxide and temperatures may not have been so clearcut.

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New 23 million year record of atmospheric carbon dioxide highlights current human influence on the atmosphere

Paper: A 23 m.y. record of low atmospheric CO2

Featured image: Modern vascular land plants (Raphanus sativus), growing in a carbon dioxide experiment (Figure 1A from Jahren et al., 2008)

Authors: Ying Cui, Brian A. Schubert, A. Hope Jahren

Carbon dioxide is a greenhouse gas, trapping warmth within the Earth’s atmosphere. Sixty years of measurements on Hawaii’s Mauna Loa summit have shown rising amounts of carbon dioxide in our atmosphere. In addition, the carbon dioxide levels in our modern atmosphere are  significantly higher than  those we have seen on Earth over the last 800,000 years, according to measurements on bubbles of ancient air trapped in  Antarctic ice. When combined with measurements of global temperatures, these direct measurements are irrefutable evidence for rapid modern climate change. However, understanding our current position relative to Earth’s climate farther back in time is trickier, since scientists have to estimate atmospheric composition indirectly (through a “proxy”). A new study tackles this problem with a new method of estimating past carbon dioxide, showing  that modern carbon dioxide levels have been unprecedented since at least 7 million years ago.

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Cave formations show link between ice ages and the tilt of Earth’s axis

Paper: Persistent influence of obliquity on ice age terminations since the Middle Pleistocene transition

Featured image: Stalagmites captured by mareke on Pixabay

Authors: Petra Bajo, Russell N. Drysdale, Jon D. Woodhead, John C. Hellstrom, David Hodell, Patrizia Ferretti, Antje H.L. Voelker, Giovanni Zanchetta, Teresa Rodrigues, Eric Wolff, Jonathan Tyler, Silvia Frisia, Christoph Spötl, Anthony E. Fallick

Our planet has been circling and spinning in a wobbly dance around the Sun for billions of years. The exact motions of this dance- governed by Earth’s near-circular orbit (eccentricity), the tilt of its axis, and the orientation of the tilted axis in space (precession) fluctuate predictably. Variations in this planetary dance have changed the amount and distribution of sunlight reaching Earth’s surface through time, and have determined when the planet experienced long periods of cold temperatures and growth of massive ice caps on the continents (ice ages). However, scientists have not been so sure about which planetary motion is the most important for the timing of ice ages. New research uses climate information stored in caves to precisely link these motions to ice ages, showing that axis tilt may be the most important position in the dance when it comes to pulling Earth’s climate out of those frigid times.  

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