Something Else ‘Used to’ Drive Climate Changes, Ancient Ice Cores Reveal

The researchers conclude: ‘It wasn’t always greenhouse gases’, because for very long periods temperatures were found to be ‘relatively stable’. But the article here still pushes greenhouse gas theory as being applicable to the current era. Jo Nova covers it in more detail here.
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According to the findings of two new papers published in Nature, at certain transition points ocean temperatures could have had a greater influence over Earth’s climate than greenhouse gases, says Science Alert.

Two research teams analyzed ice cores extracted from the Allan Hills, a blue ice region of Antarctica. The Allan Hills cores are samples of some of the world’s oldest ice, with some dating as far back as 6 million years ago.
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Woods Hole Oceanographic Institute paleoclimatologist Sarah Shackleton led an international team of researchers in the study focused on global ocean temperatures across the past 3 million years.

Dissolved xenon and krypton, two noble gases that dissolve in seawater at different temperatures, provided them with a way of estimating the ocean’s heat.

These proxy measurements suggest the ocean cooled drastically around 2.7 million years ago, roughly matching up with the Plio-Pleistocene Transition, when the Earth gradually shifted from a warmer to cooler climate that led to glacier formation across large parts of the Northern Hemisphere.

The ice core data also suggests that average ocean temperatures stayed relatively stable across the Mid-Pleistocene Transition, another shift in glacial cycles that occurred between 1.2 and 0.8 million years ago.

Meanwhile, from the same ice cores, a team led by Oregon State University geochemist Julia Marks-Peterson found atmospheric levels of carbon dioxide and methane were “broadly stable” across the past 3 million years.
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As Cambridge climatologist Eric Wolff writes in an accompanying commentary article, this suggests that either ice-sheet growth and survival was “exquisitely sensitive” to minuscule changes in carbon dioxide – or past changes in Earth’s climate may have been driven by something else.
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Lead researcher: “Exactly what these records capture in terms of exactly how smooth or exactly how much we’re averaging over a glacial versus interglacial conditions is still an outstanding question.”
[Talkshop comment – so is the ‘something else’].

Full article here.