I Was Born Under a Wandering Star

Dave Middleton at WUWT sees a report that PETM Caused by Passing Star?

The Paleocene Eocene Thermal Maximum (PETM) was a geologically brief spike in temperatures, during the warmest climatic episode of the Cenozoic Era.

We are often told that the warmth of the Early Paleogene was driven by CO2; and that the cool-down from the Late Paleogene, into the Neogene and Quaternary Periods was driven by a draw-down of atmospheric CO2; however there is scant evidence for this hypothesis . Despite the paucity of geological evidence, the notion of a CO2-driven climate has apparently become a paradigm. This paradigm didn’t exist in the 1970’s.

Suggestion that changing carbon dioxide content of the atmosphere could be a major factor in climate change dates from 1861, when it was proposed by British physicist John Tyndall.
[…]
Unfortunately we cannot estimate accurately changes of past CO2 content of either atmosphere or oceans, nor is there any firm quantitative basis for estimating the the magnitude of drop in carbon dioxide content necessary to trigger glaciation. Moreover the entire concept of an atmospheric greenhouse effect is controversial, for the rate of ocean-atmosphere equalization is uncertain.Dott, Robert H. & Roger L. Batten. Evolution of the Earth. McGraw-Hill, Inc. Second Edition 1976. p. 441.

While methods of estimating past CO2 levels have improved, the Early Paleogene is still poorly understood, with estimates ranging from 300 to 3,500 ppm.

And what has that got to do with wandering stars?

“And now for something completely different…” Earth’s Orbit Mysteriously Altered by Chance Encounter Million of Years Ago  

By MICHELLE STARR

A grazing encounter between the Solar System and a passing star could once have changed Earth’s orbit enough to wreak havoc on the climate, new research has found.

Around 56 million years ago, at the boundary between the Paleocene and Eocene, Earth’s temperature warmed by up to 8 °C (14.4 °F). This has always been a bit of a puzzle – but planetary scientist Nathan Kaib of the Planetary Science Institute and astrophysicist Sean Raymond of the Laboratory of Astrophysics of Bordeaux suggest a chance encounter may have been the culprit. Their simulations show that a star passing by the Solar System could have introduced enough disruption to planetary orbits to nudge Earth slightly off course.

“One reason this is important is because the geologic record shows that changes in the Earth’s orbital eccentricity accompany fluctuations in the Earth’s climate,” Kaib says. “If we want to best search for the causes of ancient climate anomalies, it is important to have an idea of what Earth’s orbit looked like during those episodes.”
[…]
Kaib and Raymond wanted to know if a passing star could have a similar effect, even from a significant distance. Their work focused on a single known event. Some 2.8 million years ago, a Sun-like star called HD 7977 passed the Solar System, potentially so closely that it flew inside the Oort Cloud.
[…]
HD 7977 is one star, and the only flyby we can confidently identify. But scientists have estimated that a star passes by within 50,000 astronomical units every million years or so, and within 10,000 astronomical units every 20 million years or so. This means that it’s entirely possible that a passing star has affected Earth’s climate in the past – and may even have played a role in the thermal maximum.