In an article on the Eocene, a period in the Earth’s history relatively free of political controversy due to its having ended about 33.9 mya, Wikipedia blurts out something hidden in plain sight: “An issue arises, however, when trying to model the Eocene and reproduce the results that are found with the proxy data.” That “issue” being that, as usual, models meant to predict the future cannot even reproduce the past. “The models, while accurately predicting the tropics, tend to produce significantly cooler temperatures of up to 20 °C (36 °F) colder than the actual determined temperature at the poles. This error has been classified as the ‘equable climate problem’.” Or the “Whoa Nelly our models are busted” problem.
The Eocene, by the way, is not totally free of controversy because nothing climate-related is. (Or much of anything involving human beings including what you’d think are fairly innocuous hobbies.) But the issue with the Eocene is that late in that epoch the planet started cooling. Despite high levels of CO2.
Wikipedia of course ties the cooling neatly to CO2 dropping. “At the end of the Eocene Optimum, carbon dioxide began decreasing due to increased siliceous plankton productivity and marine carbon burial. At the beginning of the middle Eocene an event that may have triggered or helped with the draw down of carbon dioxide was the Azolla event at around 49 million years ago. With the equable climate during the early Eocene, warm temperatures in the arctic allowed for the growth of azolla, which is a floating aquatic fern, on the Arctic Ocean. Compared to current carbon dioxide levels, these azolla grew rapidly in the enhanced carbon dioxide levels found in the early Eocene. As these azolla sank into the Arctic Ocean, they became buried and sequestered their carbon into the seabed. This event could have led to a draw down of atmospheric carbon dioxide of up to 470 ppm.”
Could have. But even if it did it sounds like a good example not of runaway climate change but of a build-in negative feedback stabilizing mechanism involving the carbon cycle, if those hadn’t been cancelled. But as the article also says, when the Eocene yielded to the Oligocene “around 34 million years ago” it seems fairly clear that atmospheric CO2 was “around 750-800 ppm”. Uh, isn’t that level catastrophic warming territory?
The science being settled, more research is clearly needed. Including into the “Whoa Nelly problem” that climate models are created to say CO2 causes warming so they say it no matter what really happens.