Study: Temperatures Not Experienced In Last 420 Million Years Could Arrive By 23rd Century With Continuing Fossil Fuel Use

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Over the next couple of hundred years, temperatures could rise to levels not experienced at any point in the last 420 million years, if fossil fuel reserves continue to be extracted and burnt, according to new research from the University of Southampton.

The research notes that over the next 100–200 years, if there are no major changes to fossil fuel use patterns, and all economically recoverable fossil fuels get burnt, atmospheric carbon dioxide levels will rise to those not seen since the Triassic, some 200 million years ago (~2000 ppm). (Note: The Sun was much dimmer back then, so even if atmospheric CO2 levels are equal, temperatures now would be higher.)

The new research was based on the compilation of more than “1200 estimates of ancient atmospheric carbon dioxide (CO2) concentrations … dating back nearly half a billion years.” In other words, it was a deep dive.

“It concludes that if humanity burns all available fossil fuels in the future, the levels of CO2 contained in the atmosphere may have no geologically-preserved equivalent during this 420 million year period.”

These estimates included a variety of very different data points — including those based on fossilized plants, those based on the boron isotopic composition of fossil shells, those based on the isotopic composition of carbon in soils and the oceans, and others.

Living Ginkgo leaf (left) and fossil (right). Density of stomata in such leaves is proxy of atmospheric CO2 in past. Image by Dana Royer

The lead author of the new work, Gavin Foster, the Professor of Isotope Geochemistry at the University of Southampton, commented: “We cannot directly measure CO2 concentrations from millions of years ago. Instead we rely on indirect ‘proxies’ in the rock record. In this study, we compiled all the available published data from several different types of proxy to produce a continuous record of ancient CO2 levels.”

The press release continued: “This wealth of data shows that CO2 concentrations have naturally fluctuated on multi-million year timescales over this period, from around 200–400 parts per million (ppm) during cold ‘icehouse’ periods to up to 3000 ppm during intervening warm ‘greenhouse’ periods. Although evidence tells us our climate has fluctuated greatly in the past (with the Earth currently in a colder period), it also shows the current speed of climate change is highly unusual.”

With regard to current atmospheric carbon dioxide levels, they are now around ~408 ppm or so — up from around 280 ppm prior to the beginning of widescale industrial activity a few hundred years ago. So, levels are already quite high for an interglacial period, much higher than in any recent times.

With regard to the fact that the Sun is brighter now than it was the last time that atmospheric carbon dioxide levels were as high as where we are possibly headed, the Professor of Climate Science at the University of Bristol, Dan Lunt, commented: “Due to nuclear reactions in stars, like our sun, over time they become brighter. This means that, although carbon dioxide concentrations were high hundreds of millions of years ago, the net warming effect of CO2 and sunlight was less. Our new CO2 compilation appears on average to have gradually declined over time by about 3–4 ppm per million years. This may not sound like much, but it is actually just about enough to cancel out the warming effect caused by the sun brightening through time, so in the long-term it appears the net effect of both was pretty much constant on average.”

A co-author of the new work, Professor Dana Royer from Wesleyan University, noted: “Up until now it’s been a bit of a puzzle as to why, despite the sun’s output having increased slowly over time, scant evidence exists for any similar long-term warming of the climate. Our finding of little change in the net climate forcing offers an explanation for why Earth’s climate has remained relatively stable, and within the bounds suitable for life for all this time.”

Professor Foster concluded his commentary with this statement: “However, because the Sun was dimmer back then, the net climate forcing 200 million years ago was lower than we would experience in such a high CO2 future. So not only will the resultant climate change be faster than anything the Earth has seen for millions of years, the climate that will exist is likely to have no natural counterpart, as far as we can tell, in at least the last 420 million years.”

While this work is of course very relevant, it doesn’t take into account the human side of things — which is likely to crap out in many ways before all recoverable fossil fuel reserves are exploited.

To be clear, the rising problems of water scarcity in some regions, overpopulation, resource and synthetic fertilizer scarcity, growing microbial resistance to non-systemic antibiotics, rising seas, extreme levels of soil erosion (and decreasing crop yields), water and air pollution, mass migration, cultural conflict, etc., are likely to put a damper on things somewhat over the coming centuries.

Someone will probably comment below that renewables and electric cars will allow extreme anthropogenic climate change to be avoided, but as carbon dioxide levels are still increasing at an ever-increasing rate, and there have yet to be any serious efforts made to back away from fossil fuels, I’ll say that I’m skeptical, and will believe it when it happens. (If Norway is an example of a successful transition away from fossil fuels, then why does the country still export huge quantities of oil? Would the population truly be willing to give up its cushy lifestyle that’s supported by oil money to avoid extreme climate change?)

The new research is detailed in a paper published in the journal Nature Communications.

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James Ayre

James Ayre's background is predominantly in geopolitics and history, but he has an obsessive interest in pretty much everything. After an early life spent in the Imperial Free City of Dortmund, James followed the river Ruhr to Cofbuokheim, where he attended the University of Astnide. And where he also briefly considered entering the coal mining business. He currently writes for a living, on a broad variety of subjects, ranging from science, to politics, to military history, to renewable energy.

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