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"BY 2025, CO2 LEVELS WILL BE HIGHER THAN THEY'VE BEEN FOR THE LAST 3.3 MILLION YEARS" [Nature Scientific Reports July 10, 2020]
Let's see. What was going on 3.3 million years ago?
--Humans like us were just a gleam in evolution's eye. The most promising potential ancestor around then was Australopithecus, an apelike creature living in southern Africa who may have been the first to use shaped stones to smash open bones for their marrow.
--Earth wouldn't enter the current geologic epoch, the Holocene, for another 3,288,000 years. It was then in the middle Pliocene.
--North and South America hadn't yet collided and connected.
--North America sported two elephant-like species, hyenas, small, three-toed ancestors of modern horses, bone-crushing dogs, giant bears and three species of huge, saber-toothed cats.
--Humans wouldn't set foot on the continent for another 3.27 million years.
--Crucially, from our point of view, atmospheric CO2 levels were comparable to today's (somewhere between 381 and 427 parts per million), yet global temperatures were 2 to 3 degrees C (3.6 to 5.4 degrees F) higher than they are now, and sea levels were 25 meters (82 feet) higher.
Equally crucially, because of those nearly equal CO2 levels, the period tells us what our world may look like all too soon. "We studied this particular interval in unprecedented detail because it provides great contextual information for our current climate state," says Elwyn de la Vega, researcher at the University of Southampton's School of Ocean and Earth Science, in the UK, and lead author of the Nature Scientific Reports study.
The Southampton research team was able to pin down those ancient CO2 levels by studying the fossilized shells of foraminifera--millimeter-sized sea creatures protected by carbon-rich shells. The ratios of boron isotopes in the shells correlate with atmospheric CO2 levels at the time the shells formed.
Clearly, we're not going to see a return of saber-toothed cats or giant bears. But we, or our children or grandchildren, may well have to deal with a Pliocene climate--much hotter, lacking most of the Northern Hemisphere's ice cover, and with rapidly rising sea levels.
Why aren't we already living in mid-Pliocene conditions? Simply because there hasn't been time for the full impact of the greenhouse gases we've already pumped into the atmosphere to warm the oceans and melt most of Earth's ice. Geochemist Gavin Foster, also at the University of Southampton explains:
... it takes a while for Earth’s climate to fully equilibrate (catch up) to higher CO2 levels and, because of human emissions, CO2 levels are still climbing. Our results give us an idea of what is likely in store once the system has reached equilibrium.
To get a sense of what things will be like when Earth has reached that Pliocene-like equilibrium, picture your favorite coastal city under 80 feet of water. According to recent research, coastal flooding could displace hundreds of millions of people and cost the global economy trillions of dollars by the end of this century if we don't get a grip on climate change now.
Right now we're at 413 parts per million of atmospheric CO2, and rising, and the curve is getting steeper. We're running as fast as we can towards a very inhospitable past.
--REA
--Humans like us were just a gleam in evolution's eye. The most promising potential ancestor around then was Australopithecus, an apelike creature living in southern Africa who may have been the first to use shaped stones to smash open bones for their marrow.
--Earth wouldn't enter the current geologic epoch, the Holocene, for another 3,288,000 years. It was then in the middle Pliocene.
--North and South America hadn't yet collided and connected.
--North America sported two elephant-like species, hyenas, small, three-toed ancestors of modern horses, bone-crushing dogs, giant bears and three species of huge, saber-toothed cats.
Smilodon populator--one of North America's
Pliocene saber-toothed cats
Credit: Charles Knight/American Museum of Natural History
--Humans wouldn't set foot on the continent for another 3.27 million years.
--Crucially, from our point of view, atmospheric CO2 levels were comparable to today's (somewhere between 381 and 427 parts per million), yet global temperatures were 2 to 3 degrees C (3.6 to 5.4 degrees F) higher than they are now, and sea levels were 25 meters (82 feet) higher.
Equally crucially, because of those nearly equal CO2 levels, the period tells us what our world may look like all too soon. "We studied this particular interval in unprecedented detail because it provides great contextual information for our current climate state," says Elwyn de la Vega, researcher at the University of Southampton's School of Ocean and Earth Science, in the UK, and lead author of the Nature Scientific Reports study.
The Southampton research team was able to pin down those ancient CO2 levels by studying the fossilized shells of foraminifera--millimeter-sized sea creatures protected by carbon-rich shells. The ratios of boron isotopes in the shells correlate with atmospheric CO2 levels at the time the shells formed.
Clearly, we're not going to see a return of saber-toothed cats or giant bears. But we, or our children or grandchildren, may well have to deal with a Pliocene climate--much hotter, lacking most of the Northern Hemisphere's ice cover, and with rapidly rising sea levels.
Why aren't we already living in mid-Pliocene conditions? Simply because there hasn't been time for the full impact of the greenhouse gases we've already pumped into the atmosphere to warm the oceans and melt most of Earth's ice. Geochemist Gavin Foster, also at the University of Southampton explains:
... it takes a while for Earth’s climate to fully equilibrate (catch up) to higher CO2 levels and, because of human emissions, CO2 levels are still climbing. Our results give us an idea of what is likely in store once the system has reached equilibrium.
To get a sense of what things will be like when Earth has reached that Pliocene-like equilibrium, picture your favorite coastal city under 80 feet of water. According to recent research, coastal flooding could displace hundreds of millions of people and cost the global economy trillions of dollars by the end of this century if we don't get a grip on climate change now.
Keeling curve--atmospheric CO2 1960-2020
Credit: Scripps Research Insitute
Right now we're at 413 parts per million of atmospheric CO2, and rising, and the curve is getting steeper. We're running as fast as we can towards a very inhospitable past.
--REA
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