Earth’s carbon dioxide levels are likely the highest they've been in 15 million years

https://mashable.com/article/climate-change-carbon-pollution-15-million-years/#4qO59PgfHiqO

By Mark Kaufman
Oct. 29, 2018

Amid a backdrop of U.S. politicians still questioning whether the changing climate is attributable to humans (it is), it's quite likely that we’ve actually boosted Earth's carbon dioxide — a potent greenhouse gas — to the highest levels they’ve been in some 15 million years.

The number 15 million is dramatically higher than a statistic frequently cited by geologists and climate scientists: That today's carbon levels are the highest they've been on Earth in at least 800,000 years — as there's irrefutable proof trapped in the planet's ancient ice.

Though scientists emphasize that air bubbles preserved in ice are the gold carbon standard, there are less direct, though still quite reliable means to gauge Earth's long-ago carbon dioxide levels. These measurements, broadly called proxies, include the chemical make-up of long-dead plankton and the evidence stored in the breathing cells, or stomata, of ancient plants.

Scientists have identified this 15 million number by measuring and re-measuring proxies all over the world.

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“And there’s several lines of evidence,” Prather, a lead author on UN climate reports, added, citing the carbon dioxide evidence in fossilized marine life. “It’s not just one person’s crazy number.”

Direct measures of the air show carbon dioxide levels have recently hit 410 parts per million, or ppm, the highest-recorded number in human history.

“For the most part, carbon dioxide was below 400 ppm for the last 14 million years or so,” Matthew Lachniet, a paleoclimatologist at the University of Nevada, Las Vegas, said in an interview.

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The critical difference today, however, is that carbon emissions are expected to continue rising. With the unprecedented burning of fossil fuels, carbon accumulations will simply keep going up.

“Of course, C02 concentrations aren’t stopping today,” said Lachniet. “We’re probably going to blow through 550 to 600 ppm.”

Those sorts of high carbon concentrations haven't been experienced on Earth in well over 20 million years, noted Lachniet.

“That makes this conversation even more stark,” he said.

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Since the onset of the Industrial Revolution, Earth's average temperature has risen by 1.8 degrees Fahrenheit, or 1 degree Celsius.

Major consequences have already been regularly observed in Earth’s water cycle — bringing greater odds of extremes in deluges and drought. The most easily-predicted results, record-breaking heat waves and historic wildfires, are manifesting globally, as well as more complex atmospheric changes.

“It [global warming] raises sea levels and makes storm surges worse, it makes the atmosphere wetter, leading to flooding from extreme rainfall, and warming ocean temperatures provide extra energy to tropical storms,” climate scientist Stefan Rahmstorf, head of Earth System Analysis at the Potsdam Institute for Climate Impact Research, said in September.

"The polar ice is melting, in the ocean the Gulf Stream System is weakening, and in the atmosphere the jet stream is getting weird,” Rahmstorf added.

Unlike previous geologic epochs, the defining circumstance today isn’t just notably high carbon in the air — it’s how fast it’s all accumulating.

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“I would argue what's really relevant is where we stabilize out,” said Lachniet. “Over the next hundred years we really set the next 10,000 years of climate history.”