What was the Earth like last time CO2 levels were as high as today

is a Mashable series that answers provocative and prominent questions about the Earth’s warming climate.

Last time CO2 levels were as high as today, ocean waters, where there are now metropolises like Houston, Miami and New York.

There is a time called Pliocene or mid-Pliocene, when sea levels were (but) and. The Pliocene was a significantly warmer world, probably at about 5 degrees Fahrenheit (about 3 degrees Celsius) warmer than pre-industrial temperatures of the late 1800s. Much of the Arctic, which today is mostly covered in ice, has melted. Heat-capturing carbon dioxide levels, main temperature, hovered around 400 parts per million, or ppm. Today these levels are similar but constantly growing .

Mankind will reach Pliocene temperatures by the end of the century – unless nations in the coming decades. Sea level, of course, is not going to rise by tens of feet: Mile-thick ice sheets take many centuries to thousands of years to melt. But, importantly, humanity is already preparing the stage for a relatively rapid return to Pliocene climates, or climates at least significantly warmer than they are now. It happens fast. When CO2 nature increases in the atmosphere, pockets of ancient air show that this rise in CO2 occurs gradually, over thousands of years. But today, carbon dioxide levels are exploding as people burn long-buried fossil fuels.

“CO2 in the atmosphere has grown 100 ppm in my life,” said Kathleen Benison, a geologist at the University of West Virginia who is researching past climates. “That’s incredibly fast geologically.”

“You don’t have to be a scientist to realize that something completely strange is happening, and that strange thing is humans,” remarked Dan Lunt, a climate scientist at the University of Bristol who researched the Pliocene.

A 2013 NASA chart showing the Earth’s atmospheric CO2 levels has already reached levels similar to the Pliocene.

The problem Pliocene

Of course, it takes a long time for sea level to reach global warming. But in many other ways, the planet has been reacting to about 2 F (1.1 C) of warming since the end of the 1800 ::, warming worlds are, and beyond.

More warming will aggravate these consequences of increased heat. It will get worse. But will it get worse? That depends on the: people.

“CO2 levels will rise,” Lunt said. “We could hit the Pliocene in terms of temperature. But it depends on how fast we emit [greenhouse gases]. “

“CO2 levels will rise.”

Some of the human movements taking place on Earth today will not be reversed for centuries or thousands of years. Mostly this is because civilization enters the atmosphere every year, and all these heat-trapping gases will not magically disappear from the air, even if we immediately stop adding carbon to the atmosphere. Rather, they will have effects on the planet – like gradually rising seas and – for at least centuries. Already sea levels since the late 1800s, and a conservative assessment, by the UN Intergovernmental Panel on Climate Change, is that sea levels will rise by the end of the century. But this could very well be more than two or three feet, or even more depending on what the Antarctic colossal, melting Glacier Thwaites (it’s the size of Britain).

“Sea level rise and ocean acidification are constant on a human time scale,” said Julie Brigham-Grette, a geologist at the University of Massachusetts Amherst, who is researching how the Arctic has changed since the Pliocene.

Explosive atmospheric CO2 levels in the last century.

Explosive atmospheric CO2 levels in the last century.

The Pliocene certainly cannot give us all the answers about our direction. We do not know, for example, how quickly the seas rose during this distant period. But the Pliocene does show us how sensitive parts of the Earth are to only a few degrees of warming. For example, much of the vast Greenland ice sheet, which is twice and twice as large as Texas, melted during the warmer Pliocene. And ancient ones, dated to the Pliocene, show where past coasts lay: a stadium 30 feet taller than today is ominous.

“That means the ice sheets are really sensitive to modest warming,” said Rob DeConto, a professor of climatology at Amherst University in Massachusetts who studies the response of ice creams to a warming climate.

This does not bode well for a human civilization that inhabits the coasts much. “There civilization has built much of its infrastructure,” DeConto said. “We’re a species that gravitated to the coast.”

Pliocene heat

Earth’s CO2 levels have always fluctuated naturally. Humans did not exist (and would not have existed for millions of years) during the Pliocene – although our hairy primate ancestors were at the time.

So what explains the high Pliocene CO2 levels (400 ppm) without a world of fuel cars and coal-fired power plants? The answer lies in deep time.

Long before the Pliocene, CO2 levels were extremely high during the time of the dinosaurs (which ended 65 million years ago), possibly in some. Terrible CO2 emissions, from incessant and extreme volcanism, warmed the Earth and allowed dinosaurs to roam in suffocating Antarctica. But over millions of years, the Earth’s natural processes (specifically the slow, grinding, but powerful, called “the rock thermostat”) gradually reduced CO2 levels to about 400 ppm during the Pliocene. (We know this because there are indirect ways to measure the Earth’s CO2 levels from millions of years ago, including the chemical composition of long-dead plankton and the evidence stored in the breathing cells, or stomata, of ancient plants.)

“We’re on our way to the Pliocene.”

After the Pliocene, the Earth continued to draw CO2 from the air, eventually setting CO2 levels during the more recent ice ages, when mammoths, mastodons, and giant sloths ruled cooler land, and humans finally emerged. But humanity, by rapidly excavating and burning fossil fuels, has now promptly returned CO2 to Pliocene levels.

“We, in 150 years, have completely reversed everything the‘ rock thermostat ’has done in the last 3 million years,” Brigham-Grette explained. “The transition from warm Arctic to cold, which has icy streets, has taken a million years. We’ve jumped out of that in less than 150 years.”

Indeed, the Arctic has changed dramatically in just the last 40 years. . The merger of Greenland is.

Mankind, fortunately, still has the ability to stabilize Earth’s temperatures this century at levels that would like more extreme storms, coral destruction, punishing heat and more. But, now, we are on a trajectory to the climates of 3 million years ago. (And in a sense – especially atmospheric CO2 – we’re already there.)

“We’re on our way to the Pliocene,” Brigham-Grette said.