New research by a team at UCLA led by Aradhna Tripati has conclusively established a history of the Earth's atmospheric makeup going back 20 million years. It shows that the last time the earth had a concentration of Carbon Dioxide like today's 387 parts per million was 15 - 20 million years ago during the Miocene epoch. A time when the ancestors of modern humans were still living in trees in a world markedly different from our modern world.
ScienceDaily (Oct. 9, 2009) — You would have to go back at least 15 million years to find carbon dioxide levels on Earth as high as they are today, a UCLA scientist and colleagues report Oct. 8 in the online edition of the journal Science. The World of 15-20 million years ago was a very different kind of place.
"The last time carbon dioxide levels were apparently as high as they are today — and were sustained at those levels — global temperatures were 5 to 10 degrees Fahrenheit higher than they are today, the sea level was approximately 75 to 120 feet higher than today, there was no permanent sea ice cap in the Arctic and very little ice on Antarctica and Greenland," said the paper's lead author, Aradhna Tripati, a UCLA assistant professor in the department of Earth and space sciences and the department of atmospheric and oceanic sciences.
These aren't minor differences from our modern world. These are drastic changes from the world around us. The world we are so accustomed to.
Many of us were fascinated to read about "Ardi," who was about 4.4 million years old. To look at an earth with as much CO2 as we now have in our atmosphere we'd have to go back much much further than "Ardi", all the way back into the Miocene epoch. Large ape species evolved in Africa about 23 to 22 million years ago. About 15 million years ago a drying climate was replacing the dense forests of East Africa with savanna interspersed with areas of forest. Scientists think our ancestors came down from the trees about 7 million years ago.
More on Tripati's ground breaking study comes from PhysOrg.com
"A slightly shocking finding," Tripati said, "is that the only time in the last 20 million years that we find evidence for carbon dioxide levels similar to the modern level of 387 parts per million was 15 to 20 million years ago, when the planet was dramatically different."
Levels of carbon dioxide have varied only between 180 and 300 parts per million over the last 800,000 years — until recent decades, said Tripati, who is also a member of UCLA's Institute of Geophysics and Planetary Physics. It has been known that modern-day levels of carbon dioxide are unprecedented over the last 800,000 years, but the finding that modern levels have not been reached in the last 15 million years is new.
Tripati's research conclusively puts to rest the debate over the makeup of Earth's atmosphere before our ice core record began 800,000 ago.
By analyzing the chemistry of bubbles of ancient air trapped in Antarctic ice, scientists have been able to determine the composition of Earth's atmosphere going back as far as 800,000 years, and they have developed a good understanding of how carbon dioxide levels have varied in the atmosphere since that time. But there has been little agreement before this study on how to reconstruct carbon dioxide levels prior to 800,000 years ago.
Tripati, before joining UCLA's faculty, was part of a research team at England's University of Oxford that developed a new technique to assess carbon dioxide levels in the much more distant past — by studying the ratio of the chemical element boron to calcium in the shells of ancient single-celled marine algae.
Recent research has shown that elevated levels of CO2 will persist in the atmosphere for a many centuries to come.
"People have imagined that if we stopped emitting carbon dioxide that the climate would go back to normal in 100 years or 200 years. What we're showing here is that's not right. It's essentially an irreversible change that will last for more than a thousand years," Solomon says.
This is because the oceans are currently soaking up a lot of the planet's excess heat — and a lot of the carbon dioxide put into the air. The carbon dioxide and heat will eventually start coming out of the ocean. And that will take place for many hundreds of years.
The Oceans act as a climatic flywheel restraining the buildup of CO2 and heat in the atmosphere at first while CO2 is on the increase, but oceans also restrain decreasing CO2 and heat levels in the atmosphere when CO2 inputs decline.
We are now conducting a gigantic experiment with our planet's atmosphere.
We can't envision exactly how the results of our experiment will look, but now we can see the outlines of what is coming by looking back into time by 15 million years. A world where sea levels are at least 75 feet higher than they are now. The vision of our Miocene-like future is a sobering one indeed.