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Human Ancestors Evolved in a Low-Carbon World
By Tim Radford
For the entire 2.5 million years of the Ice Age epoch called the Pleistocene, it was a low-carbon world. Atmospheric carbon dioxide hovered around 230 parts per million. Not only did Homo sapiens evolve on a low-carbon planet, so did Homo erectus and most other human species now known only from fossil evidence in Europe and Asia.
And this long history of a planet kept cool and stable by low levels of greenhouse gas in the atmosphere continued long after the discovery of fire, the Stone Age, the Bronze Age, the Iron Age, the fall and rise of empires and the Industrial Revolution.
Only in 1965 did carbon dioxide levels pass 320 ppm, after a century of exploitation of fossil fuels that released ancient carbon back into atmospheric circulation.
By 2019, the carbon dioxide concentration in the atmosphere had tipped 410 ppm and is still rising. In less than a century, human action had raised planetary average temperatures by around 1°C. At present rates, this average could reach 3°C by the end of this century.
Researchers have known for a century that humans emerged in a cooler world, but much of the story of the distant past was based on the evidence of fossils and sedimentary rocks. The latest research pushes the detailed atmospheric carbon dioxide accounting back to at least 2.5 million years.
Researchers report in the journal Nature Communications that they studied the pattern of carbon isotope readings preserved in the deep yellow soils of China's Loess Plateau. What they found confirmed 800,000 years of annual evidence from the ice cores of Antarctica and Greenland – and far beyond that limit.
The wind-blown Loess of China dates back to at least 22 million years and each successive layer carries isotope evidence that can be read as testimony to the atmospheric conditions in which the soils were laid down.
The latest find confirms that the normal state of the planet during human evolution was cool, with low levels of atmospheric carbon. Homo erectus was the first known human predecessor to exploit fire, systematically fashion stone hand axes, and to leave Africa for Asia and Europe.
"According to this research, from the first Homo erectus, which is currently dated to 2.1 to 1.8 million years ago, we have lived in a low-carbon environment – concentrations were less than 320 parts per million," said Yige Zhang, a geoscientist at Texas A&M University in the U.S., who worked with colleagues in Nanjing, China and the California Institute of Technology.
"So this current high carbon dioxide experiment is not only an experiment for the climate and the environment – it's an experiment for us, for ourselves."
"This is definitely further evidence that fossil fuels and anthropogenic activity actually has fundamentally changed the climate." In my 1st @EcoWatch post today, studies show the speed and scope of the #ClimateCrisis is unique in the last 2,000 years: https://t.co/SdL04YZStu— Olivia Rosane (@orosane) July 25, 2019
Reposted with permission from our media associate Climate News Network.
EcoWatch Daily Newsletter
By Pedro Biondi
Extinct in its habitat for at least three decades, the Alagoas curassow (Pauxi mitu) is now back in the jungle and facing a test of survival, thanks to the joint efforts of more than a dozen institutions to pull this pheasant-like bird back from the brink.
By Julia Conley
Sen. Elizabeth Warren expanded her vision for combating the climate crisis on Tuesday with the release of her Blue New Deal — a new component of the Green New Deal focusing on protecting and restoring the world's oceans after decades of pollution and industry-caused warming.
A judge in New York's Supreme Court sided with Exxon in a case that accused the fossil fuel giant of lying to investors about the true cost of the climate crisis. The judge did not absolve Exxon from its contribution to the climate crisis, but insisted that New York State failed to prove that the company intentionally defrauded investors, as NPR reported.
By Sharon Elber
You may have heard that giving a pet for Christmas is just a bad idea. Although many people believe this myth, according to the ASPCA, 86 percent of adopted pets given as gifts stay in their new homes. These success rates are actually slightly higher than average adoption/rehoming rates. So, if done well, giving an adopted pet as a Christmas gift can work out.