Exploring Evolution Series - Mankind Enters a New Anthropocene Era

This article is from the In-Depth Report 400 PPM: What's Next for a Warming Planet

CO2 Levels for February Eclipsed Prehistoric Highs

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Global warming is headed back to the future as the CO2 level reaches a new high

March 5, 2015 |By David Biello

More and more carbon dioxide molecules are accumu-lating in Earth's atmosphere | Astronaut photograph from International Space Station, courtesy of NASA.

February is one of the first months since before months had names to boast carbon dioxide concentrations at 400 parts per million.* Such CO2 concentrations in the atmosphere have likely not been seen since at least the end of the Oligocene 23 million years ago, an 11-million-year-long epoch of gradual climate cooling that most likely saw CO2 concentrations drop from more than 1,000 ppm. Those of us alive today breathe air never tasted by any of our ancestors in the entire Homo genus.

Homo sapiens sapiens—that’s us—has subsisted for at least 200,000 years on a planet that has oscillated between 170 and 280 ppm, according to records preserved in air bubbles trapped in ice. Now our species has burned enough fossil fuels and cut down enough trees to push CO2 to 400 ppm—and soon beyond. Concentrations rise by more than two ppm per year now. Raising atmospheric concentrations of CO2 to 0.04 percent may not seem like much but it has been enough to raise the world's annual average temperature by a total of 0.8 degree Celsius so far. More warming is in store, thanks to the lag between CO2 emissions and the extra heat each molecule will trap over time, an ever-thickening blanket wrapped around the planet in effect. Partially as a result of this atmospheric change, scientists have proposed that the world has entered a new geologic epoch, dubbed the Anthropocene and marked by this climate shift, among other indicators.

We aren't done yet. Greater concentrations will be achieved, thanks to all the existingcoal-fired power plants, more than a billion cars powered by internal combustion on the roads today and yet more clearing of forests. That's despite an avowed goal to stop at 450 ppm, the number broadly (if infirmly) linked to an average temperature rise of no more than 2 degrees C. More likely, by century's end enough CO2 will have been spewed from burning long-buried stores of fossilized sunshine to raise concentrations to 550 ppm or more, enough to raise average annual temperatures by as much as 6 degrees C in the same span. That may be more climate change than human civilization can handle, along with many of the other animals and plants living on Earth, already stressed by other human encroachments. The planet will be fine though; scientists have surmised from long-term records in rock that Earth has seen levels beyond 1,000 ppm in the past.

The current high levels of CO2 have spurred calls, most recently from the National Academy of Sciences, to develop technologies to retrieve carbon from the atmosphere. The U.N. Intergovernmental Panel on Climate Change relies for that on growing plants, burning them instead of coal to produce electricity, capturing the resulting CO2 in the smokestack and burying it—or in the argot: BECCS, bioenergy with carbon capture and storage, a few examples of which are scattered around the globe. Other schemes range from artificial trees to scour the skies of excess CO2 to fertilizing the oceans with iron and having diatoms do the invisible work for us.

Climate change is inevitable and, if history is any guide to what can be expected, so, too, may be regime change. A few years of diminished rainfall and attendant bad harvests have been enough in the past to fell empires, such as in Mesopotamia orChina. The world's current roster of nations struggles to hash out a global plan to cut the pollution that causes climate change, which currently stands at 90 pages of negotiating text. In addition, one nation has submitted its individual plan (or "individual nationally determined contribution," INDC in the argot) to accomplish this feat—Switzerland.

The plans of China, the European Union and the U.S. are already broadly known, if not formally submitted. Together, they are both the biggest steps ever taken to address global warming and likely insufficient to prevent too much climate change, scientific analyses suggest. The E.U., U.S. and China remain reliant on fossil fuels and the world is slow to change that habit thus far. In fact, China has become the world's largest polluter and millions of Chinese have lifted themselves out of poverty with the power from burning more and more coal, a trick India hopes to follow in the near future.

For the Swiss, the bulk of pollution comes from driving cars and controlling the climate inside buildings. Their long-term plan is "to reduce per capita emissions to one–1.5 tonnes CO2-equivalent," the INDC states. "These unavoidable emissions will have to be eventually compensated through sinks or removals." In a world that spews more and more CO2 but needs to get to below zero emissions, bring on those sinks and removals. In the meantime the sawtooth record of rising atmospheric CO2 levels moves ever upward and March 2015 will likely be the name of the next month to boast levels above 400 ppm.

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Mass Deaths in Americas Start New CO2 Epoch

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A new proposal pegs the start of the Anthropocene to the Little Ice Age and the Columbian Exchange

March 11, 2015 |By David Biello

The atmosphere recorded the mass death, slavery and warfare that followed 1492. The death by smallpox and warfare of an estimated 50 million native Americans—as well as the enslavement of Africans to work in the newly depopulated Americas—allowed forests to grow in former farmland. By 1610, the growth of all those trees hadsucked enough carbon dioxide out of the sky to cause a drop of at least seven parts per million in atmospheric concentrations of the most prominent greenhouse gas and start a little ice age. Based on that dramatic shift, 1610 should be considered the start date of a new, proposed geologic epoch—theAnthropocene, or recent age of humanity—according to the authors of a new study.

Mass deaths after Europeans reached the Americas 

may have allowed forests to regrow, reducing atmo-

spheric concentrations of carbon dioxide and kicking

off a proposed new Anthropocene geologic epoch. | 

Courtesy of NASA

"Placing the Anthropocene at this time highlights the idea that colonialism, global trade and the desire for wealth and profits began driving Earth towards a new state," argues ecologist Simon Lewis of Leeds University and the University College of London. "We are a geological force of nature, but that power is unlike any other force of nature in that it is reflexive, and can be used, withdrawn or modified."

Lewis and Mark Maslin, a geologist at UCL, dub the decrease in atmospheric carbon dioxide the "Orbis spike," from the Latin for world, because after 1492 human civilization has progressively globalized. They make the case that human impacts on the planet have been dramatic enough to warrant formal recognition of theAnthropocene epoch and that the Orbis spike should serve as the marker of the start of this new epoch in a paper published in Nature on March 12. (Scientific American is part of Nature Publishing Group.)

The Anthropocene is not a new idea. As far back as the 18th century, the first scientific attempt to lay out a chronology of Earth's geologic history ended with a human epoch. By the 19th century, the idea was commonplace, appearing as the Anthropozoic ("human life rocks") or the "Era of Man" in geology textbooks. But by the middle of the 20th century, the idea of the Holocene—a word which means "entirely recent" in Greek and designates the most recent period in which the great glacial ice sheets receded—had come to dominate, and incorporated the idea of humans as an important element of the current epoch but not the defining one.

That idea is no longer sufficient, according to scientists ranging from geologists to climatologists. Human impacts have simply grown too large, whether it's the flood of nitrogen released into the world by the invention of the so-called Haber-Bosch process for wresting the vital nutrient from the air or the fact that civilization now moves more earth and stone than all the world's rivers put together.

Researchers have advanced an array of proposals for when this putative new epoch might have begun. Some link it to the start of the mass extinction of large mammalssuch as woolly mammoths and giant kangaroos some 50,000 years ago or the advent of agriculture around 10,000 years ago. Others say the Anthropocene is more recent, tied to the beginning of the uptick of atmospheric CO2 concentrations after the invention of an effective coal-burning steam engine.

The most prominent current proposal connects the dawn of the Anthropocene to that of the nuclear age—long-lived radionuclides leave a long-lived record in the rock. The boom in human population and consumption of everything from copper to corn after 1950 or so, known as the "Great Acceleration," roughly coincides with this nuclear marker, as does the advent of plastics and other remnants of industrial society, dubbed technofossils by Jan Zalasiewicz of the University of Leicester, the geologist in charge of the group that is advocating for incorporating the Anthropocene into the geologic time scale. The radionuclides can then serve as what geologists call a Global Stratotype Section and Point (GSSP), more commonly known as a "golden spike." Perhaps the most famous such golden spike is the thin layer of iridium found in rock exposed near El Kef, Tunisia, that tells of the asteroid impact that ended the reign of the dinosaurs and thus marked the end of the Cretaceous Period about 65 million years ago.

Lewis and Maslin reject this radionuclide spike because it is not tied to a "world-changing event," at least not yet, though it is a clear signal in the rock. On the other hand, their Orbis spike in 1610 reflects both the most recent CO2 nadir as well as the redistribution of plants and animals around the world around that time, a literal changing of the world.

Much like the golden spike that marks the end of the dinosaurs, the proposed Orbis spike itself would be tied to the low point of atmospheric CO2 concentrations around 1610, as recorded in ice cores, where tiny trapped bubbles betray past atmospheres. Further geologic evidence will come from the appearance of corn pollen in sediment cores taken in Europe and Asia at that time, among other indicators that will complement the CO2 record. Therefore, scientists looking at ice cores, mud or even rock will find this epochal shift in the future.

The CO2 drop coincides with what climatologists call the Little Ice Age. That cooling event may have been tied to regenerated forests and other plants growing on some 50 million hectares of land abandoned by humans after the mass death brought on by disease and warfare, Lewis and Maslin suggest. And it wasn't just the death of millions of Americans, as many as three-quarters of the entire population of two continents. The enslavement (or death) of as many as 28 million Africans for labor in the new lands also may have added to the climate impact. The population of the regions of northwestern Africa most affected by the slave trade did not begin to recover until the end of the 19th century. In other words, from 1600 to 1900 or so swathes of that region may have been regrowing forest, enough to draw down CO2, just like the regrowth of the Amazon and the great North American woods, though this hypothesis remains in some dispute.

Whether in 1610, 1944 or 50,000 B.C., the new designation would mean we are living in a new Anthropocene epoch, part of the Quaternary Period, which started more 2.5 million years ago with the advent of the cyclical growth and retreat of massive glaciers. The Quaternary is part of the Cenozoic, or "recent life," Era, which began 66 million years ago, which is, in turn, part of the Phanerozoic ("revealed life") Eon, which started 541 million years ago and encompasses all of complex life that has ever lived on this planet. In the end, the Anthropocene might supplant its old rival the Holocene. "It is only designated an epoch, when other interglacials are not, because back in the 18th century geologists thought humans were a very recent species, arriving via divine intervention or evolving on Earth in the Holocene," Lewis argues, but scientists now know Homo sapiens arose more than 200,000 years ago in the Pleistocene epoch. "Humans are a Pleistocene species, so the reason for calling the Holocene an epoch is a relic of the past."

Maslin suggests downgrading the Holocene to a stage within the Pleistocene, like other interglacial spans in the geologic record. But Zalasiewicz disagrees with this bid to get rid of the Holocene. "I don't see the need," he says. "Systematic tracing of a Holocene / Anthropocene boundary globally would be a very illuminating process in all sorts of ways."

The changes wrought by humans over the course of the last several centuries, if not longer, will echo in the future, whether in the form of transplanted species, like earthworms or cats, crop pollen in lake sediments or even entire fossilized cities. Still, whether the Anthropocene started tens, hundreds or thousands of years ago, it accounts for a minute fraction of Earth's history. And this new epoch could end quickly or endure through millennia, depending on the choices our species makes now. "Embracing the Anthropocene reverses 500 years of scientific discoveries that have made humans more and more insignificant," Maslin notes. "We argue that Homo sapiens are central to the future of the only place where life is known to exist."