At a Glance

The current CO2 concentration of 410 ppm is unprecedented over the past 3 million years.Changes in CO2 concentrations dramatically affected how long glaciers covered the Northern Hemisphere.The study also showed the planet is extremely sensitive to small changes in CO2 levels.

The Earth’s atmosphere likely contains more carbon dioxide today than at any time in at least 3 million years, according to advanced computer modeling.

The research, published in the journal Science Advances, also suggests the to relatively small variations in atmospheric CO2.

Matteo Willeit, a postdoctoral climate researcher at the Potsdam Institute for Climate Impact Research, and his team examined climate changes from about 2.59 million years ago to the present, a span known as the Quaternary period.

"It seems we're now experienced during the entire current geological period, the Quaternary," Willeit said in a statement accompanying the study's publication. "A period that started almost 3 million years ago and saw human civilization beginning only 11,000 years ago. So, the modern climate change we see is big, really big; even by standards of Earth history."

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The Quarternary has been marked by the appearance and disappearance of glaciers spreading over the Northern Hemisphere. These giant ice sheets. About 1 million years ago, however, the cycle switched to every 100,000 years.

The start of the glacial cycles from cold to warm and back was mainly triggered by a decrease of CO2 levels, Willeit's team found. Among the potential causes are increased chemical weathering (erosion of rocks), enhanced CO2 burial in deep-sea sediments, and decreased outgassing from volcanoes.

"We know from the analysis of sediments on the bottom of our seas about past ocean temperatures and ice volumes, but so far the role of CO2 changes in shaping the glacial cycles has not been fully understood," Willeit said. "It is a breakthrough that we can now show in computer simulations that changes in CO2 levels were a main driver of the ice ages, together with variations of how the Earth orbits around the sun, the so-called Milankovitch cycles."

The computer simulation looked at changes in the Earth's orbit and changes in sediment distribution on the planet's surface. It took into account how much dust was in the atmosphere — more dust means darker ice that melts quicker. And it examined different scenarios for how much CO2 volcanoes were producing.

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The model found two things, in addition to the orbital changes, had to occur for the glacial cycle length to increase from 41,000 years to 100,000 years. CO2 in the atmosphere had to decline, which made the climate cooler. And the ice sheets had to push away a layer of ground-up rock, called regolith, to expose bedrock. The bedrock gave the glaciers a better place to anchor so they could , according to a Live Science report, and therefore, last longer.

A section of glacier is seen from NASA's Operation IceBridge research aircraft along the Upper Baffin Bay coast on March 27, 2017, above Greenland. Greenland's ice sheet is retreating due to warming temperatures. Scientists say the Arctic has been one of the regions hardest hit by climate change.

(Mario Tama/Getty Images)

The simulation also suggested the global temperature never exceeded the average preindustrial temperature by more than 3.6 degrees Fahrenheit (2 degrees Celsius) during the Quaternary period. The ice sheets could never have formed 3 million years ago, Willeit wrote in a blog post.

The model showed the average global temperatures were temporarily about 2.7 degrees Fahrenheit (1.5 degree Celsius) higher than the preindustrial average about 2.5 million years ago.

Earth's temperature already is 2.1 degrees F (1.2 degrees C) warmer than the preindustrial average. The goal of the 2016 Paris Agreement is "to keep a global temperature rise this century (3.6 F) and to drive efforts to limit the temperature increase even further to 1.5 degrees Celsius (2.7 F) above preindustrial levels."

Carbon dioxide had decreased to below about 350 parts per million at the start of the ice sheet growth, Willeit wrote. The computer model suggests CO2 was below 400 ppm for the entire Quaternary period.

"Our results indicate that the current CO2 concentration of about 410 ppm is unprecedented over the past 3 million years," he said.

In the context of future climate change, the study said, "a failure in substantially reducing CO2 emissions to comply with the Paris Agreement target of limiting global warming well below 2 degrees C (3.6 F) will not only bring Earth’s climate away from Holocene-like conditions but also push it beyond climatic conditions experienced during the entire current geological period."