Carbon dioxide expected to reach at levels last witnessed during Pliocene Epoch. On Earth, the concentration of carbon dioxide in the air reached 400 parts per million (ppm) for the first time in human history.
The last time more than 3 million years ago when the planet experienced such high levels of the greenhouse gas, the conditions on Earth were unrecognizable from what is now and giant camels roamed a mostly ice-free High Arctic.
In 2020 scientists are forecasting that atmospheric carbon dioxide concentrations will likely peak at around 417 ppm, which means for every 1 million molecules of gas in the atmosphere, 417 are carbon dioxide. Once what was an alarming threshold has now become business as usual, and with that, humanity will be charging into an uncharted territory completely.
“For millions of years, we haven’t had an atmosphere with a chemical composition as it is right now,” said Martin Siegert, co-director of the Grantham Institute at Imperial College London.
The carbon dioxide concentration is simply an indicator of how humans are influencing the climate on Earth. Carbon dioxide and other greenhouse gases released from the burning of fossil fuels trap heat in the atmosphere. Elevated concentrations of carbon dioxide result in higher global temperatures, melting ice, and rising seas, among other effects of climate change.
The rise in atmospheric carbon dioxide is expected to be higher by 10 percent than usual this year, according to University of Exeter geography professor Richard Betts, head of the climate impacts division at the Meteorological Office, the U.K.’s national weather service. Australia’s devastating wildfire season will contribute to about 1 percent to 2 percent of the increase, he added.
The historic fires of Australia that burnt at a stretch from September to early February are thought to have unleashed about 900 million tons of carbon dioxide into the atmosphere.
Earth was amid the Pliocene Epoch when the planet last had an atmosphere like today’s chemical buildup, and that geologic period lasted from about 5.3 million to 2.6 million years ago. At that period, humans had yet to appear on the planet, and average sea levels were up to 65 feet higher than they currently are. Global average temperatures were around 7 degrees Fahrenheit more than now, and warmth at the poles was double, according to Siegert.
“There would have been a lot less ice on the planet — there probably wasn’t a Greenland Ice Sheet, the West Antarctic Ice Sheet had probably melted, and big chunks of the East Antarctic Ice Sheet had probably de-glaciated, as well,” he said.
Since 1958, carbon dioxide levels had jumped about 100 ppm, when the American scientist Charles David Keeling first started recording daily atmospheric measurements using instruments at the Mauna Loa Observatory in Hawaii. According to an unpublished working paper by Siegert and his colleagues at the Grantham Institute, a similar increase took 10,000 years, from the coldest part of the last ice age to its end.
This year’s forecasts from the U.K.’s Met Office say atmospheric carbon dioxide concentrations are expected to soar to 417 ppm. As per Siegert, this rapid rate of change is “deeply concerning.”
“We’ve done in a little more than 50 years what the Earth naturally took 10,000 years to do,” he said.
Carbon dioxide levels that are usually depicted on a graph are known as the Keeling Curve, named after Keeling, who died in 2005. The iconic graph shows that carbon dioxide levels are increasing over time and also at a continuously faster pace in recent years. The impact of human-caused climate change is apparent from the graph’s steep incline, which was already evident by the 1960s.
The Keeling Curve appears as a jagged line within the graph’s overall upward swing, and apart from registering a peak each year, a trough is there to match the natural fluctuations in Earth’s so-called carbon cycle.
As per the carbon cycle, the planet tries to regulate its temperature by naturally storing and exchanging carbon among the atmosphere, land, oceans, rocks, and living organisms like an intricate symphony.
“In the spring and summer, as vegetation greens, this helps draw down carbon dioxide from the atmosphere,” Betts said. “In the fall and winter, carbon dioxide is released back into the atmosphere when plants die and trees shed leaves.”
In early spring, atmospheric carbon dioxide usually peaks just before the forest regrowth that helps offset a part of greenhouse gas emissions.
The human-induced changes, such as burning fossil fuels or mass deforestation, not only overwhelm the natural carbon cycle but also outpace the ability of the planet to offset elevated greenhouse gases.
Betts said the pace of change has been sobering to witness.
“The rate of rise in the last decade has been faster than previous decades,” he said. “We’re just tracking ever onwards, and 400 ppm is now a distant memory.”
Ralph Keeling, a professor of geochemistry at the Scripps Institution of Oceanography and the son of Charles David Keeling, said significantly cutting down fossil fuel emissions can only halt the trajectory of the Keeling Curve.
“As long as [carbon dioxide] keeps rising, each year’s peak will exceed the peak from the previous year,” he told NBC News in an email. “We expect the peak this year to be just above 417 ppm. It looks like we are on pace to easily reach that high.”
Even if the statistics are painting a bleak picture, Siegert said he is hopeful for the actions of young environmentalists who understand what’s at stake in the climate crisis and demanding change.
“They get it in a way that decision-makers right now don’t,” he said, “so I’m optimistic, because I think, in the next 30 years, we’ll be in good hands.”