Carbon dioxide in Earth's atmosphere has set another ominous record

November 25, 2019, 12:58 p.m.
side view of Earth's atmosphere from orbit
Photo: NASA Jet Propulsion Laboratory

Change is in the air, or at least the air itself is changing. Earth's atmosphere is shifting to a state unseen in human history, and according to a new report from the World Meteorological Organization (WMO), it just reached another record high.

Our atmosphere held a global average of 407.8 parts per million (ppm) of carbon dioxide (CO2) in 2018, compared with 405.5 ppm in 2017, the WMO announced today in its annual Greenhouse Gas Bulletin. That increase is slightly above the average yearly uptick over the last decade, according to the WMO, which notes CO2 remains in the sky for centuries, and in the ocean for even longer.

Levels of methane and nitrous oxide also surged by higher amounts in 2018 than the yearly average over the past decade, the WMO adds, and since 1990, there has been a 43% overall increase in radiative forcing (the climate's warming effect) caused by long-lived greenhouse gases. About 80% of that increase is due to CO2, the WMO notes, and there are "multiple indications that the increase in the atmospheric levels of CO2 are related to fossil fuel combustion."

For example, fossil fuels like coal, oil and natural gas were created from plant material millions of years ago, the WMO explains, and do not contain radiocarbon. "Thus, burning it will add to the atmosphere radiocarbon-free CO2, increasing CO2 levels and decreasing its radiocarbon content. And this is exactly what is demonstrated by the measurements."

Earth's air always has some CO2, which plants need for photosynthesis, but too much creates the heat-trapping effect responsible for climate change. Global CO2 levels naturally fluctuate by season due to plant growth, falling in the Northern Hemisphere's summer and rising in winter. That cycle continues, but with more and more CO2 due to the rampant burning of fossil fuels.

clouds around Mauna Loa Observatory in Hawaii Clouds undulate around Hawaii's Mauna Loa Observatory, where scientists keep track of CO2 levels in Earth's atmosphere. (Photo: LCDR Eric Johnson [CC BY 2.0]/NOAA)

On May 9, 2013, CO2 levels at Mauna Loa Observatory in Hawaii reached 400 ppm for the first time since the Pliocene Epoch, which ended about 2.8 million years before modern humans existed. (Natural phenomena raised Pliocene CO2 levels gradually, while humans are raising current levels extremely quickly by climatic standards — and with no precedent for how it will affect our species.) CO2 levels fell back to the 390s in the summer of 2013, but not for long. They were above 400 again by March 2014, and Mauna Loa's entire monthly average broke 400 ppm that April. Then, in 2015, the global yearly average surpassed 400 ppm for the first time. It was up to 403 ppm in 2016, 405 in 2017 and now we know it averaged nearly 408 ppm in 2018.

"It is worth recalling that the last time the Earth experienced a comparable concentration of CO2 was 3-5 million years ago," said WMO Secretary-General Petteri Taalas in a statement, referring to the Pliocene. "Back then, the temperature was 2-3°C (3.6 to 5.4 degrees Fahrenheit) warmer, sea level was 10-20 meters (33 to 66 feet) higher than now."

It's already too late to stop some effects of human-induced climate change, and the situation continues to worsen every day. Still, however, it's also way too early to give up, both for our own sake and for that of future generations.

"There is no sign of a slowdown, let alone a decline, in greenhouse gases' concentration in the atmosphere despite all the commitments under the Paris Agreement on Climate Change," Taalas added. "We need to translate the commitments into action and increase the level of ambition for the sake of the future welfare of mankind."

While the Paris Agreement marked an important step forward in the global effort to rein in greenhouse gas emissions, this WMO report is the latest warning that bigger steps are still needed. That will be the challenge next month in Madrid, where negotiators and world leaders will convene for U.N. climate talks from Dec. 2-15.

Editor's note: This article has been updated with new information since it was originally published in September 2016.