The concentration of the heat-trapping gas topped 420 parts per million, while the planet has warmed more than two degrees.
By Jason Samenow
When the station began collecting CO2 measurements in the late 1950s, atmospheric CO2 concentration sat at around 315 parts per million. On Saturday, the daily average was pegged at 421.21 parts per million — the first time in human history that number has been so high. Previously, it had never exceeded 420 parts per million.
“We’re completely certain that the increase in CO2 is warming the planet,” wrote Kate Marvel, an associate research scientist at Columbia University, in an email. “I’m even more certain CO2 causes global heating than I am that smoking causes cancer. The world is already more than 2 [degrees F] warmer than it was before the Industrial Revolution.”
In addition to the temperature increase, a warmer atmosphere supports more instances of drought in some areas and flooding rains in others, along with stronger hurricanes and typhoons and the potential for more storms to rapidly intensify in dangerous, unpredictable ways.
Halfway to doubling preindustrial CO2
Carbon dioxide emissions are a product of electricity production, transportation and industry. The United States alone emits more than five billion metric tons of CO2 annually — the weight of 13.2 million fully loaded Boeing 747s, or roughly68,000 Washington monuments.
About half of emitted CO2 remains in the atmosphere and induces warming, while more than a quarter is absorbed into the oceans, where it acidifies the water and disrupts marine ecosystems.
There is special significance in reaching and surpassing a concentration of 416 part per million. It means we’ve passed the midpoint between preindustrial CO2 levels of around 278 parts per million, and a doubling of that figure, or 556 parts per million.
The record of 421 parts per million reached Saturday is just a single point and occurred when CO2 levels are nearing their yearly peak. But the levels over the past two months over 417 parts per million signal that the annual average concentration is likely to exceed 416 parts per million.
“Although ‘halfway to doubled CO2’ is not of any physical significance, it can nevertheless be considered a milestone that highlights how much humans have already altered the composition of the global atmosphere and increased the amount of a gas that warms the global climate,” wrote the U.K. Met Office.
What a doubling of CO2 means
The anticipated doubling of atmospheric CO2, which is likely by the year 2060, has been connected to a predicted 3-degree or greater warming of the planet.
A study released last year found doubling CO2 levels will likely lead to a temperature rise between 4.1 and 8.1 degrees Fahrenheit (2.3 and 4.5 degrees Celsius), ruling out more modest warming scenarios.
Even if greenhouse gas emissions were to plummet overnight, the planet would continue warming for years to come.
“CO2 accumulates in the atmosphere,” wrote Zeke Hausfather, a climate scientist at the Breakthrough Institute in California, in an email. “The amount of warming that the world is experiencing is a result of all of our emissions since the industrial revolution — not just our emissions in the last year.”
He noted that’s why CO2 levels at Mauna Loa continued climbing and reaching new records despite a brief dramatic reduction in global emissions stemming from the covid-19 pandemic. Emissions have since returned to near pre-pandemic levels.
Data obtained from glacial ice cores indicates that modern-day CO2 levels are higher than during any point in at least the past 800,000 years.
Worrying trends with other greenhouse gases
Methane, also a significant driver of the warming climate, has shown a “huge and unprecedented increase” too, wrote to the British Antarctic Survey. Agriculture, specifically the raising of livestock and manure management, are primary sources of methane in the United States, followed by petroleum and natural gas production, as well as a coal mining and landfills.
Carbon dioxide is roughly eight times more abundant in the Earth’s atmosphere, but methane is more effective at heating the atmosphere.
Sulfur hexafluoride, a greenhouse gas that results from the production of insulators used on electrical grids, also reached all-time records of 10 parts per trillion. While its concentration remains orders of magnitude more dilute than that of most other major greenhouse gases, its rate of increase in the atmosphere has doubled since 2003.
Sulfur hexafluoride is also thousands of times more potent — a single molecule can cause 23,900 times more warming than a molecule of CO2. And a single molecule of sulfur hexafluoride can stick around in the atmosphere for more than three millennia.
At the midpoint toward doubling CO2 levels, the planet has already warmed more than 2 degrees (1 to 1.5 degrees Celsius). Last year rivaled the planet’s hottest year in modern records.
The World Meteorological Organization recently said there is at least a 1 in 5 chance of the global average temperature temporarily exceeding 2.4 degrees (1.5 Celsius) by 2024, which the Paris climate accord sets out to avoid.
At a speech at Columbia University in December, U.N. Secretary General António Guterres said nations need to cut emissions by at least six percent annually through 2030 to avoid surpassing this 1.5-degree threshold.
“We can’t avoid climate change — it’s already here,” wrote NASA’s Marvel. But “it’s still possible to escape the worst with smart policy that recognizes the scale of the threat and the need for quick action.”