The concentration of carbon dioxide in the atmosphere reached its highest level recorded by modern instruments in April, and is expected to rise even further this month, according to scientists.
The month of May was forecast to set a new record for CO₂ levels, said Pieter Tans, senior scientist at the National Oceanographic and Atmospheric Administration.
“It is very concerning, extremely worrisome,” he said. Not only were carbon dioxide levels high, they were also rising faster and faster, he said.
“This last decade, the rate of increase has never been higher, and we are still on the same path,” said Tans. “So we are going in the wrong direction, at maximum speed.”
Carbon dioxide is the primary driver of global warming and it can remain in the atmosphere for hundreds of years.
During the year, CO₂ levels fluctuate as vegetation grows in the spring, and then decomposes — a cycle referred to as the “breathing” of the earth, which is shown in the wiggles on the carbon dioxide charts (above).
As a result of this annual cycle, CO₂ levels typically peak during each April and May, when the large amount of vegetation in the northern hemisphere is releasing carbon dioxide.
The longest continuous source of modern CO₂ records comes from Mauna Loa, a volcanic island in Hawaii, where geochemist Charles Keeling started measurements in 1958.
The Mauna Loa data, also known as the “Keeling Curve” (visible as the grey wiggly line in the chart above) are considered one of the most definitive proofs of human impact on the planet.
Overall concentrations of carbon dioxide in the atmosphere have surged in recent decades, contributing to global warming of around 1.1C, compared with pre-industrial times.
“That is the signature of all our human activities, primarily burning fossil fuels all over the planet,” says Tim Lenton, professor of climate change at the University of Exeter.
“Global warming is doing all kinds of things already to the planet, it has certainly changed the frequency and intensity of some extreme weather events,” said Lenton, pointing to phenomena such as heatwaves, forest fires, and the gradual rise of the sea levels.
In 2021, emissions of carbon dioxide from energy sources rose to a record high, as the global economy recovered from the pandemic.
The planet itself typically absorbs about half of that carbon dioxide in the ocean and in vegetation. The remainder stays in the atmosphere, however, resulting in the rising concentrations of CO₂.
Recent research shows that global warming may also be changing the planet’s ability to absorb carbon dioxide.
Monitoring of CO₂ concentrations has indicated that the extent of the seasonal change, or amplitude, is increasing. This suggested that the planet was absorbing and releasing larger amounts of CO₂ than before, said Penelope Pickers, research fellow at the University of East Anglia.
The trend of rising CO₂ concentrations suggests it will be even harder to hit the targets laid out in the Paris climate accord, which aims to limit global warming to well below 2C, and ideally to 1.5C.
“It is disconcerting when we see that CO₂ is constantly rising,” said Pickers. “Because it is a reminder of this time that is running out.”