The data is in: carbon dioxide levels in the atmosphere hit 419 parts per million in May. The levels have now reached the dangerous milestone of being 50% higher than when the industrial age began – and the average rate of increase is faster than ever.
The figure is the highest measurement of the crucial greenhouse gas in the 63 years that data has been recorded at the Mauna Loa Atmospheric Baseline Observatory in Hawaii – despite slowdowns in air travel and industry during a global pandemic in the past year.
The 10-year average rate of increase also set a record, now up to 2.4 parts per million per year.
According to the National Oceanic and Atmospheric Administration, the reason is complex. Global emissions fell by 6.4% in 2020, but given the seasonal and natural variability, modest decreases wouldn’t make a big impact on the global tally of carbon emissions. And even as emissions dropped, wildfires burning through trees released carbon dioxide – maybe even at a similar rate as the modest lowering of emissions from the pandemic’s slowing impact on the global economy.
“The ultimate control knob on atmospheric CO2 is fossil-fuel emissions,” geochemist Ralph Keeling, whose father started gathering data at the Mauna Loa site, told NOAA. “But we still have a long way to go to halt the rise, as each year more CO2 piles up in the atmosphere. We ultimately need cuts that are much larger and sustained longer than the Covid-related shutdowns of 2020.”
In order to meet the goals of the Paris climate accords – to keep temperature rise to 1.5C – the United Nations Environment Programme report finds countries need to cut their global emissions by 7.6% every year for the next decade.
“Reaching 50% higher carbon dioxide than pre-industrial is really setting a new benchmark and not in a good way,” said Cornell University climate scientist Natalie Mahowald, who wasn’t part of the research.
“If we want to avoid the worst consequences of climate change, we need to work much harder to cut carbon dioxide emissions and right away.”
The laboratory at Mauna Loa, which sits on a volcano in the middle of the Pacific Ocean, combines two complementary observations to come up with the all-important value of carbon dioxide. The current level hasn’t existed on Earth since the Pliocene era, between 4.1m and 4.5m years ago – and global seas were 78 feet higher than current day levels.
The annual increase of 1.8 parts per million in May was slightly less than in previous years, though monthly measurements from 2021 show this year may be closer to the average increase of 2.3 parts per million.
Scientists focus on May as the month with the highest carbon dioxide levels of the year, because it comes before plants and trees in the northern hemisphere start to suck up carbon dioxide during their growing season of the summer. Then in the fall and winter, plants and soils release carbon dioxide back into the atmosphere.