Atmospheric carbon dioxide hit a monthly average of 419 parts per million in May 2021, according to data from NOAA and the Scripps Institution of Oceanography released Monday.
"We are adding roughly 40 billion metric tons of CO2 pollution to the atmosphere per year," Peter Tans, senior scientist with NOAA's global monitoring lab, said in a statement.
"That is a mountain of carbon that we dig up out of the Earth, burn and release into the atmosphere as CO2 -- year after year. If we want to avoid catastrophic climate change, the highest priority must be to reduce CO2 pollution to zero at the earliest possible date."
Carbon dioxide is the most abundant greenhouse gas in the atmosphere, it is added from activities like burning fossil fuels to generate electricity, burning oil for transportation, industrial activity like manufacturing, agriculture and deforestation according to NOAA.
Carbon dioxide and other greenhouse gases trap heat in the atmosphere, leading to increasing average temperatures and consequences like rising sea levels, ocean acidification and decreasing amounts of Arctic sea ice.
May is typically the highest CO2 measurement of the year as spring and summer in the northern hemisphere means more plants start to remove CO2 from the atmosphere in the following months.