Concentrations of carbon dioxide in the atmosphere in May were 50 percent higher than during the pre-industrial era, reaching levels not seen on Earth for about four million years, the main US climate agency said recently.
Global warming caused by humans, particularly through the production of electricity using fossil fuels, transport, the production of cement, or even deforestation, is responsible for the new high, the National Oceanic and Atmospheric Administration (NOAA) said.
May is usually the month with the highest carbon dioxide levels each year.
In May 2022, the threshold of 420 parts per million (ppm) -- a unit of measurement used to quantify pollution in the atmosphere -- was crossed.
In May 2021, the rate was 419 ppm, and in 2020, 417 ppm.
The measurements are taken at the Mauna Loa observatory in Hawaii, ideally located high on a volcano, which allows it to escape the possible influence of local pollution.
Before the Industrial Revolution, levels of CO2 held steady at around 280 ppm, a level maintained for approximately 6,000 years of human civilization that preceded industrialization, according to NOAA.