The main US climate agency reported Friday that carbon dioxide concentrations in the atmosphere reached levels not seen on Earth for nearly 4 million years in May, 50 percent higher than during the pre-industrial era.
According to the National Oceanic and Atmospheric Administration (NOAA), global warming caused by human activities, especially electricity production using fossil fuels, transport, cement production, or even deforestation, is responsible for the new record.
Carbon dioxide levels are usually highest in May each year.
The threshold of 420 parts per million (ppm) - a unit of measurement used to measure pollution levels in the atmosphere - was crossed in May 2022.
In May 2021, the rate was 419 parts per million, and in 2020, 417 parts per million.
Hawaii's Mauna Loa Observatory, located high on a volcano, is ideally located to minimise the effects of local pollution.
Prior to the Industrial Revolution, CO2 levels were steady at around 280 parts per million, a level sustained for approximately 6,000 years of human civilization.
CO2 levels are now comparable to what they were 4.1 to 4.5 million years ago when CO2 levels were near or above 400 ppm, the agency said in a statement.
The sea level was five to twenty-five meters higher at that time, enough to submerge many of today's major cities. The Arctic was also covered in large forests at that time.
Global warming is caused by greenhouse gases such as CO2. These gases remain in the atmosphere and oceans for thousands of years.
As a result of its warming effect, NOAA reported, heat waves, droughts, fires, and flooding are already becoming more frequent.
Pieter Tans, a scientist with the Global Monitoring Laboratory, said carbon dioxide is at levels our species has never seen before.
"We have known about this for half a century, and have failed to do anything meaningful about it. What's it going to take for us to wake up?"
What do we have to do to wake up?