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CO2 in the atmosphere was just below 421 parts per million (ppm) for May 2022, the highest monthly average since records began in the late 1950s. The data was measured at the Mauna Loa Observatory in Hawaii, which has the longest continuous record of atmospheric CO2 on Earth.
CO2 typically peaks in May each year, and last year’s record reached just over 410ppm. In May 1958, the first year on record, atmospheric CO2 was around 310ppm.
CO2 is one of the major greenhouse gases warming the planet and contributing to the climate crisis. Levels have increased dramatically since the start of the Industrial Revolution in the 19th century due to the burning of fossil fuels, as well as such practices as deforestation and agriculture.
Warmer temperatures are melting ice sheets, raising sea levels, strengthening storms and contributing to droughts around the world. In addition, higher CO2 levels in the atmosphere risk making ocean water more acidic, potentially devastating some marine life.
The consequences of these changes put everything from food security and human health to built infrastructure at risk around the world, according to the most recent report from the Intergovernmental Panel on Climate Change (IPCC), the leading global authority on climate science.
This year, the IPCC warned that global greenhouse gas emissions needed to start declining by 2025 – three years from now – to keep the world at around 1.5C of warming. With every bit of further warming, droughts, heatwaves and storms are all likely to get both more frequent and more intense, it notes.
Before the 19th century, CO2 levels hovered at around 280ppm for around 6,000 years, the NOAA notes. The last time levels were this high, more than four million years ago, sea levels were somewhere between five and 25 metres (16-82 feet) higher than they are now, the agency adds.
The previous record was reached this April as average monthly levels crept over 420ppm for the first time on record.
CO2 usually peaks in May since most of the planet’s land is in the northern hemisphere and warm summers spur plant growth that temporarily draws carbon out of the atmosphere through photosynthesis.