Counting on … day 

19th February 2024

Carbon dioxide – parts per million

The concentration of carbon dioxide is measured as so many ‘parts per million’. Measurements of carbon dioxide are made at the Mauna Loa Observatory, Hawaii (NOAA). Recordings there first began in 1958. 

Pre industrial levels of CO2 were fairly constant (for at least 6000 years) at around 240ppm. However since the Industrial Revolution this has been rising. Between 1750 and 1800 the average CO2 levels was 278ppm and it is from this baseline that the IPCC has been measuring increases. It has been suggested that between 280 and 350ppm represents a safe level. However we have past 350ppm in 1987. In 2018 scientific models suggested carbon dioxide levels of 425-785 ppm would lead to 1.5 °C temperature rise, and and 489-1106 ppm for 2 °C.

As of January 2024 the level of carbon dioxide had risen to 423ppm. In 2023 global temperatures were 1.5 °C higher than the pre-industrial average – but this in part was due to the El Niño effect, so in terms of human-made heating, the rise for 2023 is calculated at 1.3°C of warming. 

The red lines and symbols represent the monthly mean values, centered on the middle of each month. The black lines and symbols represent the same, after correction for the average seasonal cycle. The latter is determined as a moving average of SEVEN adjacent seasonal cycles centered on the month to be corrected, except for the first and last THREE and one-half years of the record, where the seasonal cycle has been averaged over the first and last SEVEN years, respectively.