Despite these cycles, there is a clear trend of increasing CO2 levels. Since the Industrial Revolution, human activities have led to the release of huge amounts of CO2 into the atmosphere. These quantities are increasing every year. Once in the atmosphere, CO2 accumulates. It can even stay there for up to 1000 years. The rate of atmospheric CO2 is therefore constantly increasing. In May 2021, it reached its highest value in 4 million years.

The Mauna Loa observatory has, in fact, measured a rate of 419 ppm. “Ppm” is the abbreviation of parts per million. This means that for one million molecules of air (not counting water vapor), there are 419 molecules of CO2. This may not sound like much, but it is already 50% higher than the pre-industrial rate. Until 1850, the CO2 level was stable around 280 ppm.

Even more than this peak, which could only be an extreme value, it is the rate of growth of the CO2 content that is worrying. The Mauna Loa Observatory averages the annual growth rate of CO2 over ten years. The growth rate is how much the CO2 level has increased between January 1 of a year and December 31. Over the decade 2010-2019, on average, CO2 is increasing by 2.4 ppm per year, the highest ever recorded.

In the history of the Earth, CO2 levels have often increased but never so rapidly. For example, during the last ice age, CO2 levels rose by 80 ppm in 6,000 years. In comparison, it took only 42 years, from 1979 to 2021, to increase CO2 levels by the same amount.