Every year, the planet breathes CO2 in and out. The exhale starts in late fall and continues until about early May, when the inhale begins and continues to late fall. This correlates to the growth and decay of plant matter in the northern hemisphere (where much of the landmass of the planet is located).
The graph of the result is what’s known as the Keeling Curve, named after Charles David Keeling, the chemist who was the first to measure CO2 levels in the atmosphere in the 1950’s.
Each year since humanity started burning fossil fuels, the amount of CO2 in the atmosphere has risen. Taken as an average over a year, CO2 has risen from about 280ppm in the mid 1700’s to 404ppm in 2016. It is anticipated this year the average will be about 407ppm, with a high point of around 410ppm in early May.
In a nod to Japanese artist Hokusai and his iconic painting, The Great Wave off Kanagawa, climate scientist Robbie Andrew, a senior researcher at CICERO (Center for International Climate and Environmental Research) created this plot showing the “wave” of CO2 as we approach the high point for 2017. A beautiful representation of a very scary set of numbers.
Under business as usual, at current rates of increase, CO2 will be approximately 900ppm by 2100. Note that at around 650ppm, there is a detectable drop in human cognitive function. And of course a 900ppm CO2 atmosphere will mean a 4.5C increase in the global average temperature, rendering significant parts of the Earth uninhabitable for humans.
You can follow the “wave”–the planet breathing CO2 in and out on an annual basis–at the Scripps Institute Keeling Curve web site.