The planet ‘breathes’

The Keeling Curve does not rise smoothly but zigzags up and down each year (while still rising overall). It looks a little like the blade of a saw. The reason is that most of the world’s seasonal vegetation is in the Northern Hemisphere. During the Northern spring and summer, plants grow, absorbing CO2. During the Northern winter, leaves fall and plants die and decay, releasing CO2. The fact that the Keeling curve sees this and zigs up in winter and down in summer proves how exquisitely sensitive the measurements are—and, because Hawaii has no seasonal vegetation, how well the instruments measure global rather than local conditions.[[University of California, San Diego. “Keeling Curve, 2002.”]]