Slide 4 of 30
Notes:
This graph shows atmospheric carbon dioxide as a function of latitude and time, over a 4 year period. In the northern hemisphere spring, land vegetation uses photosynthesis to make leaves and new wood, drawing down atmospheric CO2 in those latitudes. Throughout the year, respiration from decay of dead leaves and wood is restoring the concentration towards an annual balance. The net effect is a minimum in late summer. The southern hemisphere, on the other hand, has less land and vegetation cover, so the oscillation, though perceptible and of opposite phase to that in the north, is of much smaller amplitude, being further diminished by mixing in the atmosphere across the equator.