Seasonal variations in carbon dioxide level vary in amplitude (size) and in phase (timing) between different parts of the World.
In regions with low levels of vegetation (such as deserts and snow covered areas) there is a low amplitude variation, possible as small as 2 ppmv. In well-vegetated regions the annual variation may have an amplitude as high as 16 ppmv.
The size of the annual variation depends on the amount of vegetation in a wide area surrounding the sampling point since carbon dioxide can diffuse significant distances (thousands of kilometres) on a time scale of months.
The phase (timing) of the cycle varies between the northern and southern hemispheres with maxima in CO2 levels occurring in about April (the end of Winter) in the northern hemisphere and in about October (the end of Winter) in the southern hemisphere.