The solid blue curve shows the observed northern Hemisphere temperatures and the dashed blue curve
is a smoothed version. The red curve is the temperature history for a model that responds to the
external forcing of greenhouse gases and solar variability but not to natural climate variations.
The blue alternations about the red curve represent the natural AMO oscillations. When the AMO
decreases, as from 1950 to 1975, global warming may appear to be reversed. When the AMO increases,
as from 1975 to the present, the global warming (red) is exaggerated. (adapted from Goldenberg et
al. 2001; )