Observed enhanced greenhouse effect

In 2001, Harries et al published an article claiming to infer changes in greenhouse radiative forcing from changes in the Outgoing Longwave Radiation (OLR).  Here is the crucial data from that paper:

The graph shows the difference in OLR between April-June, 1970 and April-June 1997 over the eastern central tropical pacific (10 S to 10 N; 130-180 W).  It shows that the OLR has increased slightly (top), but that the observed increase was matched by an predicted increase in the models (middle).  The graphs are offset to allow easy comparison.