hunter,
Besides the increase in tropospheric temperatures over the past 40+ years, the biggest one is the accumulation of heat in the oceans. Approximately 23 x 10^22 Joules down to 2000 meters has been stored, and hints of even more at yet deeper levels. This is far more than the atmosphere of course, and the atmosphere is far more subject to shorter term fluctuations such as from ENSO, volcanoes, solar (i.e. it is a noisier signal).