The all-dominant climate driver on the decadal scale is volcanism
and the large eruptions are triggered by the Moon caused by the 9 years perigee cycle. The Moon's perigee is moving forwards in its orbit, and makes a complete circuit in about 9 years.
The volcanic influence is also clearly seen in the sea-level change rate
The lunar influence is also important on the annual scale as it is causing solar eclipses with a 3.6 years periodicity. Every 3.6 years (avg) there are eclipses at low latitudes and temperature tend to increase. Perhaps mass is pulled towards the equator slowing down Earth's rotation which again could have an impact on the trade winds.
There is even a 'PDO-signal' in the eclipse curve,10 yr average.
Eclipse data from
http://eclipse.gsfc.nasa.gov/SEpubs/5MCSE.html by Fred Espenak and Jean Meeus
update 28. apr. 2010:
