Recently the little ice age was formally resurrected:
As found earlier in the Greenland ice record:
The northern hemisphere temperature record shows also distinctive cycles:
original data was at: http://www.cru.uea.ac.uk/ftpdata/tavenh.dat
version 2: http://www.cru.uea.ac.uk/cru/data/tem2/tavenh2v.dat
If the Medieval Warm Period (MWP) and the Little Ice Age (LIA) are real, then the current warming is not human induced, but part of a 1200 year cycle.
The graph is based on the following recorded cycles MWP-LIA dans2 dans1 ENSO Max (y) 1100 1830 2003 1998 Period 1200 181 61 5 temp 0.5 0.2 0.2 0.15 Try varying the cycles yourself. Excel 2000: http://members.casema.nl/errenwijlens/co2/cycles.xls Excel 95: http://members.casema.nl/errenwijlens/co2/cycles95.xls I admit this exercise has some flaws, as the period and amplitude are held constant, in real life noise adds a frequency modulation and amplitude modulation to the data, and also the observed signal is not a pure sine wave. But overall it shows that the human effect is quite marginal, if not totally absent. Mind you, the cru data is not corrected for urban heating. ;-) The MWP-LIA cycle is referred to as "1-2 kyr climate cycle." in: The 1,800-year oceanic tidal cycle: A possible cause of rapid climate change Charles D. Keeling* and Timothy P. Whorf http://www.pnas.org/cgi/content/full/070047197 this page: http://members.casema.nl/errenwijlens/co2/cycles.htm homepage: http://members.casema.nl/errenwijlens