If we now get a period of natural cooling it might well last several decades.There has been a gradual background and wholly natural warming trend since the end of the Little Ice Age. (newclimatemodel.com)
Worldwide there was a significant natural warming trend in the 1980's and 1990's as a Solar cycle peaked with lots of sunspots and solar flares. (dotearth.blogs.nytimes.com)
I think that it would be impossible to argue that there couldn't be shorter timescale natural warming trends based upon evidence presented in both these studies. (realclimate.org)