The most recent climate shift probably occurred at about the year 2000. Now the question is how has warming slowed and how much influence does human activity have? “But if we don’t understand what is natural, I don’t think we can say much about what the humans are doing. So our interest is to understand—first the natural variability of climate—and then take it from there. So we were very excited when we realized a lot of changes in the past century from warmer to cooler and then back to warmer were all natural,” Tsonis said.  Tsonis said he thinks the current trend of steady or even cooling earth temps may last a couple of decades or until the next climate shift occurs.