Natural variability in the climate system, occurring on a decadal timescale, is a large contributor to global temperature trends, although its influence has decreased relative to increases in warming resulting from human activities reports an article published online this week in Nature Climate Change.

Masahiro Watanabe and colleagues used two types of climate model to determine the contribution of natural decadal variability to observed global surface air temperature changes. The first was a coupled ocean-atmosphere general circulation model with observed wind stresses to simulate historical temperature changes from 1961 to 2012, and the second model was an atmospheric general circulation model.

The authors find decadal variability accounted for about 47% of temperature change in the 1980s (relative to the 1961-1990 reference period), while for the 2000s it dropped to about 27%. This change is due to the increase in external influences, such as human-caused greenhouse gas emissions, solar activity and volcanic eruptions.