Kwang-Yul Kim
Climate System Research Program
Texas A&M University
Background fluctuations of the Earth's climatic fields generally consist of natural variability as well as forced variability. Main sources of forced variability in the Earth's surface temperature records are greenhouse warming, volcanic eruptions and insolation fluctuations. These are a significant origin of decadal and centennial fluctuations. Forced variability, therefore, has been an essential cause of ambiguity in delineating true natural variability of the Earth's surface temperature field as well as in comparing model statistics with those of observational data. In this article, we review present understanding of forced natural variability. Specific emphasis is given to its implication on the acceptable sensitivity of climate models.