Stochastic secular trends in sea level rise

Abstract

Global mean sea level (GMSL) has been rising since (at least) the 19th century and the rate of rise may be increasing. Several studies that attempt to explain the long term trend of GMSL during the instrumental record share the common assumption that this trend is deterministic in nature and different from natural variations. Here we show that the trend can alternatively be explained, at least in part, as being caused by random variations within the coupled ocean-atmosphere-cryosphere system, and hence not having a deterministic origin. These random trends, which add to externally forced changes (e.g. through anthropogenic climate change), are a consequence of the integrated character of GMSL, which is the cumulative addition of temporal contributions that exhibit random character, and whose integration results in GMSL variations with persistence on decadal-centennial time scales. The generation of trends by integration of random stationary noise (i.e. even in a constant climate) is a robust and fundamental feature of stochastically forced systems with memory. The integrated character of GMSL results in an intrinsic difficulty in distinguishing internal from externally forced trends. This article is protected by copyright.