Chapter 18 - Rising Sea Levels as an Indicator of Global Change

Abstract

The release of the fourth assessment report of the Intergovernmental Panel on Climate Change (IPCC) in 2007 was followed by much debate, both in the media and in the scientific community, on the sea-level rise predictions it contained. This was partly because sea-level rise is an effect of global climate change that will have far-reaching consequences for a majority of the world's population. Collectively, the data summarized by the IPCC reflects the improved understanding of the causes of sea-level rise and they identify rising sea levels as one of the major indicators of ongoing global change. Sea level has been rising at rates of up to 0.06 m per decade in the twentieth century. Since the 1950s, every subsequent decade has experienced increased rates of sea-level rise. Model experiments show that twentieth century sea-level rise cannot be explained by natural processes alone. Anthropogenic forcing by greenhouse gasses has become a dominant cause for recent sea-level change. The geological record of the past three glacial-interglacial cycles shows a strong positive relationship between atmospheric CO2 concentrations and sea level. Modern rates of sea-level rise started about 100 years ago and the rate of twentieth century sea-level rise appears to be faster than rates reconstructed for the warm intervals of the Medieval Climatic Optimum and the middle Holocene. However, during the last Interglacial rates of sea-level rise were possibly higher and were similar to those predicted in some future climate-change scenarios.