Assessing impacts and responses to global-mean sea-level rise

One of the more certain impacts of human-induced climate change is a rise in global-mean sea level (Nicholls and Lowe, 2004). While the impacts of this sea-level rise are confined to coastal areas, these include the most densely populated land areas on Earth and they support important and productive ecosystems that are sensitive to sea-level change. Further, coasts are also experiencing significant human-induced modification, so sea-level rise and climate change are an additional stress, which amplifies their impacts (Bijlsma, 1996; Kremer et al., 2005). During the twenty-first century, global-mean sea-level rise will likely be less than 1 metre (Church and Gregory, 2001), but still potentially directly affecting at least 200 million people based on 1990 population (Hoozemans et al., 1993; Mimura, 2000). Over the longer term (many centuries), a much larger sea-level rise exceeding 10 m is possible under some emission pathways owing to ablation of the Greenland Ice Sheet and collapse of the West Antarctic Ice Sheet, among other changes (Oppenheimer and Alley, 2004; Nicholls and Lowe, 2005). Further, the high human exposure to sea-level rise is increasing rapidly because of global population growth and coastward migration. Therefore, any global assessment of the climate change issue must include the coastal implications. A fundamental result that has long been recognized by climate scientists, but less considered by policy, is that irrespective of future greenhouse gas emissions, there is a “commitment to sea-level rise” (Nicholls and Lowe, 2004; 2005).