Sea Level Rise Predictions - Alarmist or Alarming?

Sea level rise is one of the more well-known impacts of climate change. The melting of ice at the poles and the corresponding increase in sea level is a concept readily understood by many.   As well as the transfer of water from glaciers and ice sheets into the oceans, rising temperatures also lead to the ‘thermal expansion’ of seawater.  The slow rate of the oceans’ response to rising temperatures means that sea levels are certain to continue to rise in coming years as a result of warming that has already occurred, even in the unlikely event of drastic action to curb emissions.   Accordingly, coastal communities around the globe are facing up to the challenge of rising seas.  Innovative and architecturally bold flood defences are proposed to protect New York from storms like Hurricane Sandy that inundated the Big Apple in 2012. At home, the City of Bristol is taking a strategic view on protecting the city.  Many other ‘at-risk’ areas are also populated by some of the world’s poorest adding to the potential for devastation.   Recently, former NASA scientist James Hansen co-authored a paper that suggests that “several metres” of sea level rise is possible even if we limit global temperatures to a two degree rise.  What’s staggering  is that the authors’ models see this  occurring over decades - rather than centuries - as a result of complex feedback effects between air temperatures, ocean circulation and ice loss.  The paper presents an alarming view of society failing to accommodate sea level rise of this magnitude, resulting in the loss of major parts of the European lowlands, North America and some of the world’s most densely-populated areas like Bangladesh to the sea.  The authors have taken the unusual step of publishing online, in advance of peer review, to provide a catalyst for action at the 2015 United Nations Climate Change Conference in Paris.  It’s therefore unsurprising that several leading climate scientists have already raised caution about the study and re-asserted that a sea level rise of around one metre by 2100 remains the consensus view.   What ‘outlier’ studies like Hansen’s do provide is an indication of just how much uncertainty there is in the scientific community about the influence of feedback effects that amplify the rate of sea level rise and the scale and speed of any impacts that result.   In the short-term, the potential for sea levels to rise, even up to one metre, poses a risk to those owning, occupying or investing in coastal sites.  As the science hardens and uncertainty about the rate and impact of sea level rise reduces, an understanding of vulnerability will be crucial in protecting investments and guarding against losses.  With so much of our economic development, infrastructure and energy reliant on the coast, and swathes of our most productive farmland being near to, or below, current sea levels, should Hansen’s predictions be shown to be more than alarmist politician-baiting, the results could irrevocably change our way of life within a generation.