Sea-level rise

פורסם: 9 ביולי 2013, 11:50 על ידי: Sustainability Org   [ עודכן 9 ביולי 2013, 11:50 ]

Since the early 1990s, scientists have used satellites to measure global sea-level rise with great precision – on average it has been around 3 mm every year.  However, there is evidence that this rate has risen in recent decades and by the end of this century a total sea-level rise of around 1 metre is possible (compared to levels recorded in 1990).

Currently, sea-level rise is the result of several different climate-driven processes: thermal expansion of the oceans (~1 mm per year), melting of mountain glaciers around the world (~1 mm per year), and retreat of the world’s polar ice-sheets* (0.7 mm per year). Thermal expansion and melting mountain glaciers can be predicted with confidence; the greatest remaining uncertainty lies in the contribution of ice-loss from the polar ice-sheets resting on Antarctica and Greenland.

European sea-level rise

Fifteen EU countries have substantial coastlines that will be affected by global sea-level rise. Within these coastal regions

  • economic assets within 500 metres of the sea have an estimated value between €500 and €1,000 billion;
  • 47,500 km2 of sites within 500m of the coastline are identified as having high ecological value;
  • the population has more than doubled to 70 million people – currently 14% of the entire EU population.

In many of these coastal areas, future sea-level rise will increase rates of coastal erosion, accelerate the destruction of natural sea defences, and increase the risk of coastal flooding. Developing policies to protect our coastlines, and reduce the impact on lives and livelihoods of EU citizens demand the best projections of sea-level rise available.

Ice2sea is specifically focussed on the contribution to sea-level rise that will arise from loss of continental glaciers and ice sheets and which give rise to the largest part of the uncertainty in the projections. Sea levels will also rise due to thermal expansion of the oceans – however studying this is beyond the scope of this project – ice2sea only studies contributions from glaciers and ice sheets.

Global sea-level rise

This collaboration of scientists draws together the EU’s scientific and operational expertise in order to better understand sea-level rise and the uncertainty surrounding it. Using past records, observational measurements and computer modelling techniques, ice2sea scientists are:

  • Measuring current rate changes in glaciers and the polar ice-sheets
  • Understanding the processes by which glaciers and ice-sheets are affected by atmospheric and ocean change
  • Developing new projections of sea-level rise for European coasts over the next 100-200 years.

In Greenland, ice2sea scientists have drilled to the bottom of the ice-sheet, to measure how meltwater produced on warm summer days, finds it way to the bed of the ice-sheet where it lubricates the bed, and allows ice to flow faster.  These data are crucial in predicting the behaviour of the ice-sheet in a warming climate when summer melting will increase.

Results from this and other field campaigns are delivered to different groups within ice2sea.  In particular, to the computer modelling teams who are building a new generation of more complete and precise methods of projecting the contribution of ice to sea-level rise. This work begins with projections of global climate based on different emissions of greenhouse gases.  These global climate models are then used to drive regional atmospheric models that allow projections of the direct specific atmospheric changes likely to occur in Greenland and Antarctica, and ocean models that predict how oceans deliver heat to the ice sheets.  Several new ice sheet models are beginning to be developed, and these will be driven using the atmosphere and ocean model output, to predict the changes in the ice sheets.

In another part of ice2sea, we have built a new inventory of the world’s 100,000 mountain glaciers.  We will use our global climate projections, and a statistical model of glacier change to make similar projections for glaciers.

Finally, the projections of ice-loss from the ice sheets and glaciers around the world will be fed into one more model.  This model, will tell us how the melting ice will be distributed around the World’s oceans and seas, and thus how global sea-level change will be felt on specific coastlines, in particular in Europe.

 *Ice-sheets are thick layers of ice formed from snow, which is then compacted on land. As ice-sheets flow towards the coast they eventually break away as icebergs and melt in to the sea.