Download There is an unknown but small probability that the West

ATLANTIS POLICY MAKERS SUMMARY
Atlantic Sea Level Rise: Adaptation to Imaginable Worst Case Climate Change
There is an unknown but small probability that the West-Antarctic Ice Sheet (WAIS) would
collapse because of anthropogenic climate change. The probability is greater than zero, as the
WAIS has disappeared in the geological past. The probability is small, as the current WAIS
has been around for a long time (nearly 100,000 years), withstanding natural climate change.
The ice sheet dynamics are complex and insufficiently understood. We therefore do not know
how the WAIS would respond to global warming.
We do know that, if the WAIS would collapse, it would raise the mean level of the sea by 5 to
6 metres. This could happen relatively fast, as the WAIS would slide into sea before melting.
The physical movement of the ice sheet determines the rate of sea level rise; the WAIS can
move much faster than it can melt.
The ATLANTIS project did not study the WAIS. Rather, it studied what would happen if the
WAIS were to collapse. The central scenario was an additional five metre sea level rise within
a century. This scenario is the worst case scenario, verging on the boundaries of what is
physically possible. The aim of such an exercise is of course not to provide a credible estimate
of the impacts. For that, one would need to look at an average scenario. An extreme scenario
as used in ATLANTIS can be used to draw a reverse conclusion: If society can cope with the
worst case, then there is little reason for concern. However, the results indicate that 5-6 metres
sea level rise in a century would cause severe problems, even in rich, technologically adept
and well-organised societies such as France, the Netherlands and the United Kingdom.
Three case studies were conducted, in the Rhone delta, the Thames estuary, and the
Rhine/Meuse delta. The case studies combined fairly straightforward impact studies with
extensive consultation of experts and stakeholders, emphasizing what is important (according
to the stakeholders) over what can be quantified.
The Rhone delta, better known as the Camargue near Arles and Marseilles, would probably be
abandoned. The major population centres would be safe, but losses of villages, infrastructure,
cultural heritage, agricultural land, and nature would be substantial, although wetlands might
expand.
London dominates the Thames estuary. Here, the more likely strategy would be a mixture of
protection and retreat. Complete protection by a new and larger “Thames Barrier” further
downstream would be complicated and expensive, and may well fall victim to paralysis in
decision-making. Instead, the historic heart of the city1 would be transformed into the Venice
of London, while lower value residential and industrial areas (e.g., Essex, North Kent) would
be given up.
The Rhine and Meuse deltas are the core area of the Netherlands, including three of the four
major cities (Amsterdam, Rotterdam, the Hague). It is technically and economically feasible
to protect the country, which is already below sea level at present. It would require a major
infrastructure project, including not only dike reinforcements, but also new rail links to
transport the material, and new power stations to pump the river water into the sea. It is
unlikely that such a project would be able to harness the necessary political will, before a
severe flood would focus the minds. After the first flood, it is questionable whether there
would be enough time to sufficiently reinforce the dikes to prevent a next flood. People and
companies would feel unsafe and migrate, reducing the need and the capacity for dike
1
The City, the financial heart of London, is situated near the river but on higher ground. Canary Wharf, the
“New City” is highly vulnerable.
reinforcements. If the sea were to rise by five metres in a century, the lower parts of the
Netherlands, roughly two-thirds of the country, would probably be given up.
The pessimistic results of the three case studies are partly contradicted by the results of a
global impact model of sea level rise. This model is driven by a cost-benefit analysis of
coastal protection, rather than a political analysis as in the case studies. The model suggests
that it would be worthwhile to defend the coastline in developed countries, which will be
richer still in the future. Protection costs would soar, but be bearable. In poorer countries, land
losses would be dramatic. The model foresees mass migration, but does not include the
impacts of that. Even though the model results are less pessimistic than are the case study
results, they do cause concern.
Formal risk assessment and cost-benefit analysis confirm the intuitive notion that the mere
risk of a WAIS collapse justifies greenhouse gas emission reduction. As ATLANTIS did not
estimate the probability of a WAIS collapse, and quantified the impact of only a few potential
scenarios, it does not yield insight into what constitutes dangerous climate change or what
would be an optimal level of emission reduction. Nonetheless, it would be advisable to reduce
the probability of the WAIS collapsing.
Besides climate policy, ATLANTIS also yielded insights into coastal zone management. The
Rhone case study highlighted the need for forward planning. The Thames case study
emphasized the importance of thinking beyond the officially sanctioned sea level rise
scenario. The Rhine case study stressed the difficulty of major infrastructure projects in
densely populated metropolitan areas.
Detailed results of the ATLANTIS project can be found at:
http://www.uni-hamburg.de/Wiss/FB/15/Sustainability/atlantis.htm
The ATLANTIS project was financially supported by CEC DG Research under contract
EVK-CT-2002-000138. The project was conducted by the Centre for Marine and Climate
Research, Hamburg University; the International Institute of Applied Systems Analysis; the
Flood Hazard Research Centre, Middlesex University; the Stockholm Environment Institute
and its Oxford Office; the Institute for Environmental Studies, Vrije Universiteit Amsterdam;
and Institut Symlog de France.