Climate Change and Sea Level: A Challenge to Science and Society
Changes in coastal Local Sea Level (LSL) in combination with changes in the risks associated with strom surges and wide-spread inundations of coastal areas may turn out to be a major, if not the major impact of climate change on human society. Environmental and socio-economic resources are abundant in the coastal zone, and these are potentially at risk. Planning adaptation strategies for the coastal zone is a challenge to society. Read more about the challenge to society ...
LSL, which is the distance between the sea surface and the underlying land surface, changes as a result of many local, regional and global Earth system processes affecting either the local height of the land surface or the height of the sea surface, or both. Understanding and modeling LSL changes, as well as assessing plausible future LSL changes, is a challenge to science. Read more about the challenge to science ...
Sea level, both on global, regional and local scales has always been changing and so has climate as a main forcing process for sea level changes. What is often not realized is the fact that over the last eight to ten thousand years Earth's climate was relatively stable and global sea level did not change significantly. The only other extended stable period during the last 200,000 years took place about a 120,000 years ago and lasted for about 10,000 years.
Even in the current phase of a stable global sea level, in some areas, sea level kept changing locally at higher rates, mainly due to land movement. However, the long period of relatively stable climate and small sea level changes in wide coastal areas allowed humans to settle in the coastal zone and to develop larger and permanent coastal settlements. The accessibility of the highly productive coastal zone, which provide humans with abundant environmental services certainly supported the rapid development of human civilizations that took place over the last five thousand years. In fact, the stable state of Earth may have been pivotal for the amazing transition from the age of hunters and gathers to agricultural and industrial societies.
Recently, humans have re-engineered Earth to an extent not understood or acknowledged by many. This re-engineering may push Earth into a state of much larger and more rapid climate variations or permanent changes, similar to those that took place regularly until some millenniums ago. If civilization could develop because of the conditions provided by a long period of stable climate and sea level, then a period with more rapid variation would pose a serious and existential threat to the civilization of today.
Here I make an attempt to explore some of the consequences, which the re-engineering of Earth by humans may have on the future of the planet. I do this by looking at potential consequences of an unstable sea level. Since we have very little observations to base our understanding on, we are facing large systemic uncertainties with respect to plausible futures. Planning of adaptation, mitigation and disaster reduction is challenged by the uncertain knowledge of what future might hold for us. In this situation, where control is hardly possible, the concept of resilience may offer a way to prepare for an uncertain future. Resilient thinking therefore needs to be developed and become an integral part of our planning and the development of settlements, infrastructure, and approaches. Particularly in the coastal zone, where the future may bring some rapid and disastrous sea level changes, such an approach is mandatory.
In support of societal planning and response to changes, it will also be pivotal to have a sustained observation system for the Earth system. Currently, we have no Earth model that could predict future sea level changes with any degree of reliability even on time scales of a few decades. In particular, the response of the large ice sheets, which hold the potential for large sea level changes, to global warming is not well understood and no models include possible dynamic responses that can lead to rapid changes. Recent observations indicated that dynamic melting is already taking place in glaciers, ice caps, and ice sheets. Our current observing systems is able to detect such dynamic response at an early stage and thus provides the basis for a forecasting of local sea level changes on time scales of a few years and maybe up to a decade. This type of "early warning" would at least give some lead time for response and mitigation of impacts.
An urgent issue concerns the continuation of the current observing system. In particular, many of the space-borne components of the multi-sensor and multi-platform system are due to drop out in the next two to three years, and in several cases no follow-on missions have been decided or planned.
The Greenland and Antarctic ice sheets are melting faster than expected: Several independent studies of the mass balance of the two large ice sheets have discovered that these ice masses display since about 2000 a rapidly increasing ice mass loss. If this trend continues, a dramatic sea level rise could occur within a few decades, requiring costly adaptation and increasing the risk of major floods with extreme disasters significantly. The new results show that a rapid response of the ice sheets to global warming and a severe rise in sea level over a few decades can no longer be ruled out as impossible. A sea level forecasting service is urgently needed in order to inform society in a timely manner if a unlikely but potentially large sea level change takes place. City managers indicated that a lead time of about ten years would be sufficient to adopt cities in low-laying coastal areas to a projected dramatic sea level rise.
Past sea level conference(s): Sea Level Rise Conference 2010, March 1-3, 2010, Corpus Christi, Texas