by Horst Sterr, Wolfgang Ebenhöh and Frank Simmering

The threat to coastal zones will increase dramatically in the 21st century due to accelerated sea level rise and the increase in storm surges as a result of climate change. The research programme "Climate Change and the Coast", which we are planning and coordinating, is looking at the effects of this development on coastal waters, the biosphere, coastal dwellers and their activities on the German North Sea and Baltic Sea coasts. The aim is to understand the reaction of the natural and social system to the expected environmental changes and to develop adequate concepts for action. This project is thus taking on a pilot function in the newly established interdisciplinary climate impact research.

Hasn't the future already begun? We are tempted to ask Robert Jungk when we recall the urgent announcements and warnings from climate researchers around the world about the greenhouse effect and the hole in the ozone layer. The media are increasingly publishing reports on scientific studies that explain how the global climate system will react - or is already reacting - to the increasing release of greenhouse gases and pollutants by humans according to physical judgement. Individuals and the public are therefore already largely sensitised to this issue, and politicians are also sufficiently alarmed, at least at first glance. At least that is what one might assume from the conferences held at the highest political level in recent years. In Rio de Janeiro in 1992, a Framework Convention on Climate Change was adopted at the UN Conference on Environment and Development. This UN Framework Convention on Climate Change has been binding under international law since March 1994. Despite this, the Berlin Conference of the Parties from 28 March to 7 April 1995 failed to reach the binding resolutions that many had called for and which, in the opinion of scientists, would have to be implemented immediately to ensure rapid and effective climate protection. If what many experts already interpret as a clear trend towards anthropogenic, i.e. man-made, climate change continues, the world's coastal zones will be particularly affected.

Climate refers to the long-term combination of temperature, wind and precipitation conditions, i.e. weather events, at one location. However, a large number of physical, chemical and biological processes on land and in the oceans, such as weathering, photosynthesis or heat transport by ocean currents, also play a decisive role in shaping atmospheric conditions. Due to the vast number of possible interactions and feedbacks in the soil-water-air system, an exact understanding of the climate is extremely difficult. It takes the world's most powerful computers several months to simulate the effects that can be caused by changes in one of the forcing parameters (such as the mixing of the upper layers of water in the oceans) in a computer model over 50 to 100 years. The statements of climate experts regarding future climate changes are therefore still cautious, partly because the climate system harbours so many possible reactions, but above all because there is great uncertainty as to what measures will or will not be taken in the foreseeable future to protect the global climate. Particularly because of the uncertainties caused by mankind, i.e. by politics itself, the climatologists working on this problem worldwide want their statements to be understood more as scenarios than as reliable forecasts.

The Intergovernmental Panel on Climate Change (IPCC), established by the UN in 1988, has documented in several reports the scientific findings on how the climate will change by the year 2100, depending on the development of greenhouse gas emissions. The draft of the second overall report, which is to be submitted to the UN by the end of 1995, paints the following picture: according to the "business-as-usual scenario", i.e. unabated increase in the trace gases carbon dioxide, methane, nitrous oxide, ozone, halocarbons and others over the next few decades, the average temperature of the earth will rise by around 2.5° - 3° C on average. The speed of this warming, which will be more pronounced in the higher latitudes than in the tropics, far exceeds all natural climate fluctuations of the last 10,000 years (Holocene). Its extent is almost of the same order of magnitude as the climate change at the end of the last ice age, which was around 4°C. The increase in temperature would also be associated with higher or more intense precipitation and an increase in the frequency and intensity of storms. In the coastal regions, an average sea level rise of at least 50 cm/year (previously 20 cm/year) and an increase in extreme water levels during storm surges must be expected as a result of these climate trends.

Because the coastal zones - from a global perspective - are the most densely populated and most intensively utilised areas in the world (cities, shipping, fishing, aquaculture, tourism, industry, etc.) and are home to the most productive ecosystems alongside the tropical forests, the coasts are therefore also threatened with the greatest risks in the 21st century as a result of the climate change outlined above. This also applies if less severe scenarios, as comparatively calculated by the IPCC, are taken as a basis.

With the realisation that mankind (has) profoundly changed the global climate and thus its entire environment, the need to take a closer look at the effects of climate change has also grown. At the beginning of the 1990s, a new field of research emerged at the instigation of the IPCC: climate impact research.

In Germany, the first step was a joint initiative by the five coastal states and the Federal Ministry of Education and Research in 1991 to set up a research programme entitled "Climate Change and the Coast" under the scientific leadership of the Institute of Chemistry and Biology of the Marine Environment (ICBM) at the University of Oldenburg. The Potsdam Institute for Climate Impact Research (PIK) was then founded in 1992, with Prof Dr Hans-Joachim Schellnhuber (then Director of the ICBM) taking over as Director in 1993.

As the German Council of Science and Humanities emphasised in a statement, the German coastal region is particularly suitable as a focus for regional climate impact research. The North Sea and Baltic Sea coasts are not only particularly sensitive to climate-related effects, but their system structure has also already been severely altered by other interventions, e.g. nutrient and pollutant inputs, groundwater utilisation, artificial deepening of river estuaries, etc. A foreseeable threat to the coastal habitat therefore not only refers to its vulnerability to storm surges or other climate-related natural disasters, but also includes a foreseeable intensification of existing conflicts of use (e.g. between agriculture, nature conservation, coastal protection and tourism) as well as the probability of far-reaching changes in the marine and littoral ecosystems.

In March 1994, ZDF broadcast a vision of the consequences of climate change as we could experience them in Germany in 35 years' time under the title "Crash 2030". For the coastal region, the film drew scenarios of the demise of some North Sea islands and large parts of the undammed lowland areas of Mecklenburg-Western Pomerania. Although the currently accepted ideas of scientists do not go quite that far, they cannot consider the simulations of extensive coastal flooding shown in the film to be completely absurd either - at least not in areas where no adequate protective measures have been taken to date.

Based on the assessments presented by the IPCC, which, however, do not yet allow a regional concretisation of the climate characteristics for northern Germany, the following assumptions are currently considered plausible. While work continues on the so-called climate regionalisation, they are also used as preliminary scenarios in the "Climate Change and the Coast" research programme:

• air and water temperatures increase by 2°- 3° C.
• Warming is more pronounced in the winter months than in summer.
• Sea level rise in the North Sea and southern Baltic Sea is above average due to the shallowness of the sea basins and will be at least 50-60 cm by 2100, i.e. a tripling of the previous value.
• Stormy weather conditions will increase significantly in strength and frequency.
• The previous extreme water levels during storm surges (= design water levels for dykes) will be reached or exceeded more and more frequently.
• Increased swell leads to accelerated sediment redistribution and erosion in the shore area.
• Changes in precipitation conditions and water exchange between the North Sea and Baltic Sea mean that the salinity (salt content) of coastal waters is subject to greater fluctuations than before.

Although supported by the model calculations of climatologists, these assumed developments cannot be proven for the time being. However, as climate impact research endeavours to record and, where possible, increase the flexibility of the natural and social system in the face of external driving forces, alternative scenarios are also included in the analysis. One such scenario would be a drastic decrease in temperatures in the German coastal region, triggered by a redirection of the Gulf Stream into the western North Atlantic - a situation that is certainly being considered by renowned oceanographers.

The research programme "Climate Change and the Coast" is essentially concerned with the question of what effects organisms, ecosystems and coastal inhabitants can expect if some or all of the scenarios considered plausible become reality and what adaptation options are conceivable. There are many interdependencies and interactions between the subsystems of the coastal zone, which make it necessary, but also very difficult, to consider the entire system. The complexity of the impact mechanisms triggered by climate change can be illustrated using a few examples.

Take the Wadden Sea, for example: over the course of its approximately 5,000-year history, the tidal flats have gradually grown vertically and horizontally through the successive deposition of marine sediments. In the future, accelerated sea level rise, more energetic swells and more frequent storm surges will lead to increased erosion of the tidal flats, i.e. to a reduction and degradation of the tidal flats. As these are constricted landwards by the mainland dykes, a natural "escape" to the marsh is no longer possible. The increasing erosion and flooding pressure from the sea leads to a progressive loss of salt marshes and dyke forelands and thus to the disappearance of the special habitats of many characteristic animal and plant species. Similarly, the reduction in the size of the mudflats impairs the biological carrying capacity of this most important coastal ecosystem, e.g. as a nursery area for fish and mussels or as a resting area for migrating coastal birds. The loss of mudflats and salt marshes is all the more serious when one considers their mechanical function as "breakwaters" during storm surges or their biochemical cleansing function (absorption of nutrients and pollutants).

Example of coastal protection: The current target heights of coastal protection facilities on the North Sea coast are based on the water levels of the storm surge of 1962, which was between 4 and 6 metres above sea level. However, the supposed long-term protection is no longer guaranteed 30 years later, as the extreme water levels and dyke damage since 1975 have shown: the hurricane floods of 1976, 1981, 1990 and 1992 have already set new highs in various sections of the German Bight, and this trend is set to continue. The estuaries of the Ems, Weser and Elbe and their dykes and harbours are particularly at risk from the increasing frequency of extreme water levels, because the artificial deepening of the shipping channels has drastically increased the tidal range (e.g. from 0.2 to 4.1 m in Bremen). In order to achieve a so-called 100-year dyke safety in a sea level rise scenario of 50 cm (a figure calculated from the tidal water level plus wind and wave run-up effect during a storm surge), around DM 1 billion must be spent on coastal protection measures in both Lower Saxony and Schleswig-Holstein. For the city of Hamburg, comprehensive and efficient protection against future storm surges could probably only be achieved with the construction of an Elbe barrage (estimated cost DM 1.5 - 2 billion). For the protection of the west coast of the island of Sylt against accelerated erosion alone, approx. DM 180 million has been spent on sand pre-washing since 1972, whereby a marked increase in the necessary expenditure over the last eight years (approx. DM 20 million/year) is evident. A further strong increase in this trend is to be expected in the light of the above-mentioned scenarios. Along the Baltic Sea coast, only selective diking of low-lying areas was carried out after the flood of the century in 1872. A storm flood of the same magnitude would therefore flood large areas of this coastal landscape, including many coastal towns.

Example of economic risks: The dangers of dyke breaches and flooding on the North Sea and Baltic Sea and the associated material risks and losses are obvious as a result of climate change in the coming decades. However, other serious economic risks can also be derived from the scenarios. For example, increasing storm activity could increasingly affect commercial and recreational shipping as well as ferry traffic in coastal waters. Examples of this are the destruction of numerous sailing yachts in the Bay of Kiel by gale-force winds in August 1989 or the sinking of a Polish ferry off Rügen in February 1993. The accelerated proliferation of algae or the immigration of foreign (poisonous) species as a result of rising water temperatures could lead to considerable losses in fishing and tourism. And for the insurance industry, these negative forecasts have already become reality to a considerable extent: a worst-case scenario from Provinzialversicherung Kiel estimates the expected insurance loss for an extreme winter storm at more than DM 1 billion for Schleswig-Holstein alone. The total economic damage is estimated to be double this amount. Due to the immense losses suffered in recent years as a result of an accumulation of climate-related claims (hurricanes, floods, forest fires, etc.), this economic sector is now campaigning worldwide in favour of climate protection.

In a pilot project at the University of Oldenburg, the risk and economic damage potential on the North Sea and Baltic Sea coasts due to an (assumed) sea level rise of 1 metre is currently being recorded, as has already been done for around 30 other coastal areas at the instigation of the IPCC. Assuming the current state of coastal protection in this scenario, the estimated material damage to buildings, leisure and harbour facilities, agricultural land, etc. amounts to DM 20-50 billion (the total value of the maximum material assets affected is DM 800 billion). Despite this impressive sum, Germany is one of the coastal nations in the world that is relatively less affected if the calculated amount of damage is measured as a percentage of gross domestic product (< 0.05%). For countries such as Bangladesh, Egypt or the Marshall Islands, the losses are estimated at 10-50% of GDP.

The three example areas mentioned make it clear that the "Climate change and the coast" research programme has to deal with a very broad spectrum of coast-specific "climate impacts" and future developments in the natural and social system. It is not just a matter of analysing and describing the possible negative consequences, especially as it is not yet clear whether the positive effects of climate change might not outweigh the negative in some areas, such as coastal tourism. Another important task is to assess the social perception processes relating to the climate complex, for example: How is the issue of climate change portrayed in the media and what position do individual interest groups or economic sectors take on the issue? The ultimate aim of the programme's research efforts is to provide decision-makers in politics, public authorities and industry with a scientific basis for adequate action and response strategies in the coastal zone (= coastal zone management).

The complex issues involved in the federal-state project "Climate Change and the Coast", which is scheduled to run for at least ten years, require a high degree of interdisciplinary co-operation between climatologists, geoscientists, biologists, engineers, sociologists, economists and others, i.e. the integration of the research process from the individual sub-areas into an overarching synthesis of the results is of paramount importance. For this reason, a panel of experts has developed an integrative research concept based primarily on new methodological approaches: the modelling of hydrographic, morphological and biological processes; the linking of natural and social science models, the overall systemic and planning-oriented analysis of selected sample areas (e.g. case studies of the Weser estuary and the island of Sylt) and the recording, presentation and evaluation of resulting threats and conflicts using a geographical information system. A first attempt to test this concept and method approach "in the real laboratory", so to speak, was the joint project "Northern Summer 1992", which was carried out jointly by the Potsdam Institute for Climate Impact Research and the University of Oldenburg. With the participation of nine other research institutions, the economic, ecological and social consequences of the extremely warm and dry weather conditions over northern Germany in the summer of 1992 were comprehensively analysed. The study provides the first important insights into how the natural environment and people (would) react to individual phenomena of possible climate change. Many more of this kind must follow.

The three authors, geoscientist Priv.-Doz. Horst Sterr, the mathematician Prof. Dr. Wolfgang Ebenhöh and the geographer Frank Simmering, coordinate and supervise the research programme "Climate Change and the Coast", which was jointly initiated by the Federal Ministry of Education and Research and the North German coastal states. Sterr took over the management of the scientific Office of the large-scale project after his habilitation at Kiel University in 1991. The secretariat is based at the Institute of Chemistry and Biology of the Marine Environment (ICBM) at the University of Oldenburg. - Ebenhöh, a university lecturer in the Department of Mathematics and at the ICBM, is the overall coordinator of "Climate Change and the Coast". He was appointed to the University of Oldenburg in 1975 after his habilitation in Heidelberg and focuses on "Modelling of aquatic ecosystems" and "Theoretical ecology". - After completing his studies, Simmering initially worked as head of the "Geographical Information Systems" department at the Institute for Planning Data GmbH in Offenbach. At the ICBM, he is to set up an information system for the German coastal region.