Global environmental change issues in the Western Indian Ocean region

Abstract Mounting evidence from both instrumental and proxy records shows global climate continues to change. Analysis of near-surface temperatures over land and oceans during the past 130 years shows marked warming during the first half of this century with relatively steady temperatures through the mid-1970s followed by a rapid warming during the 1980s. The source of this warming is unclear at present. The warmest decade in the recent record is the 1980s with some of the most pronounced warming occurring in the lower latitudes, including the Western Indian Ocean. In the context of this study, the important consequences of climate warming are: (1) the potential impacts associated with rising sea level due to thermal expansion of the oceans; (2) melting of land-based ice sheets and glaciers; (3) the increased frequency, intensity, and seasonality of tropical storms and the monsoon season; and (4) changes in local land-use practices. Rising sea level, coupled with meteorological changes, creates a potential for increased coastal erosion and loss of coastal habitats such as wetlands, mangroves, and coral reef communities. These potential impacts may affect future land-use and development practices. For example, the curtailment of tourism could alter economic growth and development. Forecasting the potential regional and local impacts of global warming is not a trivial problem. General circulation models presently do not provide the necessary finescale resolution required for ascertaining such smaller-scale effects. In addition, there is little agreement between the forecasts from different models of past, present, or future patterns on such fundamental climate variables as precipitation and air temperature. The absence of quality regional and local tide-gauge data of the appropriate duration necessary for calculating changes in the relative sea level exacerbates the existing theoretical uncertainty. Nevertheless, the potential impacts do represent present-day problems resulting from the alteration and acceleration of naturally occurring processes through man's activities. These types of future problems which typify the impacts forecast as a result of global warming are occurring now, partly because of human activities. Such insular impacts in the Western Indian Ocean region should be used by local governments as case studies for educating the populace, developing remedial activities, analyzing socioeconomic patterns, and formulating long-term management and policy strategies that will minimize unwanted future changes. Finally, a regional strategy is needed to address the following issues: (1) the acquisition and interpretation of tide-gauge and other geodetic data to provide estimates of the local and regional relative sea-level rise ; (2) a plan to identify and suggest possible mitigation for regional and local activities (land use, economic development practices, industrial development etc.) that may directly contribute to enhanced global warming through the release of carbon dioxide and other radiatively active gases; (3) the development of regional and local policies (e.g. land use, coastal zoning, building setbacks, etc.) to minimize the impacts resulting from extant and possible future relative sea-level rise and meteorological changes; and (4) the linkages between potential changes in global (regional) climate and present anthropogenic stress upon the environment—that is, cumulative impact assessment. The challenge is to recognize the need for regional and local action in the absence of site-specific data, or scientific certainty.