Introduction

Coastal degradation has been widely reported around the world's coasts over the past century, and especially in recent decades as discussed later in this chapter [1,2]. This degradation can be attributed to the intensification of a wide range of drivers of coastal change that are linked directly and indirectly to an expanding global population and economy. The twentieth century was also characterised by recognition of human-induced climate change and sea-level rise, which constitutes an additional set of coastal drivers [3]. This chapter explores the relative contribution of climate change to observed coastal changes, focusing particularly on the extent to which climate change can be attributed as a significant driver of the change.

Climate Change: Observed Impacts on Planet Earth

Copyright © 2009, Published by Elsevier B.V.

CLIMATE CHANGE DRIVERS Storms Waves Sea level Temperature CO2 concentration Run-off

„»'Sub-system Sub-system i Í A sz

External Oceanic Influences

External Terrestrial Influences

Coastal System

FIGURE 1 The coastal system showing how it is impacted by climate change. The natural envi ronment and coastal inhabitants interact directly, and are affected by external terrestrial and marine issues. Climate change, including sea level rise, can directly or indirectly effect the coastal system (as can non climate drivers of change). (Adapted from Ref. [3]).

An analytical framework is adopted, based on a systems view of coasts as defined in Fig. 1. Comprising the narrow interface between land and sea, coastal systems are influenced by both marine and land surface processes. Coastal systems include intertidal zones and adjacent coastal lowlands and bays, lagoons, estuaries and nearshore waters. The connectivity of coasts with both marine and terrestrial systems is responsible, in part, for the high variability and complexity among coastal system types. In contrast to terrestrial systems that have physical gradients that can stretch over tens or thousands of kilometres, coastal biotic and abiotic gradients are often relatively short, particularly along steep rocky shores. Many coastal areas support large and growing populations and high economic activity [4,5], which are changing coastal environments. River catchments feeding to the coast are increasingly modified, such that coastal systems are also influenced by these external changes [6]. Hence, few of the world's coastlines are now beyond the influence of human pressures [7], with many being dominated by human activities

[8] and most coastal systems include elements of human development that interact with environmental changes associated with a warming climate.

Global warming through the twentieth century has caused a series of changes with important implications for coastal areas (Fig. 1). These include rising temperatures (both air and sea surface temperatures), rising sea level, increasing CO2 concentrations with an associated reduction in seawater pH, and more intense precipitation on average (with substantial regional variation). It has also been argued that tropical storms have become more intense

[9]. The tragic impacts of Hurricane Katrina on the Gulf of Mexico coast of the United States in 2005 and of Cyclone Nargis on Myanmar in 2008

emphasise the enormous devastation that these events cause, but it cannot be shown that these individual events were more intense as a result of climate change, and no firm conclusions on intensification of storms can be drawn at present.

Sea-level rise is one of the most widely cited outcomes of global warming. Rising global sea level due to thermal expansion and the melting of land-based ice is already being observed with a global-mean rise of 17 ± 5 cm during the twentieth century [9] and a slow accelerating trend [10]. Higher sea level will directly impact coastal areas, including some of the most densely-populated and economically active land areas on Earth.

In this chapter, we outline historical climate and sea-level change and discuss how this impacts coasts, but we also recognise that coastal systems are subject to many other drivers, most especially the impacts of human development. We further discuss the need to discriminate whether coastal degradation can be attributed to the effects of climate or to what degree they are related to non-climate drivers.

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