Ecosystems provide many products and services that are crucial to human survival (Daily, 1997; UNEP, 1998; WRI, 2000). Ecosystems affect biogeochemical and physical feedbacks to the biosphere and atmosphere, hence are important for the functioning of the Earth's systems. Ecosystems form a landscape and are connected in many ways, often by streams, rivers, and wildlife. Thus, landscape fragmentation, along with other human activities, affects ecosystems' ability to meet human needs and will continue to do so for the future, possibly at a faster rate (UNEP, 1998). Changes in global climate and atmospheric composition are likely to have an impact on most of these goods and services, with significant impacts on socioeconomic systems (Winnett, 1998).

This chapter assesses the impacts of climate change on ecosystem goods and services from sectors such as agriculture, forests, and wetlands. Inland aquatic systems are covered from an ecosystem perspective in this chapter; hydrology and water as a physical resource are covered in Chapter 4. Marine and coastal systems are considered in Chapter 6. When ecosystems are highly managed, as in agriculture and forestry, or their goods and services are traded in markets, the social and economic consequences of climate change that naturally arise are assessed explicitly.

Biomass production, biogeochemical cycling, soil and water relationships, and animal-plant interactions (including biodiversity) are considered to be some of the major functions of ecosystems. Within these functions, various products (goods) and services can be identified, including food, fiber, fuel and energy, fodder, medicines, clean water, clean air, flood/ storm control, pollination, seed dispersal, pest and disease control, soil regeneration, biodiversity, and recreation/amenity (UNEP, 1998; WRI, 2000). Society places values on these goods and services, directly or indirectly (Table 5-1). Ecosystems provide many of these goods and services simultaneously. For example, agricultural systems provide much of our food, fiber, and fuel needs and at the same time influence biogeochemical cycling, soil and water quality, and biodiversity. Many services from ecosystems lie outside market systems, making it difficult to price them (Bawa and Gadgil, 1997; Goulder and Kennedy, 1997; National Research Council, 1999). However, these nonmarket values are likely to be larger (as much as 1,000-fold; WRI, 2000) than the value of services provided by markets in total and at many specific sites (Costanza et al., 1997). Although several studies estimating different values for nonmarket services from ecosystems exist (see Table 5-2), they can be applied only with low to medium confidence (Goulder and Kennedy, 1997). Valuation of ecosystem services is complex because many goods and services occur simultaneously. Thus, it is not sufficient to consider, for example, the timber value of the forest; we also must consider the soil/water protection that the trees provide, the habitat for pollinators, or the bequest value of the forest (WRI, 2000).

The Earth is being subjected to many human-induced and natural changes, often referred to as global change. These changes include pressures from increased demand for resources driven by economic growth, increased human population, land-use and land-cover change, the accelerated rate of anthropogenic nitrogen production and other air pollutants, and urbanization and industrialization; resulting fossil fuel emissions contribute to a discernible impact on global climate (Naiman et al., 1995a; Vitousek et al., 1997a; IPCC, 1998; UNEP, 1998; Walker et al., 1999). For ecosystems, the impacts of climate change include changes in atmospheric composition and disturbance regimes, such as frequencies of fires, storms, floods, and drought. The impacts of other pressures often lead to increased demand for access to land, water, and wildlife resources. The result is a change in the state of the Earth's land surface, the services humans receive, and the landscapes where humans live at regional and global scales. Governance and equity issues are important (UNEP, 1998) in overcoming some of these; these are covered in detail in TAR WGIII Chapter 1.

Understanding the current status of ecosystems, pressures on them, and their responses is important for assessing the impact of the additional pressure of climate change. The State-Pressure-Response model of the Organisation for Economic Cooperation and Development (OECD) has been used as a framework in structuring many subsequent sections of this chapter (see Figure 5-1). Using this model, the "state" refers to assessments of current status and recent trends of each sector and "pressures" include direct and indirect human pressures. The concept of "response" has been modified to include automatic responses of ecosystems (referred to as automatic adaptation in Chapter 18) to the impacts of climate change (including that of natural climatic variability). Deliberate "adaptation" options to climate change to overcome some of these impacts-responses could alleviate some of the pressures. Systems that are not able to adapt are likely to become vulnerable (see Chapter 18); thus, vulnerability also is assessed.

In many sections, four goods and services have been emphasized because of the availability of literature and space constraints: food, fiber, carbon storage, and biodiversity. Many other topics—for example, related to water cycling and hydrology—could have been considered. Some of these are covered in other chapters of this report (e.g., Chapter 4 and as key regional concerns in Chapters 10-17).

Some impacts of global change apply across many sectors and are considered in Section 5.2. Many of the impacts of climate change are projected by using models, and Section 5.2 includes a critique of several of these models. Some studies in the literature already have identified regional impacts of post-industrial climate change on some ecosystems. These are discussed in the most appropriate sections under "impacts-response" but are dealt with mainly in Sections 5.2 and 5.4.

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