Climate Change 2001:
Working Group II: Impacts, Adaptation and Vulnerability
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19.3. Impacts on Unique and Threatened Systems

19.3.1. What are Unique and Threatened Systems?

Unique systems are restricted to a relatively narrow geographical range but can affect other entities beyond their range. Indeed, many unique systems have global significance. The fact that these unique entities are restricted geographically points to their sensitivity to environmental variables, including climate, and therefore attests to their potential vulnerability to climate change.

Identification of these unique entities provides the first reason for concern regarding vulnerability to climate change. In this section, we provide examples of unique entities that are likely to be threatened by future changes in climate. From those treated by WGII, we address physical, biological, and human systems. We offer a few examples in each system: tropical glaciers, coral reefs, mangrove ecosystems, biodiversity "hot spots," ecotones, and indigenous communities. These are meant only as illustrative examples; there are many unique and threatened entities. Table 19-1 lists some unique and potentially threatened systems in relation to climate change thresholds that may cause adverse effects. Table 19-2 lists some of the unique and threatened systems that are discussed elsewhere in the TAR.

19.3.2. Physical Systems

A number of physical systems are threatened by climate change. Among the most prominent are those in regions dominated by cold temperatures, such as glaciers. Many glaciers already are receding, and many are threatened by climate change. Other physical systems, such as small lakes in areas that will become drier (see Chapter 4), also are threatened by climate change. Changes in unique physical systems can have serious consequences for unique biological and human systems. Tropical Glaciers

Tropical glaciers are present on several mountains in Asia, Africa, and Latin America. These glaciers are valuable because, among other reasons, they are a major source of water for people living below them. For example, through a network of mountain streams, meltwater of the Himalayan glaciers contributes a sizeable portion of river flows to the Ganges, Brahmaputra, Indus, and other river systems in south Asia. Similarly, snow accumulates in winter in the high parts of the cordillera in Peru and melts during summer, becoming the main source of water for many rivers in Latin America. In addition, glaciers act as buffers that regulate runoff water supply from mountains to plains during dry and wet spells. Thus, tropical glaciers are instrumental in securing agricultural productivity and livelihoods and provide cultural inspiration for millions of people who live remote from their sources.

Because of the narrow range of ambient temperatures in the tropics, tropical glaciers are more sensitive to climate change than glaciers elsewhere (see Section 4.3.11). Indeed, records spanning several decades show accelerated retreat of several Himalayan and other tropical glaciers (see Section

In the transient phase of melting, increasing discharge will generate floods in the mountains and immediate vicinity, increased siltation of rivers, and larger sediment load in dams and reservoirs. Riparian mountain ecosystems will be impacted during their dry seasons—in the transient phase by a significant increment of downstream flow, as well as following the transient phase—by significant reduction of this flow. These changes will have tangible economic and cultural implications (see Section This example of a tropical unique entity provides an "early warning" for nontropical glaciers and their potential impacts.

Table 19-1: Vulnerability of wildlife to climate change (compiled from Chapter 5).
Geographic Area
Vulnerable to
Most continents, marine, polar regions
- Poleward/elevational shifts in ranges
- Already observed in many species in response to regional climate change
Most continents, marine, polar regions
- Shifts in phenology (e.g., breeding, arrival dates, flowering)
- Already observed in response to regional climate change
Sunderbans, Bangladesh
- Loss of only remaining habitat of Royal Bengal tiger
- Sea-level rise
Caribbean, South Pacific Islands - Habitat loss, direct mortality of birds
- Hurricanes
- Reproductive failure in seabirds
- Increased sea-surface temperature (ENSO)
Galapagos, Ecuador, Latin America
- Reduced survival of iguanas
- Reduced overwinter survival of palearctic migratory birds
- Extreme drought in the Sahel
Monteverde Reserve, Costa Rica
- Extirpation of some cloud forest reptiles and amphibians (already has occurred), elevational shift in some birds
- ENSO, warming, increased frequency of dry season mist
- Poleward shift of spring range of barnacles geese
- Increase in number of April and May days with temperatures above 6°C
- Susceptibility of quokka to salmonella
- Environmental conditions
United Kingdom
- Earlier hatching of spittlebugs
- Winter-warmed (3°C) grassland plots
- Faster growth in juvenile red deer, leading to increased body size - Warmer springs
Isle Royale National Park, United States
- Increased wolf pack size, increased moose mortality, greater growth of understory balsam fir - Reduction in winter snow cover
Western Antarctic Peninsula
- Reductions in Adelie penguin populations, increases in chinstrap penguin populations
- Increased midwinter surface air temperature, reductions in pack ice, increased snowfall
Northern Hemisphere
- Increased winter survival of some boreal insect pests
- Increased nighttime winter temperatures
Great Plains, USA, and Canada
- Reductions in waterfowl breeding populations as a result of wetland loss - Increased drought
Africa and Australia
- Wetland loss
- Increased drought
Africa and Australia Canada
- Reduced populations of some mammals
- Loss of 60% of available habitat (habitat migration blocked by Arctic Ocean)
- Increased drought
- Climate change
USA and Canada
- Reductions in populations of caribou
- Increased temperatures, snowfall, shifts in precipitation timing
- Loss of wintering habitat for eastern population of monarch butterfly
- Climate change leading to habitat change
- Loss of migratory shorebird habitat
- Sea-level rise tied to 2°C temperature increase
- Reduced habitat availability and accessibility hampering migration and survival of polar bears, muskox, caribou, and some birds - Increased temperatures, changing sea-ice regimes
United Kingdom
- Loss of habitat in 10% of designated nature reserves within 30-40 years - Climate change

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