3. Worldwide loss of biodiversity


Climate Change and Biodiversity Conservation



Of some things there is no doubt. The Earth's biodiversity is undergoing a highly deleterious simplification as the result of human activities. Biological diversity is generally taken to mean the combination of genetic variation, species richness, and ecosystem and landscape diversity. Biodiversity at all levels is currently being lost at an unprecedented rate. Just one measure of this loss is the rate of species extinctions. Background extinction rates through geological time have been roughly estimated at the rate of one mammal and two birds every 400 years. Documented extinctions for mammals and birds during the last 400 years are already at 50 times that rate and even this figure is undoubtedly a major underestimate. The highest levels of biodiversity are in the tropics, particularly in tropical forests. Estimates for the total number of species range between five and 30 million species, less than two million of which have been described by science. The top end of this range is based largely on estimates of insect species richness in tropical forests. Current rates of extinction from the tropical forest biome alone have been estimated at 1-11 per cent per decade.


There is a tendency for the issue of species extinctions to gain the greatest attention in any public debate about conservation and biodiversity loss. In fact, ecologists are becoming increasingly concerned with maintaining diversity at all levels. Today's conservationists are concerned with preserving and maintaining the full range of biodiversity and functional values of ecosystems, not merely popular species or more unusual habitats. The concept of ecosystem integrity is often used to describe the full set of values that we should strive to maintain in our natural areas. American conservation biologist Reed Noss has argued that preserving ecosystem integrity involves elements of ecosystem health, biodiversity, stability, sustainability, naturalness, and beauty. In other words, we should seek to conserve a broad range of interlinked values in ecosystems, the subsequent outcome of which is likely to determine the robustness, or otherwise, of natural areas to a changing climate.




Environmental hazards: habitat destruction, pollution, over­ exploitation of natural resources, climate change



Human­induced climate change adds another layer to the already complex interplay of forces, natural and anthropogenic, that shape our natural world. For too long nature has been regarded as stable or constant in its make­up. It is, in fact, highly dynamic, with most ecosystems being in some form of transient state. It has been said with good reason that "ecosystems are not only more complex than we think, but more complex than we can think".


The need to prepare for adaptation to climate change is highlighting the issue of ecological dynamism and complexity for the scientific community and the public at large. Climate change impacts will not be imposed on stable communities of plants and animals, but on ecosystems that are constantly in a state of flux. For this reason, impacts will be particularly hard to predict.


Further complicating the analysis of climate change impacts are the effects of ongoing environmental degradation. Leading causes of biodiversity loss worldwide include habitat destruction, pollution, introduction of alien species, and overexploitation of wildlife, fisheries, and forests. High amongst the driving forces behind these problems are demographic change (including population growth), consumption patterns, inefficient energy use, and commodity trade. The net result of these many stresses is a loss of diversity and a simplification of ecological complexity. These changes reduce the resilience of ecosystems and weaken their capacity to adapt to climate change. Ecological complexity is a prerequisite for ameliorating the negative impacts of global climate change.


Already there are indications of how climate change could be affecting ecosystems and species worldwide. These include:



  • A warming trend and decreasing spring rainfall during the last 100 years have increased the risk of wildfires in Yellowstone National Park.

  • The warmer, drier climate this century has also allowed an unprecedented expansion of juniper woodlands in the intermountain region of the western US. And sub­alpine firs and mountain hemlock are invading alpine flower meadows.

  • Climate change is one of the key factors that threatens a rare fritillary butterfly with extinction as the last remaining mountain­top habitats of Colorado become too warm.

  • Sediment cores from the frozen mud of high­arctic lakes on Canada's remote Ellesmere Island reveal that after nearly 8,000 years of stability in lake vegetation, the 19th and 20th centuries brought about major changes in lake flora, consistent with a warming trend.

    An increase in the death of coral reefs as a result of "bleaching" associated with warmer water temperatures has been reported recently from reefs around the world, including those in Indonesia, the Philippines, Jamaica, and Pacific island nations such as the Cook Islands and American Samoa.

  • Deforestation in the rainforests of Xishuangbanna in South China has led to local climate changes, including a reduction in the cloud and fog necessary to maintain moisture­dependent plants such as mosses, ferns, and orchids in the forest canopy.

  • A long­term drying trend in central Panama appears to be leading to major changes in forest composition and reduction in diversity. In the rich tropical forests of Barro Colorado Island, several shrub and tree species are heading for local extinction.

  • The current severe die back of coastal mangrove forest on the island of Bermuda has been strongly linked to sea­level rise.



Additional signposts to the future climate can be discerned from examining the pattern of extreme weather events. The impacts of disasters such as Hurricane Hugo's devastating run through the Caribbean in 1988, the southern African drought of 1991-1992 or 1995's catastrophic floods in northern Europe are likely to be repeated more frequently as the climate warms.




Recent extreme weather events are a foretaste of the future



Of special concern is the phenomenon known as El Niño, a periodic alteration of the winds and ocean currents in the tropical Pacific. Weakening of the normal easterly winds triggers El Niños by suppressing nutrient­rich cold­water upwellings and warming of the sea surface. The severity of El Niños varies sharply, and whilst the weaker ones are noticed mainly in South America, where marine fisheries drop off markedly, stronger ones are felt around the world. There have been nine El Niños in the last 40 years, but the strongest of the century occurred in 1982-1983.


The global economic costs of damage from floods, droughts, and hurricanes caused by this massive weather perturbation have been estimated at well over US$8 billion. During the 1982-1983 El Niño, tropical storms hit islands that seldom suffer from such events, including Hawaii and Tahiti. Huge forest fires raged in Indonesia and Australia, and winter flooding spread throughout the southern United States. Meanwhile the anchovy fishery off Peru and Ecuador crashed, and episodes of bleaching due to the warm waters killed off corals around the world. Huge portions of Pacific populations of seabirds such as cormorants, terns, and boobies starved to death, as did fur seals and sea­lions. Now, as the climate warms, many scientists believe that El Niños may become more frequent and severe, with their impacts becoming increasingly devastating. Climate change may be taking us into unknown territory and creating a world of violent and unpredictable weather.




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Copyright 1996, The World Wide Fund For Nature