Chapter 1 Status and Trends of Global Biodiversity


The strong scientific linkages between global environmental issues - such as loss of biological diversity, climate change, stratospheric ozone depletion, water degradation, or the accumulation of persistent organic pollutants - are becoming increasingly apparent.

The issue may pose one of the greatest threats to biodiversity is climate change. For this reason, one of the most critical tasks is to identify the scientific and policy interlinkages between biodiversity loss and climate change. This section will look at those links.

Climate change

The weight of scientific evidence suggests that the observed changes in climate are caused, at least in part, by human activities, primarily the burning of fossil fuels and changes in land cover. These activities are modifying the concentration of CO2 and other greenhouse gases which absorb heat radiating from the earth as well as the properties of the surface which absorbs or scatters radiant energy (the albedo effect).

Climate Change

Climate change means a change of climate which is attributed directly or indirectly to human activity that alters the composition of the global atmosphere and which is addition to natural climate variability observed over comparable time periods.

Adverse effects of climate change means changes in the physical environment or biota resulting from climate change which have significant deleterious effects on the composition, resilience or productivity of natural and managed ecosystems or on the operation of socio-economic systems or on human health and welfare. United Nations Framework Convention on Climate Change, Article 1

Climate change may directly affect species through changes in phenology (e.g., earlier flowering of trees and egg-laying in birds), lengthening of the growing season, and changes in distribution (e.g. pole-ward and altitudinal shifts in insect ranges). In many cases the observed changes are consistent with well-known biological responses to climate. Changes in such characteristics of organisms may thus serve as indicators or early warnings of climate change.

Climate change is an additional stress on ecosystems and species that are, often, already under stress from other pressures such as: habitat change resulting from land-use change; over-harvesting; pollution; and the effects of invasive species. Such pressures thus make biodiversity more vulnerable to climate change. For example:
  • Habitat fragmentation poses barriers to dispersal, thereby reducing the possibility that species can adapt by moving as the climate changes. (Such barriers to dispersal may also exist naturally, in areas such as small islands or mountain tops);
  • Habitat fragmentation and over-harvesting may result in small isolated populations with low genetic diversity. With low genetic adaptability such populations will be more vulnerable to extinction;
  • Ecosystem degradation, which may result from unsustainable use of ecosystem components, pollution, pest outbreaks, or changes in fire regimes, can decrease the resilience of ecosystems to climate change.

Addressing such exacerbating factors may be an important component of adaptation to climate change.

The expected result of these interactions is that climate change will lead to reduced biological diversity. At the species level, those that are most likely to be adversely affected are those that can only tolerate a narrow range of climatic conditions and that have limited capacity to disperse. This is likely to include a significant proportion of already threatened species.

At the ecosystem level, established natural communities may be broken up as the constituent species shift at different rates in response to climate change. For example, a substantial fraction of the world's forested area is expected to undergo major changes in broad vegetation types with the greatest changes at high latitudes. New assemblages of species and hence new ecosystems may be established. As noted below, this may have major implications for the role of forests as carbon stores.

Differential responses to climate change by species in ecosystems may lead to disruption of important functional interactions, with potentially highly serious consequences for the provision of ecosystem services such as pest control, pollination, seed dispersal, decomposition and soil nutrient cycling. In addition to the effects on natural ecosystems, these could have socio-economic consequences for agriculture.

The impact of climate change on biological diversity is expected to be non-linear. The impact may be particularly severe when certain critical thresholds are crossed. Ecosystem types that are vulnerable to such thresholds include:
  • Wetlands overlying permafrost. These are likely to be severely affected when the ice melts;
  • Coral reefs. As already noted by the Conference of the Parties, there is significant evidence that climate change is a primary cause of the recent and severe extensive coral bleaching. Bleaching is reversible when the increases are short-term and of no more than 1-2ºC. However, sustained increases in water temperatures of 3-4ºC above normal maxima can cause significant coral mortality. Severe bleaching events were triggered, for example, by the El Niño events of 1982/83 and 1997/98.

Climate change may also increase threats from invasive alien species:
  • Climate change may result in extension or changes in the ranges suitable to certain invasive species. An example may be the increased prevalence of vector-borne infectious diseases transmitted by blood-feeding mosquitoes and ticks;
  • Environments may become more favourable to weedy species because of climate change induced ecosystem disruptions.
In short, and as the Intergovernmental Panel on Climate Change (IPCC) has concluded, ecosystems vital to human development and well-being are vulnerable to climate change. There are likely to be reductions in biological diversity and in the goods and services that ecosystems provide to society, e.g. sources of food, fibre, medicines, recreation and tourism, and ecological services such as controlling nutrient cycling, waste quality, water run-off, soil erosion, pollination services, detoxification and air quality. Additionally there may be an increased provision of ecosystem "bads" such as pests, diseases and other invasive species.

  • United Nations
  • United Nations Environment Programme