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Climate Change, Ecosystems & Biodiversity

Introduction

The main objective of the UN Framework Convention on Climate Change is to stabilise greenhouse gas concentrations in the atmosphere at a level which will avoid dangerous human interference with the climate system. This should occur within a time frame that ensures the rate of climate change is slow enough to allow ecosystems to adapt naturally. Current levels of greenhouse gas emissions will cause climatic changes that many species and ecosystems will not be able to adapt to. This fact sheet looks at the impacts of climate change on ecosystems and on biodiversity.

Impacts of Climate Change on Ecosystems

During the 20th century, the global climate has warmed by about 0.6C. Computer models which simulate the effects on climate of increasing atmospheric greenhouse gas concentrations project that global average surface temperatures will rise by a further 1.4 to 5.8C by the end of the 21st century. It is currently believed that most ecosystems can withstand at most a 0.1C global temperature change per decade, before experiencing severe ecological stresses, leading in some cases to species extinction. A warming of even 2C over the next 100 years would shift current climate zones in temperate regions of the world poleward by about 300 km, and vertically by 300m. The composition and geographic distribution of unmanaged ecosystems will change as individual species respond to new conditions. At the same time, habitats will be degraded and fragmented by the combination of climate change, deforestation, and other environmental pressures.

Ecosystems under threat

Ecosystem Climatic variables influencing ecosystem
Tropical forest
  • Cloud cover and sunlight hours
  • Hurricane frequency / severity
  • Drought frequency
  • Annual rainfall distribution
  • Boreal forest  
  • Mean annual temperature
  • Fire frequency and severity
  • Storm frequency and severity
  • Growing season length
  • Arid and semi-arid areas
  • Precipitation patterns
  • Minimum winter temperatures
  • Low-lying islands
  • Relative sea-level rise
  • Storm frequency and severity
  • Arctic (ice) regions    
  • Mean annual temperature
  • Season length
  • Precipitation
  • Timing and extent of ice melt
  • Mountains
  • Mean annual temperature
  • Snow fall and melt
  • Growing season length
  • Wetlands
  • Mean summer temperature
  • Mean annual precipitation
  • Peat bogs
  • Mean summer temperature
  • Mean annual precipitation
  • Coastal marshes
  • Relative rate of sea-level rise
  • Storm frequency and severity
  • Coral reefs  
  • Relative rate of sea-level rise
  • Storm frequency and severity
  • Sea-surface temperature
  • The most vulnerable ecosystems will include those habitats where the first impacts are likely to occur, where the most serious adverse effects may arise, or where the least adaptive capacity exists. These include tropical and boreal forests, deserts and semi-deserts, low-lying islands, arctic regions, mountain systems, wetlands, peatbogs and coastal marshes, and coral reefs. Changes in other climatic variables, in addition to temperature, such as rainfall, sunshine, cloud cover, and the frequency and intensity of extreme events, will influence these vulnerable ecosystems. These are outlined in the table above.

    For some ecosystems, such as coral reefs and tropical forests, climate change is presently a low-level threat in comparison with current environmental pressures and degradation. In coming decades, as habitats decline and become more fragmented, and their communities less diverse, there is every likelihood that climate change will enhance existing stresses. As natural systems lose their resilience, the threat of climatic impacts will become more acute.

    With unmitigated emissions of greenhouse gases, substantial dieback of tropical forests and tropical grasslands is predicted to occur by the 2080s, especially in northern South America and central southern Africa. If emissions are reduced enabling atmospheric carbon dioxide concentrations to stabilise at 550 ppm (double the pre-industrial level), this loss would be substantially reduced, even by the 2230s. Considerable growth of forests is predicted to occur in North America, northern Asia and China.

    Biodiversity

    At the Earth Summit in 1992, over 150 Heads of State signed the Convention on Biological Diversity. They did so in order to initiate action to halt the world-wide loss of animal and plant species and genetic resources. An increasing threat to biodiversity - a combination of genetic variation, species richness, and ecosystem and landscape diversity - comes from climate change. Whilst significant scientific uncertainties surround its measurement, biodiversity at all levels today is probably being lost at an unprecedented rate. 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. Current rates of extinction from tropical forests alone have been estimated at 1-11 per cent per decade.

    Adaptation

    Since the birth of agriculture some 8,000 to 10,000 years ago, humans have had a significant influence of the Earth's ecosystems. It is therefore difficult to define natural adaptation. Instances of change need to be related directly to human activity. For example, the creation of Britain's woodland by the spread, over thousands of years, of birch, then oak, alder, and other tree species into moorland and tundra after the last glaciation provides an example of natural adaptation to natural climate change. However, the deforestation that destroyed approximately half of the this vegetation between about 6,000 and 2,000 years ago was largely caused by human development and agriculture. Species have evolved to cope with natural climate changes, and in some cases, the influences of mankind. It is doubtful, however, given today's globalised and ever-increasingly energy- and resource-consuming society, that ecosystems will be able to respond to climatic pressures, as they have managed to in the past. It is possible that by the end of the next century, rates of climate change will be at least an order of magnitude faster than at any time during the last 10,000 years and possibly the last 100,000 years.

    Conclusion

    As climate changes the composition and geographic distribution of many ecosystems will shift as individual species respond to changes in climatic variables. There will be likely reductions in biological diversity and in the goods and services which ecosystems provide society. Some ecological systems may not reach a new equilibrium for several centuries after the climate achieves a new balance. Some species within such ecosystems may become extinct.