7. Impacts of climate change on biodiversity and ecosystem services
Authors: Claire Brown (UNEP-WCMC), Robert Munroe (BirdLife), Climate Change Team (UNEP-WCMC), Stavros Papageorgiou (CI) and Jenny Birch (BirdLife)
In the last 100 years average global temperature has increased by 0.74°C, rainfall patterns have changed and the frequency of extreme events increased. Change has not been uniform on either a spatial or temporal scale and the range of change, in terms of climate and weather, has also been variable.
Change in climate has consequences on the biophysical environment such as changes in the start and length of the seasons, glacial retreat, decrease in Arctic sea ice extent and a rise in sea level. These changes have already had an observable impact on biodiversity at the species level, in term of phenology, distribution & populations, and ecosystem level in terms of distribution, composition & function.
Many changes have been reported in the distribution of species. In general, many species have expanded their ranges poleward in latitude and upward in elevation. Evidence of contraction in species’ distribution is limited, however, possibly due to reporting difficulties and time lag in such contractions due to a wide variety of possible mechanism such as population dynamics. Populations of many species have declined, and although in some cases climate change is believed to have contributed to the decline, attributing this is fraught with difficulty as it is likely to be only one driver amongst many. At the species level, changes observed that can be attributed to climate change involve those surrounding phenology (the timing of events). Many birds and insects are showing changes, such as earlier onset of migration, egg-laying and breeding. In terms of ecosystems, there has been some evidence on changes in distribution. e.g. desert ecosystems have expanded, and tree lines in mountain systems have changed. Changes in the composition of ecosystems have also been observed (e.g. increased lianas in tropical forest). Such changes may affect ecosystem function and the ecosystem services they provide. Changes in biodiversity and ecosystem services due to climate change are not all negative, with some species either thriving or adapting.
Most of these observed changes are modest, which is possibly due to the limited change in climate that has occurred. However, future projected changes in climate are much larger. IPCC AR4 suggests that approximately 10% of species assessed so far will be at an increasingly high risk of extinction for every 1°C rise in global mean temperature, within the range of future scenarios modelled in impacts assessments (typically <5°C global temperature rise). Aquatic freshwater habitats and wetlands, mangroves, coral reefs, arctic and alpine ecosystems, and cloud forests are particularly vulnerable to the impacts of climate change. Montane species and endemic species have been identified as being particularly vulnerable because of narrow geographic and climatic ranges, limited dispersal opportunities, and the degree of non-climate pressures. Potential impacts of climate change on genetic diversity are little understood, though it is thought that genetic diversity will increase the resilience of species to climate change.
Modelling studies on the potential impact of climate change on species indicates poleward shifts and changes in altitude, range expansions or contractions corroborating the current evidence in the most part. However, such studies highlight the individualistic nature of species’ responses to climate change, which is likely to have a large impact on future composition of ecosystems. Structure of ecosystems may also change. Models suggest this may have an impact on ecosystem function. For example, modelling suggests increases in net primary production in northern Europe but decreases in areas where water is a limiting resource. Changes in productivity are likely to change services such as nutrient cycling due to changes in litter fall. Other potential changes to ecosystem services due to climate change, include changes to the provisioning services (e.g. food, fibre, timber), carbon storage and sequestration, water regulation and disease regulation.
Changes to ecosystems as a result of climate change are likely to have significant and often negative social, cultural and economic consequences. However, there is still uncertainty about the extent and speed at which climate change will impact biodiversity and ecosystem services, and the thresholds of climate change above which ecosystems are irreversibly changed and no longer function in their current form. Tipping points are points at which a system passes from one steady state to another. These are used for either climate tipping points or ecosystem tipping points. An example of the latter is Amazon forest dieback.
There are several methods and tools to assess the impact of climate change on biodiversity and ecosystem services. Vulnerability assessments have particular meaning in the natural hazards and socio-economic fields but are used more loosely and encompass a variety of methods in the field of biodiversity and climate change. Climate envelope modelling is by far the most common tool used to assess potential impacts (and to infer vulnerability) on species. Although these suffer a number of limitations, they do provide a first cut assessment of the likely magnitude and direction of change. Dynamic models, population models and mechanistic models are other modelling tools that have been used to assess future impact and vulnerability on both species and ecosystems, though ecosystem service modelling is still in its infancy. These latter models need to become more prominent as climate envelop modelling mainly provide species exposure to climate change and thus only one facet of vulnerability. Indeed vulnerability is defined as a function of exposure, sensitivity and adaptive capacity.
Mismatches evidenced in Europe between caterpillar emergence and the timing of breeding of a long-distance migrant bird has led to population declines. Both, C., Bouwhuis, S., Lessells, C.M., and Visser, M.E. (2006) Climate change and population declines in a long-distance migratory bird. Nature, 441: 81-83.
Long term monitoring and dynamic modelling suggests a continuing in carbon sequestration service of Amazonian forests in the short to medium term but that this service may be reversed in the longer term due to increases in temperature. Phillips, O.L., Lewis, S.L., Baker, T.R., Chao, K.J. and Higuchi, N. (2008) The changing Amazon forest. Phil. Trans. Royal Soc.B-Biol. Sci. 363: 1819-1827.
- How does one determine and understanding ecosystem tipping points?
- How does one attribute observed changes in biodiversity ecosystem services to climate change?
- How can one realistically predict the impacts of climate change on biodiversity?
- How does one model the potential impacts of climate change on ecosystem services?
- How does one detail insight into sensitivity and adaptive capacity as elements of assessing vulnerability of biodiversity and ecosystem services to climate change?
Climate envelope models or species distribution models
Climate vulnerability assessments:
- http://www.unep.org/pdf/IEA_climate_change.pdf (supported by examples and exercises, the module describes the process for addressing climate change in the context of other development priorities and ecosystems to help decision-makers move towards more sustainable development pathways and ecosystem resilience.)
- http://www.ipcc-data.org/guidelines/TGICA_guidance_sdciaa_v2_final.pdf (general guidelines on the use of scenario data for climate impact and adaptation assessment)
- http://www.natureserve.org/prodServices/climatechange/ccvi.jsp (using the Index, you apply readily available information about a species’ natural history, distribution and landscape circumstances to predict whether it will likely suffer a range contraction, population reductions, or both during the coming years)
- Glick, P., B.A. Stein, and N.A. Edelson, editors, 2011. Scanning the Conservation Horizon: A Guide to Climate Change Vulnerability Assessment. National Wildlife Federation, Washington, D.C. (designed to help conservation practitioners understand how vulnerability assessments can help them in responding to the challenges of managing natural resources in an era of climate change.)
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Photo credit: Jim Maragos/U.S. Fish and Wildlife Service; flickr.com