Climate Change 2001: Synthesis Report

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Biodiversity, Agriculture and Forestry, and Climate Change


Changes in terrestrial and marine ecosystems are closely linked to changes in climate and vice versa. Changes in climate and in atmospheric concentrations of CO2 cause changes in the biodiversity and function of some ecosystems. In turn, ecosystem changes influence the land-atmosphere exchange of greenhouse gases (e.g., CO2, CH4, and N2O) and of water and energy, and change surface albedo. Therefore, understanding these combined effects and feedbacks are a requisite for evaluating the future state of the atmosphere and the natural systems and their biodiversity.

WGI TAR Section 4.5.3
8.14 Natural climate variations have illustrated the impacts of climate change on natural and managed ecosystems. The impacts of floods, droughts, and heat waves are etched into human history. Further, the warming events associated with El Niño illustrate that changes in climate patterns adversely affect fish, marine mammals, and coastal and ocean biodiversity. Coastal ecosystems -- such as coral reefs, salt marshes, and mangrove forests -- are affected by sea-level rise, warming ocean temperatures, increased CO2 concentrations, and changes in storm frequency and intensity. Table 8-1 gives main implications of climate change for natural ecosystems at the regional scale.

WGII TAR Chapters 5 & 6
8.15 Climate change is but one of many stresses on managed and unmanaged ecosystems. Land-use change, resource demands, deposition of nutrients and pollutants, harvesting, grazing, habitat fragmentation and loss, and invasive species are major stressors on ecosystems. They can lead to species extinction, resulting in losses of biodiversity. Therefore, climate change constitutes an additional stress and could change or endanger ecosystems and the many services they provide. As a result, the impact of climate change will be influenced by management of natural resources, adaptation, and interaction with other pressures. Figure 8-2 exemplifies the manner in which climate change interacts with other factors in food supply and demand.

WGII TAR Chapters 5 & 6, & WGIII TAR Sections 4.1-2
8.16 Climate change can influence the distribution and migration of species in unmanaged ecosystems. Populations of many species are already threatened with extinction and are expected to be placed at greater risk by the stresses of changing climate, rendering portions of their current habitat unsuitable. Vegetation distribution models since the SAR suggest that a mass ecosystem or biome movement is most unlikely to occur because differerent species have different climate tolerance and different migration abilities, and are affected differently by the arrival of new species. Lastly, in a related sense, climate change can enhance the spreading of pests and diseases, thereby affecting both natural ecosystems, crops, and livestock (e.g., changes in temperature and humidity thresholds allow pests and diseases to move to new areas).

WGII TAR Chapter 5
8.17 Carbon storage capacities of managed and unmanaged ecosystems, particularly forests, influence impacts and feedbacks with climate change. For example, forests, agricultural lands, and other terrestrial ecosystems offer a significant carbon mitigation potential. Although not necessarily permanent, conservation and sequestration may allow time for other options to be further developed and implemented. Terrestrial ecosystem degradation may be exacerbated by climate change, affecting the storage of carbon, and adding to the stresses resulting from the current deforestation practices. It should be noted that, if appropriate management practices are not carried out, CO2 emissions in the future could be higher. For example, abandoning fire management in forests or reverting from direct seeding to intensive tillage in agriculture may result in rapid loss of part, at least, of the accumulated carbon. WGIII TAR Section 4.3 & SRLULUCF SPM

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