| 1. |
- Callaghan, Terry V., et al.
(author)
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Climate Change and UV-B Impacts on Arctic Tundra and Polar Desert Ecosystems: Key Findings and Extended Summaries
- 2004
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In: Ambio: a Journal of Human Environment. - 0044-7447. ; 33:7, s. 386-392
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Journal article (peer-reviewed)abstract
- The Arctic has become an important region in which to assess the impacts of current climate variability and amplification of projected global warming. This is because i) the Arctic has experienced considerable warming in recent decades (an average of about 3°C and between 4° and 5°C over much of the landmass); i) climate projections suggest a continuation of the warming trend with an increase in mean annual temperatures of 4–5°C by 2080; ii) recent warming is already impacting the environment and economy of the Arctic and these impacts are expected to increase and affect also life style, culture and ecosystems; and iv) changes occurring in the Arctic are likely to affect other regions of the Earth, for example changes in snow, vegetation and sea ice are likely to affect the energy balance and ocean circulation at regional and even global scales (Chapter 1 in ref. 1). Responding to the urgent need to understand and project impacts of changes in climate and UV-B radiation on many facets of the Arctic, the Arctic Climate Impact Assessment (ACIA) (1) undertook a four-year study. Part of this study (1–10) assessed the impacts of changes in climate and UV-B radiation on Arctic terrestrial ecosystems, both those changes already occurring and those likely to occur in the future. Here, we present the key findings of the assessment of climate change impacts on tundra and polar desert ecosystems, and xtended summaries of its components.
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| 2. |
- Callaghan, Terry V., et al.
(author)
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Effects of changes in climate on landscape and regional processes, and feedbacks to the climate system
- 2004
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In: Ambio: a Journal of Human Environment. - 0044-7447. ; 33:7, s. 459-468
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Research review (peer-reviewed)abstract
- Biological and physical processes in the Arctic system operate at various temporal and spatial scales to impact large-scale feedbacks and interactions with the earth system. There are four main potential feedback mechanisms between the impacts of climate change on the Arctic and the global climate system: albedo, greenhouse gas emissions or uptake by ecosystems, greenhouse gas emissions from methane hydrates, and increased freshwater fluxes that could affect the thermohaline circulation. All these feedbacks are controlled to some extent by changes in ecosystem distribution and character and particularly by large-scale movement of vegetation zones. Indications from a few, full annual measurements of CO2 fluxes are that currently the source areas exceed sink areas in geographical distribution. The little available information on CH4 sources indicates that emissions at the landscape level are of great importance for the total greenhouse balance of the circumpolar North. Energy and water balances of Arctic landscapes are also important feedback mechanisms in a changing climate. Increasing density and spatial expansion of vegetation will cause a lowering of the albedo and more energy to be absorbed on the ground. This effect is likely to exceed the negative feedback of increased C sequestration in greater primary productivity resulting from the displacements of areas of polar desert by tundra, and areas of tundra by forest. The degradation of permafrost has complex consequences for trace gas dynamics. In areas of discontinuous permafrost, warming, will lead to a complete loss of the permafrost. Depending on local hydrological conditions this may in turn lead to a wetting or drying of the environment with subsequent implications for greenhouse gas fluxes. Overall, the complex interactions between processes contributing to feedbacks, variability over time and space in these processes, and insufficient data have generated considerable uncertainties in estimating the net effects of climate change on terrestrial feedbacks to the climate system. This uncertainty applies to magnitude, and even direction of some of the feedbacks.
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| 3. |
- Callaghan, Terry V., et al.
(author)
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Synthesis of effects in four Arctic subregions
- 2004
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In: Ambio: a Journal of Human Environment. - : Royal Swedish Academy of Sciences. - 0044-7447. ; 33:7, s. 469-473
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Journal article (peer-reviewed)abstract
- An assessment of impacts on Arctic terrestrial ecosystems has emphasized geographical variability in responses of species and ecosystems to environmental change. This variability is usually associated with north-south gradients in climate, biodiversity, vegetation zones, and ecosystem structure and function. It is clear, however, that significant east-west variability in environment, ecosystem structure and function, environmental history, and recent climate variability is also important. Some areas have cooled while others have become warmer. Also, east-west differences between geographical barriers of oceans, archipelagos and mountains have contributed significantly in the past to the ability of species and vegetation zones to relocate in response to climate changes, and they have created the isolation necessary for genetic differentiation of populations and biodiversity hot-spots to occur. These barriers will also affect the ability of species to relocate during projected future warming. To include this east-west variability and also to strike a balance between overgeneralization and overspecialization, the ACIA identified four major sub regions based on large-scale differences in weather and climate-shaping factors. Drawing on information, mostly model output that can be related to the four ACIA subregions, it is evident that geographical barriers to species re-location, particularly the distribution of landmasses and separation by seas, will affect the northwards shift in vegetation zones. The geographical constraints-or facilitation-of northward movement of vegetation zones will affect the future storage and release of carbon, and the exchange of energy and water between biosphere and atmosphere. In addition, differences in the ability of vegetation zones to re-locate will affect the biodiversity associated with each zone while the number of species threatened by climate change varies greatly between subregions with a significant hot-spot in Beringia. Overall, the subregional synthesis demonstrates the difficulty of generalizing projections of responses of ecosystem structure and function species loss, and biospheric feedbacks to the climate system for the whole Arctic region and implies a need for a far greater understanding of the spatial variability in the responses of terrestrial arctic ecosystems to climate change.
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