Key Findings, Science Gaps and Policy Recommendations

Abstract

In general, changes in climate and UV in the Arctic will have far-reaching impacts, affecting aquatic species of varying trophic levels, the physical environment that makes up their habitat and the chemical properties of that environment, and the processes that act on and within freshwater ecosystems. Interactions of climatic variables such as temperature and precipitation with freshwater ecosystems are highly complex and can be propagated through the ecosystem in ways that are not readily projectable. This reduces our ability to accurately forecast specific effects of climate and ultraviolet-radiation change upon freshwater systems. This is particularly the case when dealing with threshold responses, i.e., those that produce step-wise and/or non-linear effects. Our ability is further hampered simply by our poor understanding of Arctic freshwater systems and their basic interrelationships with climatic and other environmental variables, as well as by a paucity of long-term freshwater monitoring sites and integrated hydroecological research programs in the Arctic. A significant amount of the understanding of potential impacts is based on historical analogues (i.e., historical evidence from past periods of climate change), as well as from a limited number of more recent studies of ecosystem response to environmental variability. Paleoreconstructions indicate that during the most recent period of climatic warming, which followed the Little Ice Age, the Arctic reached its highest average annual temperatures observed in the past 400 years, resulting in glacier retreat, permafrost thaw, and major shifts in freshwater ecosystems. Examples of ecosystem effects included altered water chemistry, changes in species assemblages, altered productivity, and an extended growing-season length. Importantly, however, past natural change in the Arctic occurred at a rate much slower than that projected for anthropogenic climate change over the next 100 years. In the past, organisms had considerable time to adapt; their responses may therefore not provide good historical analogues for what will result under much more rapid climate change. In many cases, the adaptability (i.e., adaptation, acclimation, or migration) of organisms under rapidly changing climate conditions is largely unknown. Unfortunately, no largescale attempts have been made to study the effects of rapid climate change on aquatic ecosystems using controlled experiments, as have been attempted for terrestrial systems (e.g., see International Tundra Experiment studies of tundra plant response in (1). However, field studies in areas that have recently experienced rapid changes in climate have provided important knowledge. Information about ongoing climate change impacts is provided by results from long-term environmental monitoring and research sites in the Arctic, including the case studies used in this assessment (i.e., Northern Quebec and Labrador, Canada (see 2), Toolik Lake, Alaska and Lake Saanajarvi, Finnish Lapland (see 3), and the Zackenberg Valley in northeastern Greenland (see 4).