Understanding past climatic and environmental change is clearly relevant to predicting the future. This contention is not new (Alverson et al. 2000, 2003; Alverson and Kull 2003), but a few salient examples deserve highlighting here.
• The paleorecord extends instrumental climate records thereby increasing the statistical significance of documented anthropogenic change.
• Long-term processes in the paleorecord operating on timescales of decades to millennia are still occurring and will influence the present and the future as they have in the past.
• The paleorecord contains a much fuller representation of the range of climatic and environmental variability than do either the instrumental record or numerical models.
• The paleorecord abounds with large and abrupt climate changes.
• The paleorecord includes numerous examples of the interaction between climate change in ecosystems and even societies.
Growing attention has been paid to the possible ramifications of potential future abrupt shifts beyond the range of variability on which planning and construction schemes are based and even outside the envelope of scenario future projections generated by climate models. The record of climate variability back through time reveals that such changes, often sudden, and sometimes persistent on decadal to century timescales. By the very nature of nonlinear systems, which are marked by sensitive dependence on initial conditions, such abrupt changes will remain largely unpredictable, no matter how sophisticated coupled, dynamical climate models may become. Thus, the best way to account for them is to develop scenarios based on past events.
Examples of abrupt climate events in the paleorecord are not limited to Greenland or glacial periods. Hydrological variability such as that shown in O Figure 12.7, for example, includes sudden and high amplitude changes that can be persistent for decades to centuries. Such variability lies well outside the range of instrumental records. Concepts of future environmental sustainability, water supply, and food security are limited and potentially dangerously short sighted if they fail to accommodate such evidence, especially given that these records are from regions that today experiences widespread catastrophic human casualties following on just a few consecutive years of drought. Climate variability and environmental change have played a major role in the welfare of human societies in the past, and all current indications are that their significance may be even greater in the future. The combination of high vulnerability to environmental hazards, such as floods and droughts, and continuing rapid population growth leave parts of the region under serious threat from increased variability, extreme events and future sea-level rise. Climate variability affects human welfare in a variety of ways and on a range of spatial and temporal scales. Equally, as land cover and agricultural practices change in response to evolving human needs there are important feedbacks to the climate system. The paleorecord holds vital clues as to how these interactions work. Improving the quality and long-term security of water supplies, enhancing agricultural productivity, and planning for the avoidance or mitigation of environmental hazards are all of high priority for human societies, and they all require a good understanding of past variability, human responses, and human-environment interactions.
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