RAPID CLIMATE CHANGE AND SOCIETY: LESSONS FROM THE PAST, FOR THE FUTURE

Climate scientists have been monitoring the climatic impacts of the recent increase in greenhouse gas concentrations. The most important questions now facing scientists and policy makers are not related to whether climate change is occurring but rather the extent and rate of climate change and the consequent impacts on ecosystems, agriculture, and humans. Climate strongly controls human activities, economics, health, and national stability—one has to look no further than the collapse of the Mayan civilization for a lesson that climate change can lead to a cascade of effects that have a collective impact far exceeding the initial cause. If the Mayans had realized that their growth was pushing soil resources and food production capability to the climatic brink, they might have implemented more sustainable agricultural practices and survived what was actually a very subtle shift toward drier conditions but which had catastrophic effects.

To elucidate an example of rapid climate change that is perhaps relevant to the future, we focus on a cooling event that occurred about 8,200 years ago. Significant cooling at this time was first interpreted from ice core and marine records, with the suggestion that subtle changes in north Atlantic circulation (such as some have projected to occur over the next 50 years) caused extreme changes in temperature. Several recent studies have shown that the temperature effect was not restricted to the north Atlantic region, and also had profound effects on terrestrial landscapes. Our analysis of lake sediment core records from far western Canada reveals cooling and a rapid glacial readvance that is coupled with a change in soil nutrient status and ecosystem changes at 8,200 ybp. These findings collectively support the hypothesis that this cold event was sufficient in magnitude to have had a hemispheric and perhaps even global impact. Albeit “temporary” on geologic timescales, one can imagine the catastrophic effects of several centuries of cooling on agricultural and energy industries, particularly as this would come at a time when societies are bracing for general warming. One strategy for minimizing these impacts is to carefully measure north Atlantic circulation patterns and develop more sophisticated models of circulation-temperature coupling that are tied with the geologic evidence left over from the 8,200 year event.