Decoding Canada's Environmental Past

A tremendous wealth of information about our biological and climatological past is locked in our environment. Everything from tree rings and lake sediments to insect fossils and glacial ice caps contains clues about historical trends and extremes, and how our ecosystems adapted to them.

Scientists are using these clues, along with human records such as aboriginal pictographs, Hudson's Bay Company reports and meteorological data, to predict the impacts of climate change in the coming millennium. Environment Canada is helping to solve the puzzle by bringing together Canadian and American experts from a wide range of disciplines to share their knowledge at an ongoing series of targeted workshops on Decoding Canada's Environmental Past.

These workshops focus on the use of paleo, or historical, human and natural records, to reconstruct variations in our climate and biodiversity during the last thousand years, and examine the different ways our environment has adapted or responded to these changes. Using major climate events as marker years to align their data, scientists from universities, museums and government agencies have issued surprisingly common messages about the impacts of climate change in Canada, where the effects of a changing climate are already being felt in many regions.

Tree rings are a rich source of paleo information, because ring growth is significantly influenced by climate. A recent study on Vancouver Island showed that 60 per cent of the ring-width variance in mountain hemlock could be attributed to climate variables in the previous year. High-elevation stands of mountain hemlock and yellow cedar have proven particularly good indicators, because the extreme nature of their environment makes them highly sensitive to climatic fluctuations. And, because many mature trees of both species exceed 500 years in age, they can yield long-term information. A study of old-growth mountain hemlock in Strathcona Provincial Park, on Vancouver Island, revealed a close correlation between significant intervals of reduced ring growth and the climatic episodes of the Little Ice Age, which reached its peak in the 18th to 19th centuries. These same periods coincided closely with significant moraine-building episodes and glacial advances.

Another study of mountain hemlock growth trends and El Niño events on Vancouver Island since 1500 shows that periods of increased El Niño frequency generally correspond to intervals of enhanced ring-width growth. Hundred-and-fifty-year records from Saanich Inlet also suggest an increase in the frequency of strong El Niños in the future, and show a correlation between such events and outbreaks of the toxic aquatic organisms that cause red tides. Related to these increasing events is the recent discovery that shifts between climate states have occurred repeatedly and often abruptly in the past—most recently in 1976—with significant repercussions for fisheries, water resources, forestry, agriculture and habitats.

Both records of pollen ratios in lake sediment and tree-ring density in northwestern Canada between 1650 and 1990 show summer temperatures in the region on a gradual rise over the past four centuries. A comparison of these results with the reconstruction of white spruce establishment and mortality patterns at alpine treeline sites in the western Northwest Territories and central Yukon shows that the effects of this warming trend include a significant increase in tree population density, but only a minor advance in the treeline.

Tree-ring density records from northern Canada for the last 400 years indicate that devastatingly cold temperatures have been experienced in different regions of North America in the year following a major volcanic eruption—proof that major events, even in other parts of the world, can have a profound impact on geographically distant environments. Because the sulphate aerosols emitted by volcanoes are similar to, but at much higher concentrations than, those released by many manmade sources today, increasing levels of pollution may have a similar cooling effect on future temperatures.

Lakes are also used to reconstruct past climate and biological changes. Studies in the southern prairies of Canada indicate that the most sensitive lakes display water-level changes that are broadly correlative with well-known hemispheric-scale climatic events. The abundance of pollen buried in lake sediments enables s cientists to estimate climate changes, while pollen composition tells us how these changes have affected biodiversity. Synthesizing data from these sites can also suggest how atmospheric circulation has changed. Microscopic charcoal fragments in lake sediments can be used to reconstruct post-glacial fire incidence, and provide insight into changes in distribution, biodiversity and fire activity of forest ecosystems under a global warming scenario.

While ecosystem shifts tend to follow climate change, rather than precede it, insects serve as important "bell ringers" that forewarn us of changes to come. Fossils of aquatic midge larvae have recently been developed as quantitative indicators of past climatic changes, and provide a sensitive independent climate record for southern British Columbia. About 10 000 years ago, a sudden increase in the abundance of warm-water species was followed by a rapid 5°C increase in summer temperatures. In the dry interior valleys of southern British Columbia, the immigration of salt lake species records the shift from a humid to a semi-arid climate.

This graph shows the close correlation between El Niño events and the growth of mountain hemlock from 1500 to 2000.

Three different sets of data were used to examine past winter severity in the Great Plains region. Using aboriginal pictographic winter counts time-aligned by meteorological and pictographic evidence of a major meteor shower in 1833, researchers found that the length of time between severe winter episodes decreased between the 1680s and the 1880s, with bad winters especially prevalent during the 1800s. Studies of population density of white-tailed deer and pronghorn antelope on the margins of their ranges showed a close correlation between decreased numbers and severe winters, while bison remains reflected these seasonal stresses in tooth enamel formation.

Studies of climate signals locked in our environmental past also tell us how the impacts of human activities, combined with those of climate change, could affect our environment in the future. For example, the drastic human alteration of the prairie grasslands for agricultural purposes during the early part of this century combined with drought conditions to cause the catastrophic dust storms of the 1920s and 30s—with the insect populations still in a state of disequilibrium 60 years later. Had the biodiversity and root mass of the grassland ecosystem been left intact, they would have greatly reduced the impacts of this disaster, which resulted in billion-dollar losses to this dust-bowl region of Canada.

Similar lessons emerge from human observation records of the flood and runoff histories of the Red River Basin from the late 18th century onward, which suggest that the Great Plains may have had a hydroclimatically wetter environment during much of the 19th century—when several major floods occurred in 1826 and 1852. Combining these data with geographical studies of the current flood plain—which has been dramatically altered by human development during the 20th century—indicates that if floods of this magnitude were to occur today, their effects would be even more devastating than those of the 1997 Red River flood. With severe weather events expected to increase as a result of climate change, the possibility of such a situation occurring is far from remote.

Understanding that natural atmospheric processes are ongoing and how they minimize or exacerbate the effects of human activities on the environment is essential to reducing our vulnerability to climate variability and change in the coming millennium. Next year's workshop, on integrated mapping, will add yet another chapter to our understanding of the correlation between climate and biodiversity, and further improve the effectiveness of our adaptation strategies.

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