What was done
The authors reconstructed the Holocene environmental history of Kootenay Valley in the southern Canadian Rockies based on relevant data obtained from the sediments of Dog Lake, British Columbia (50°46'N, 116°06'W).

What was learned
In the centuries leading up to AD 800, Hallett and Hills report the development of "a more open landscape," and that "fire frequencies and summer drought appear to increase." This "increased fire activity," in their words, "is supported by higher dry-open/wet-closed [forest] pollen ratios and indicates a return to dry-open forest conditions around Dog Lake," which lasted about 400 years. Thereafter, they determined that "wet-closed forest cover reaches its maximum extent from 700-150 cal years BP [AD 1300-1850]" in what "appears to be a response to Little Ice Age cooling." Last of all, they say that "current global warming trends ... may again create the conditions necessary for dry-open ... forest to expand in the Kootenay Valley."

What it means
The likelihood that current global warming, in the opinion of Hallett and Hills, may recreate climatic conditions similar to those that prevailed in the Kootenay Valley prior to the global chill of the Little Ice Age suggests it has not been as warm there yet, nor for as long a time, as it was between AD 800 and 1200, when the Medieval Warm Period held sway in that part of the world. For this region, therefore, it would appear that the Current Warm Period cannot yet hold a candle to both the level and duration of medieval warmth, which their work suggests was unprecedented over the past millennium. And the fact that there was 100 ppm less CO2 in the air of that early record warm period than there is today suggests that something far more potent than the atmosphere's CO2 concentration is in control of earth's climate and the cause of 20th-century global warming.