The photo provided is courtesy of the Mine Safety and Health Administration. It shows a coal miner in the early 1900s with a canary in a cage.
These birds, preferred over mice, were used to alert underground miners to the presence of carbon monoxide, a toxic gas. The birds became visibly distressed in the presence of small amounts of this gas and provided a warning to the miners.
Today, observations suggest we have the equivalent of a new canary in a cage, this one for detecting climate change: the presence of billions of dead trees in the North American West.
The cause is the mountain pine beetle. This little creature has been around the American and Canadian West for a long time, but in small numbers. They were held in check by winter temperatures that frequently dropped to minus 40 degrees.
But temperatures do not get that low anymore, and more beetles survive the winter. With warmer temperatures, their life cycle speeds up, and they can produce more than one generation in a season. Their population has exploded.
A photo from the Vancouver Sun newspaper shows a pine beetle entering a small, round hole in the bark, where it gains access to the tree's nutrients. When the beetle numbers are high, the tree slowly starves and dies. According to the article, heavily forested British Columbia has lost about half its commercial forests in the past 15 years.
Photographs on the Web of forests damaged by these beetles are startling.
The whole issue is nuanced, however, with other factors merging into what appears to be a perfect storm in terms of climate change. Many parts of the West are also experiencing a drought. This weakens a tree and makes it more difficult for it to fend off insect attacks by producing extra sap to plug the holes. In addition, warmer summer weather reduces the life of the mountain snowpack, with less water available later in the season. This combination is proving deadly to a large swath of the West's forests.