It is known that mountain pine beetle infestations have the potential to raise nearby air temperatures by killing off trees that provide a natural refrigerator effect for forests.
Now, researchers are releasing hard numbers documenting how the pests' invasions affected a specific place.
In a study published in Nature Geoscience, scientists at the University of Toronto and the University of California, Berkeley, reported that the beetle scourge in British Columbia raised surface temperatures in affected areas by 1 degree Celsius on average in the summer. In the worst-hit areas where provincial forests were wiped out, the summer temperature increase was several degrees higher.
"Previous studies have shown that climate change has allowed the beetle to flourish. Our work shows that beetle infestations in turn feed back on climate, creating yet warmer summertime temperatures," said Holly Maness, a study co-author and a postdoctoral fellow in the department of earth and planetary science at UC Berkeley.
When the numbers are scaled provincewide, the beetle infestations likely raised temperatures on average by half a degree Celsius, even outside forested areas, she said. The scientists examined the period between 1999 and 2010, using satellite and provincial forest data.
The work is distinctive because it translates theory to a specific and very large region, according to Maness. It also raises questions about how beetle infestations may affect precipitation patterns in Canada, she said.
The team found that bark beetle infestations increased outgoing heat in the forests -- via air flows -- by roughly 8 percent. This could interact with cloud formations, Maness said, although the exact way the 8 percent increase could influence weather, air circulation and precipitation is not fully understood.
Outgoing forest heat via radiation "fluxes" increased by 1 percent in beetle-infested areas, the study said.
Warming effect larger than that of forest fires
In addition, the scientists found that bark beetle infestations reduced total forest evaporation by 19 percent on average in the summer, Maness said. The team accounted for natural fluctuations in temperature.
Another reason "we are confident in the findings" is that temperatures went up more in areas with more killed trees, Maness said.
She added that the reason beetles are driving the temperature up, and evaporation down, is relatively simple.
Trees produce a natural "sweat" by sending water from their roots to their leaves, she said. That water is then evaporated typically via sunlight. The evaporation process creates a cooling effect, because the sun's radiation, in essence, is used for something other than heating the Earth's surface.
When the trees die because of beetle infestations, the sun's heat then causes surface temperatures to rise more than they would otherwise.
Milder winters fueled by climate change drive the process, she said, because cold weather kills mountain pine beetle eggs. Hot and dry summers also stress pine trees, making them more susceptible to attack.
The warming effect of beetle kills is similar to what happens with wildfires, according to the study.
"Although the observed consequences ... are similar to those reported in the case of fire, the size of typical wildfires is much smaller than that of the present mountain pine beetle infestation," the study states.
'A major hit' to timber industry
Mountain pine beetle attacks over the past decade have affected 66,000 square miles, or 20 percent of the province's area .
According to official British Columbia documents, the infested area is now more than five times the size of Vancouver Island. The provincial government has committed more than $884 million to fight the pests. By 2021, 58 percent of the province's volume of pines could be killed, according to the government.
"The timber industry is taking a major hit," said an official in the British Columbia Ministry of Forests, Lands and Natural Resource Operations. The industry is grappling with employment issues in sawmill towns with a lower supply of trees, the official said.
One of the main strategies right now is replanting, the official said, and conducting research on how to better protect new trees. Last month, the province released an action plan titled "Beyond the Beetle" calling for new legislation and forest management practices.
There are concerns about beetles moving into new areas in Canada as well. In October, for example, the Saskatchewan government announced a $240,000 contract to protect Cypress Hills Interprovincial Park, saying beetle populations have been steadily increasing in the province.
"Left unmanaged, [the mountain pine beetle] could have devastating results," Saskatchewan Parks, Culture and Sport Minister Kevin Doherty said then in a statement.