Hordes of mountain pine beetles are decimating British Columbian forests. Rising temperatures due to global warming have boosted the beetles' numbers by increasing their reproductive rate and reducing their winter die-off.
Now, in a perverse twist, a new study shows that in a few years, the pests will have turned the once climate-friendly forests into net emitters of carbon dioxide (CO2).
Since 2000, the beetles have killed off more than 32 million acres of forest, according to Werner A. Kurz and a team of scientists from the Canadian Forest Service. Kurz and colleagues say the current outbreak is an order of magnitude larger than any previous mountain-pine-beetle explosion, and they predict it will take another twelve years or so to taper off.
That's a lot of dead trees, which release CO2 as they decompose. Meanwhile, there are fewer healthily growing trees left to absorb the greenhouse gas through photosynthesis.
Using a computer model, Kurz's team calculated that by 2020, the beetles will have killed so much forest that their net effect will be the equivalent of five years of CO2 emissions by all the cars and trucks of Canada.
Kurz and his team are the first to account for large-scale insect outbreaks in an analysis of forest carbon balances — and to show the positive feedback loop between climate change and insect pests. They're unlikely to be the last, however, given the risk of more boreal forests falling prey to warmth-loving insects.
The research was detailed in the journal Nature.