Climate Change's Role

Background on Climate Change

Mountain pine beetles have existed in western North America for millions of years and have played an important role in the ecosystem of western North America (Sambaraju et al. 2011).  Mountain pine beetles usher in renewal of forest by killing older, less healthy trees thereby allowing younger trees to take their place.  However, outbreaks and epidemics of tree death caused by the beetles have increased dramatically over the past 40 years.  North American forests are currently experiencing a large and severe epidemic of tree death caused by mountain pine beetles.  Some estimates have total tree death due to mountain pine beetles at eight million acres in the United States alone (Frost 2011).  Why are mountain pine beetles so detrimental to the forest ecosystems now?  A hypothesized cause of the accelerated propagation of mountain pine beetles is climate change.

Climate change observed currently is predominantly
caused by human activities (Courtesy of the EPA)

Climate change is occurring throughout the world.  A main cause of climate change is attributed to the worldwide usage and burning of fossil fuels.  Fossil fuels are essentially carbon that is burned to produce energy.  The burning of fossil fuels produces several byproducts, one of which is carbon dioxide.  Fossil fuel burning is heavily relied upon for energy which has led to exorbitant release of carbon dioxide into the atmosphere.  According to the Environmental Protection Agency, "Atmospheric CO2 concentrations have increased by almost 40% since pre-industrial times, from approximately 280 parts per million by volume (ppmv) in the 18th century to 390 ppmv in 2010. The current CO2 level is higher than it has been in at least 800,000 years" (EPA).  This influx of carbon dioxide has resulted in more atmospheric carbon and ultimately a stronger greenhouse effect.  A stronger greenhouse effect has led to higher temperatures around the world, including western North America (EPA).

Climate Change and Mountain Pine Beetles

Naturally, populations of beetle fluctuate due to natural temperature variations between years.  Cold winters are the essential mechanism for preventing mountain pine beetle populations from getting out of hand.  However, global temperatures are expected to continue rising with estimates ranging from 1.1 to 6.4°C (Sambaraju et al. 2011).  Beetle ranges may shift due to rising temperatures.  It has been demonstrated that temperatures below -40°C result in 100% mortality of beetles (Sambaraju et al. 2011).  However, if boreal regions in northern Canada fail to reach temperatures as low at -40°C, then mountain pine beetles may spread to boreal pine trees exacerbating tree death in western North America (Sambaraju et al. 2011).  Range shifts may have already begun because mountain pine beetles have been detected at higher elevations and northern regions and are already experiencing population fluctuations (Powell and Raffa 2011).

Feedback loop of climate change and mountain pine beetles
(+) indicates positive effect, (-) indicates negative effect
(Original image)

Accordingly, rising global temperatures estimates have led to predictions about future beetle populations.  Mountain pine beetle death due to cold temperatures may decrease 69-87%, resulting in more beetles (Sambaraju et al. 2011).  More beetles means more tree death.  This increase in tree death has contributed to increased risk of forest fires (Frost 2011).  A surge in the number of forest fires may introduce more CO2 into the atmosphere which will produce a positive feedback and leading to more pronounced climate change.

Climate change is expected to usher in decreased precipitation which will lead to droughts (Sambaraju et al. 2011).  Increased drought events are expected to increase the amount of wildfire events which negatively effect pine tree populations.

Rising temperatures due to climate change are likely the main reason why mountain pine beetles are propagating in record numbers.  Without drastic reductions to worldwide greenhouse gas emissions, global temperatures will continue to rise.  It is likely that mountain pine beetles will continue their march northwards and vertically.  Until major reductions in greenhouse gas emissions are realized, prevention and management efforts will be the best way to cope with mountain pine beetle infestations.