Examine bark beetle outbreaks from a systems perspective

What caused the recent unprecedented bark beetle outbreaks in North America? Scientists suggest rising temperatures and droughts have significantly impacted the bark beetles, their host trees and their interactions.  

Research shows the average global temperature has risen about 1 degree Celsius since the industrial revolution. Specifically, a 0.6-0.7 degree Celsius increase has been observed in the past thirty years (Figure 14), which correlates with the increase in bark beetle outbreaks. Lab experiments have found that higher temperature may accelerate the bark beetle's life cycle, allowing them to reproduce earlier. Meanwhile, shorter and warmer winters allow more bark beetles and their larvae to survive the cold months. Both impacts of rising temperatures contribute to the growth of the bark beetle population. 

Many areas in the USA have been experiencing severe droughts over the past two decades (Figure 15). Normally, trees produce resin to fight off beetles and other pests. During a drought, trees experience water stress, which weakens their health and limits their ability to produce enough resin to defend themselves effectively. This makes it easier for bark beetles to infest the trees. 

A half degree Celsius increase does not sound like a big change. However, a small impact often produces a big effect in a complex system. Let's explore this using the computer model.