Answer:
Global warming
Explanation:
Global warming is defined as the long-term heating of Erath's system due to human activities.
The cause of both the problems spreading pine beetles and melting sea ice is common, that is "Global Warming".
Global warming is the major reason for unnecessary climate changes that allow pine beetles (tree-killing beetles) to produce two generation annually which were earlier producing only one generation annually.
Warming temperature in Global warming is allowing the melting of ice in glaciers or poles, which is a major environmental issue.
Hence, spreading pine beetles hand melting sea ice have global warming in common.
