He is chairing a virtual meeting of the 15-member council on climate-related risks to international peace and security.
"Think of a young man forced onto the road when his home becomes a desert... He goes to some camp, he becomes prey for violent extremists, people who radicalize him, and the effects of that radicalization are felt around the world," Johnson said.
With the world struggling to cut planet-warming emissions fast enough to avoid catastrophic warming, the United Nations will stage a climate summit in November in Glasgow, Scotland.
It will be the most important gathering since the 2015 event that yielded the Paris Agreement, when nearly 200 countries committed to halt rising temperatures quickly enough to avoid catastrophic change.
The November summit serves as a deadline for countries to commit to deeper emissions cuts.