Reading the intro, I had to laugh though. According to Army doctrine now, climate change is real. Paragraph 1-13. The debate is over.
I don't think anyone who is educated in the field denies climate change, the debate is over the cause. There is evidence of periods of climate in the earth's distant past, so it shouldn't be an overly difficult concept to grasp. We don't know if it is a relatively short term change, or a long term change that will have significant impacts.

The so what factor of it are the largely unknown impacts on agriculture (food supplies), water, rising sea levels potentially displacing large populations (to where?), etc. In theory the cause of war could shift back to the basics, access to resources (water, ariable land, etc.) required for survival, instead of being largely ideologocially focused.

Not exactly COIN, but think about it, our grand kids may not be focused so much on gaining legitimacy, but rather on eliminating the threat to our resources to ensure our survival.

I do find it odd that it is addressed in the COIN FM though. What was the context?