This is a bit difficult to think about, and to read about it as documents that refer to some major 1st world countries (countries with a lot of power and money) is not good. But I will keep my opinion limited here,
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Memorandum, The White House, James. B. Steinberg, et al., to President Clinton, Subject_ Climate Change_Military, March 3, 1998 [Classification Unknown] _ National Security Archive
Pentagon Fuel Use, Climate Change and the Costs of War Revised November 2019 Crawford