Green Wars are conflicts caused by environmental issues. Rampant overpopulation is causing obvious damage to the atmosphere, rivers, rain forests and is causing desertification, loss of habitat and species, and so on.
It is inevitable that this will lead to armed conflict, or Green Wars. The atmosphere belongs to all of us, not just China. Rivers flow through several countries; if California were still independent would they be happy about the trickle that was the mighty Colorado? Are you happy with the logging in the rainforests?
Early wars were for land. Later wars were for resources. Future wars may be fought to protect the environment. Hello, Green Wars.