Well, a good number of environmentalists would like to kill 90% of us off and the sooner the better. The climate will continue to change because that’s what it’s always done.
If we get rid of domesticated animals to help with the methane and outlaw the internal combustion engine, that should starve at least 50% of us. The remaining people will live such meager and cheerless lives that those not in power will lose their will to live.
The Algores of the world want to live like the Jetson’s all the while they want you an I to live like the Flintstones.
I consider radical environmentalists to be the group most likely to use homemade WMD on a large scale basis, specifically to kill as many people as possible. Many of them consider the human race to be a cancer on the planet. Many have advanced degrees in biological sciences. Many would die for their cause. I would not put it past them to steal and/or develop bioweapons and deploy them on a mass scale.