>They’re just talking about destroying its ability to sustain life
You should really look deeper into the effects of large historical asteroid impacts and other major cataclysms. Literally, the worst that humanity could do even if it tried with current technology doesn't even come close to being so fantastically destructive. We could, tomorrow, start polluting the earth to the absolute straining maximum of our ability and follow this up with the launch of all our nuclear weapons everywhere in the world, and we'd kill ourselves off (or at least enough of us to no longer be able to continue our destruction efforts in a meaningful way) long before we'd more than pull off a tiny fraction of the destruction one large asteroid causes.
And no, we wouldn't at all ruin the Earth's ability to sustain life. Our planet and its ability to regenerate ecosystems has survived multiple impacts my massive asteroids, at least a couple of impacts by literal small planets, at least two total ice ages in which the planet turned into an essential snowball (think ice caps from pole to pole) and at least three massive magmatic events (that I can think of off the top of my head) spanning whole subcontinents worth of lava flow and multiple massive volcanoes erupting constantly, without pause, for hundreds of thousands of years, only for life to bounce back from all of this.
It's pure ignorant hubris to think that any human effort today could come close.
I agree that, obviously, large scale asteroid impacts and other major cataclysms have exponentially bigger immediate destructive outcomes. Ridiculously so.
That doesn't mean the atmosphere itself, and the weather systems governing them, don't have to be kept in balance from the inside. It's a different kind of threat, man-made effects on the planet, sustained and over time. Two different systems – one where the life-sustaining systems suffer an acute disruption but then can naturally restore itself over time, and another where the nature of the system itself could slowly be adjusted, potentially compromising its basic life-sustaining qualities.
I wouldn't say it's a bigger threat than large asteroid impacts or cataclysmic events – though, those are relatively minuscule percentages, where the other is something approaching 100% on our current trajectory –, but that doesn't mean it can be dismissed as a threat in itself to the planet's life-sustaining properties. Every threat merits attention, regardless of how they compare.
And the threat is not about human effort, it's about ignorant human hubris.
You should really look deeper into the effects of large historical asteroid impacts and other major cataclysms. Literally, the worst that humanity could do even if it tried with current technology doesn't even come close to being so fantastically destructive. We could, tomorrow, start polluting the earth to the absolute straining maximum of our ability and follow this up with the launch of all our nuclear weapons everywhere in the world, and we'd kill ourselves off (or at least enough of us to no longer be able to continue our destruction efforts in a meaningful way) long before we'd more than pull off a tiny fraction of the destruction one large asteroid causes.
And no, we wouldn't at all ruin the Earth's ability to sustain life. Our planet and its ability to regenerate ecosystems has survived multiple impacts my massive asteroids, at least a couple of impacts by literal small planets, at least two total ice ages in which the planet turned into an essential snowball (think ice caps from pole to pole) and at least three massive magmatic events (that I can think of off the top of my head) spanning whole subcontinents worth of lava flow and multiple massive volcanoes erupting constantly, without pause, for hundreds of thousands of years, only for life to bounce back from all of this.
It's pure ignorant hubris to think that any human effort today could come close.