Yes. That's accurate. A total of 0.04% of our atmosphere is carbon dioxide. 412 parts per million (ppm). That means for every million molecules in the atmosphere, 412 are CO².
The reason this has such an impact on our planet is because, back a century and a half ago, it was at 280 ppm. And even in 2000, it was at 370 ppm. Keep in mind this is the same CO² that contributes to the entire carbon cycle, allows every plant on Earth to undergo photosynthesis, and is a significant part of our atmosphere.
Atmospheric content is important down to individual ppm. For example, some chemicals can be lethal at as low as 20ppm. One in every fifty thousand squares. Or 5% of this square.
And CO² isn't the only greenhouse gas. Similarly to carbon dioxide, methane, another very common gas, has doubled. We also used heavy amounts of chlorofluorocarbons (CFCs), which were breaking apart O³, or Ozone, in the atmosphere. They've since been banned, fortunately, but it's things like this that are hurting the environment.
Yes, it looks small, but wildlife on the planet relies on stable cycles of nutrients. Carbon, nitrogen, water, oxygen, all of them are molecules that are used heavily in biological systems, and all of them are cyclic in nature. When that cycle is disrupted and we have an overflow or drought of a certain part of the cycle, it creates an imbalance in other patterns across the planet. Climate, food webs, currents, and chemical contents change all across the planet.
That's not to say large changes over time are abnormal. But they usually happen over millions of years. Species and cycles had plenty of time to adapt and evolve to those changes. It's *rapid* change that causes significant damage to biodiversity and ecological systems. Take the KT event, for example. A giant meteor impacting the surface of the Earth is plenty enough to disrupt biological systems around the planet. And the Earth lost massive amounts of biodiversity then. Now we're doing the same thing.
It's not a matter of if life or Earth will survive. Both will. But *Humanity*'s survival is what we're worried about. That and biodiversity. And if there's a rapid change in ecological systems, it tips scales that then cause extinctions. We've known about this since we studied the KT event. It's just a matter of applying the same principles to today's changes.