Underwater oxygen loss threatens earth's stability, researchers warn

it wont matter how much oxygen you try to dissolve, if the temperature is too high you wont hold enough dissolved oxygen to allow aquatic life.

https://www.engineeringtoolbox.com/gases-solubility-water-d_...

Deep-sea mining has been studied and foreseen for at least 50 years, but it's never been economical. It is possible that current technology will allow for mining of nodules, but this still seems unlikely to me.

https://en.wikipedia.org/wiki/Deep_sea_mining#History

We did a reasonable job with ozone depletion, but that has much lower costs.

https://en.wikipedia.org/wiki/Ozone_depletion

The only truly global intervention I can think of whose impact might be discernible over geological timescales is the ban on testing nuclear weapons.

Nuclear weapons (so far)?

Banning CFCs perhaps?

If you want to go older and more localised you could look at forestry and fisheries laws. Sometimes we self-regulate and form a stable state, other times we over-extract until collapse

Ozone, leaded motor vehicle fuels, asbestos, acid rain, DDT, commercial whaling, atmospheric nuclear testing.

(Not all of these were existential to humans necessarily, but all have been largely successes.)

Lead in gasoline? https://ourworldindata.org/leaded-gasoline-phase-out

DNS, IP adresses and Emoji of course, all global efforts, with extinction level risks.

Ozone hole over Antarctica.

It is possible for us to work together and fix these things.

Edit:

Moving away from leaded gas might be another example.

(CFCs and leaded gas invented by the same dude, fun fact: https://en.wikipedia.org/wiki/Thomas_Midgley_Jr. Quite a legacy...)

We stopped using CFCs to fix the hole in the ozone layer

Well, we inadvertently stopped having as much children. That should help, but our current system economic systems can’t handle falling birthrates

Food?

I.E. avoiding population collapse due to lack of ecosystem carrying capacity? Eliminating famine? etc.

Historically speaking over over a billion years almost every species has consumed one thing and output another to the point of extinction while another species that consumes that grows and repeats the cycle.

Climate change has been the story of evolution since life appeared on earth and aglae filled the atmosphere with gasses.

We almost eradicated several diseases, usually screwed over by designating an Omelasan child (though, that's a bad characterization, because letting parts of the world continue to suffer and serve as a reservoir for those diseases was actually completely unnecessary).

I think that the banng of HFCs is a pretty good example of collective action.

Also, it's important to realize that climate change, as we best understand it right now, is not a "or perish" type of situation. RCP8.5 has now been soundly eliminated from the set of potential climate trajectories, so what we're left with is a question of 1) how much mass migration will be forced upon the world, with concomitant wars and social strife, and 2) how much economic loss results from that, as well as from lost opportunity by not adopting cheaper renewable energy routes.

Technological innovation has done something absolutely remarkable: the future with the cheapest and most abundant energy is the one that switches to renewable energy and storage the fastest. Every day we delay, not only do we end up with a worse climate outcome, but we also just light money on fire, with worse economic efficiency. And in economies built on the continual compounding interest of technological advancement, we subject humanity to far greater poverty for every day we delay the transition.

Most of the world will benefit from this technological change happening quickly. There will be some outliers, like the US, that choose to be poorer and less influential by actively subverting renewable energy in the marketplace (the Trump administration has done a huge amount of economic damage in only a small amount of time), but the US will come around. Texas is leading the way, because they are actually market driven more than they are politically driven, but the rest of the US is kind of screwed on that front for a while.

"We"? if by "we" you mean Chinese, then yes, as THEY have maintained a cultural structure and language far longer than we have, and adapting themselves and there environment to do that was something they have been doing successfully for millenia,China still venerates the first engineer "Gun"assigned to control the flooding on the yallu river 3300 years ago, and it is then no surprise that they are building solar, wind and other renewable fossil/carbon free energy sources at an unprecidented rate, and ultra high voltage grid systems to distribute that energy, while we wring our hands committing genocide on the Palistinians.