Probably planting trees as effectively it's free to scatter seeds you find.

Plant a fuckload of protected species trees

Put that money in stocks or ETFs that align with your climate goals. You don’t even have to dig too deep to find ones that meet your needs. Much digital ink has been spilled on the topic. Just find one or two you like and go for it.

In a general sense, put the money where you want change to happen in this version of reality.

Put it in a bank that doesn't invest your money into the wrong stuff. In fact a bank can loan more money than it has, but there's a ratio set by law. So for example that could effectively be 30k in arbitrary investments.

If you want to spend it, I'd buy a good bicycle or get my home isolated or sum like that. You could get cooking lessons and proper cookware and stay away from processed foods that generate tons of waste. If you have the space you could grow your own vegetables and have chickens, which eat bio waste. Basically reduce what you buy. You could get tools and learn how to fix things if that's more up your alley. For example I've fixed my Sennheiser headphones several times, but it did need some investment in tools. You could also donate it to a repair café.

Get a vasotomy/tubal ligation.

Start a fund raiser, do advertisement, (make some donations your self so that it does not look dead) - ones you get a lot of money (lets say you have doubled) - start again and repeat until you double - within 10 cycles of doublings, you reach 10 million, and keep doing until you get rich enough (lets say 10 more cycles to reach 10B) then you have 2 paths to choose - either be a hero and actual invest in research and actively reversing shit done, maybe helping displaced or other good deeds, or the mlm path, and continue the doubling cycle, keep earning - with this much money, you can now have actors and fake donations, maybe even fake researches into how you are helping, and keep growing your wealth, and maybe then escape to a tax heaven.

Apologies for the dystopian ending, but realistically a person even going full carbon negative is not even a dent. If you actually want to do good, then you realistically require trillions, and then you feed that money to politicians, and reverse launder your way towards actual green solutions.

Not 10k but I would figure something out with 100k

Fund a sterilization program for young people who have come to understand the future that humanity is hurtling towards, and who want to avoid bringing a child into such a brutally cruel future.

Both my niece and nephew have sworn off of children, as they have good educations and have fully understood just how badly humanity is fucking itself over. They’re just trying to find doctors that will do those procedures on people under 30.

I'd probably donate it to the Thorium guys. Either the ones that just built the reactor research lab in Texas, or the shipyard ones. If coal becomes economically obsolete, the gigatons of CO2 will drop off like a rock.

Become a shareholder for one of the many giant corporations responsible, and try to sway them into cleaning thier mess up.