In the book Doing Good Better, William Macaskill lists a lot of great charities that are doing really good work. Consider getting a very high paid job and donating a large percent of your money to an effective environmental charity. I don't have the book on hand but I can find out the recommended environmental charities if you would like to know. He also has a careers guide on his website about how you can make the most impact: https://80000hours.org/career-quiz/
On a more personal level, eating vegan, only ever taking public transport, buying second hand, limiting consumerism, reducing packaging consumption, and adopting rather than having your own child are great steps that can be taken too.
The linked article about a potential 12C hothouse earth is a real cheery read: https://www.wunderground.com/cat6/Losing-Marine-Stratocumulus-Clouds-Could-Create-Mega-Hothouse-Climate
Are you proposing air capture? Dialysis of carbonate from seawater, where it is in equilibrium with atmospheric CO2, is much more efficient. Sequestration as composite structural lumber to displace wood timber is the most economical, but it won't be profitable until around 2024.
Read Hansen's book. He spends several chapters going through the main evidence for climate change and it's all simple physics and geological history.
It's not based on anything, except that it's lower than worse extinctions and higher than minimal events. The main point is that it's not Permian-level.
> I did a quick search for the percent of all orders that went extinct as a result of the Permian–Triassic extinction event and didn't find any estimates.
Really? I've definitely seen numbers for that, broken down by sea-life and land-life. But you might be better off with a book. I've read Erwin's "Extinction: How Life on Earth Nearly Ended 250 Million Years Ago", but you might find something more recent.
Do you have a paleoclimatology background? Richard Alley's 2 mile time machine is good for scientists / general public I would say.