Lot's of "just do this" comments in here. If its as easy as you think it is, then winning the grand prize should be pretty easy.
Do the math, grab an investor and go get $100M.
"Just plant trees." Okay do the math on how many trees you need. Figure out how your going to build a program to get that many trees planted. What incentives, partnership, funding do you need. How will it scale to the amount needed. What will the full lifecycle look like.
"Just improve soil." Okay do the math on that. What's the timeframe for return on investment. What do the logistics look like for producing soil in huge quantities and deploying it where needed. How do we then use that soil to grow plants that sequester carbon.
90% of the comments in here are just the "middle-brow dismissal" of climate change of all things. As if we can "just do X" to solve it and everyone else is an idiot.
It's a hard problem, especially because part of the problem is determining how to actually implement and incentivize the population to do it. You can't just ignore that part, or just throw up your hands "people are stupid so we're fucked." Solving the incentive problem is actually part of the problem. Any solution that ends with "people just need to learn to do/value X" is dead in the water. You can start with "people just need to learn to do/value X" but you need to end with a plan on how you will bring about that change in mentality/incentive.