Aside from the fact that it's built on a bug-prone foundation (Ethereum), the idea at least gives me some hope that cryptocurrencies don't have to have a negative impact.
As for Ethereum, so far the bugs in the underlying platform have been minor; right now they're dealing with DoS attacks resulting from mispriced opcodes but that's getting fixed. Most issues have been due to poorly-written smart contracts rather than the platform. That's not entirely the fault of the contract authors; it's taking some time to figure out the attacks and best practices.
I'm not planning to launch in the near future anyway, because Ethereum is going through some major changes next year for scalability, and contracts will need to be coded differently to take advantage of that. In the meantime I've gotten a job doing Ethereum app work, so I should be reasonably well-prepared to get the technical side of things right.
I think the bigger challenge is making sure the climate action is actually effective. Something I learned from people at the MIT conference is that while carbon offsets are readily available in the voluntary market, even the certified offsets are often very poor quality, or even outright scams.
Also I'd like to figure out a governance system that doesn't rely on central administration, but that may not be workable; a more democratic system could end up funding charismatic projects that don't actually do much good. I've got some ideas though.
Aside from the fact that it's built on a bug-prone foundation (Ethereum), the idea at least gives me some hope that cryptocurrencies don't have to have a negative impact.