I don't trust what Giving What We Can recommends for this issue. The biggest thing done recently on this issue was the IRA, and I don't think the six charities referenced here (https://www.givingwhatwecan.org/donate/organizations#addressing-climate-change) did much or anything necessary on the margins to contribute to that passing. I also don't see how many tenths or hundredths of a degree of warming $x will prevent for each org, and the majority of the orgs have something like 'We don't currently have further information about the cost-effectiveness of [this org] beyond it doing work in a high-impact cause area and taking a reasonably promising approach,' under the question 'What information does Giving What We Can have about the cost-effectiveness of [this org]?'
That seems extremely not rigorous. :p
What even makes these orgs reasonably promising compared to others? Vibes?
I looked into this a number of years ago and it doesn't seem like Founders Pledge's methodology has changed since then. You can read their Cause Area Report for more depth, but the primary metric they rate on is tonnes of CO2-equivalent pollutants averted per year per U.S. dollar (CO2-equivalent uses simple weights to compare between different greenhouse gases, such as methane). They have somewhat strong estimates per charity, such that in 2018, the Clean Air Task Force and Coalition for Rainforest Nations came out ahead—but with the proviso that this extrapolated past performance into the future, which isn't a given with lobbying organisations.
I agree that GWWC could use more depth here, and at the same time I tend to agree that they're right to recommend Founders Pledge first.