Perhaps the banks could assign an upward sloping bias to “high carbon” loans where a few basis points of “climate mitigation cost” are added to the rate offered across the full portfolio (and increased by a set amount in each subsequent period) and any funds generated are used to “buy down” the cost of “low/no carbon” loans. Assuming many dirty loans (across the portfolio to start with) and few no carbon loans initially, even a small “climate finance fee” could significantly impact (i.e. reduce) the rate charged for low/no carbon loans. As the loan portfolio tilts toward a higher proportion of lower carbon loans the effect would “feather” out.

At worst, you end up with a portfolio of loans that funds less carbon emissions than without the climate finance fee.

If governments, businesses or someone (anyone!) else were acting on the scale necessary to fix this climate crisis I would agree with Mark Carney. But to quote the famous war-criminal Donald Rumsfeld “you go to war with the army you have, not the one you wish you had”.