It costs about $20 to buy the carbon offsets for a single bitcoin transaction (at least according to the first article I found on Google), so double that for the two transactions to receive and then sell. Carbon offsets in practice are often not as much as what you're paying for, so you would probably need to buy more of them to truly offset.

You would also have to factor in the pollution from e-waste generated by miners buying and replacing ASICs, although that's harder to quantify.

But we should also consider whether engaging in such a transaction is worthwhile as a matter of principle. If the organization's goals include environmentalism, does legitimizing Bitcoin by advertising their acceptance of it run counter to those goals?