If it is handled in a skillful way with careful marketing the world’s richer citizens would probably willingly pay much more for environmental management beyond their own borders than is presently the case;
the key is to convince people that they ultimately benefit and have a moral duty. There may be other sources of environmental management funding, in the form of ‘international levies’. For example, a charge could be made for communication satellites and distributed to developing countries for environmental care; all inter country gold exchanges could be subject to a charge to be distributed by the UN.