Suppose you had 10 dollars that you are required to pay to mankind. How would you actually do this?

Put it into a fund that is spent on: promoting technologies and practices that harm less, inhibiting technologies and practices that harm more, repairing specific damages done [eg.: restoring fisheries destroyed by oil company spills, counter-acting coastlines being eroded away, campaigns to protect low-lying coasts from inundation (or remediating the cost of abandoning them), etc.}.

So in other words donate money to a business which promise things you think are good ideas.

You know of course, that one of the promises of the Shuttle program was to significantly lower cost to space.

And you know of course that a private company, a public company, non profit company, or an agency of a govt can promise something but not actually accomplish what they say they are going to do.

And you know of course, that their are non profit companies involved with saving children from severe conditions of poverty and violence. There are such groups as "doctors without borders" etc that do work which actually has measurable effects. Or you have such groups as obvious institutions as the Red Cross.
One thing is very obvious and without any doubt, there are a lot of organization which need a lot money donated to, but you choose an organization which is going to clean up beaches. Some might call that selfish, but most people realize that one is free to donate your money to whatever cause you think is important. But the issue in this case is you are apparently choosing something "for mankind", and therefore you could be properly called selfish, narrowminded, and basically an idiot.