I support a number of charities that take on specific tasks and complete them. In fact there are charities without number who set out to do specific things. Save a specific habitat, reinstate a specific habitat. RSPB, National Trust, the various Naturalists Trust scattered around the country. Oxfam, Practical Action, if you want international ones.
It seems to me you are looking for the impossible, You want a charity with a project now that you can have 100% certainity will achieve its aims, in the future, near or far.
We simply do not know what will happen tomorrow, let alone a year, 2 years, 10 years or a century for now, so certainity is impossible. All you can do is look at charities as they are now. make a judgement on what knowledge is available now and may be your money will be well spent with long term effects, or you could put in a project that 5 years from now is destroyed totally by a war, a devastating flood (Nepal) or a drought and famine.
Good luck.