Much of the work of charities and NGOs goes on behind the scenes. The public facing efforts, esp. with regards environment and other indirect causes (tho also in cases such as e.g. homelessness, social welfare, human rights), are generally attempts to raise funds or, more importantly, to shore up support and public sentiment for advocacy efforts with government, industry, and other power brokers.

It is rarely, if ever, about feeling nice about yourself. In fact charity work generally demands being confronted daily with what you like least about the world. My personal experience working for an environmental NGO is that, while not entirely thankless, it is exhausting and often depressing work.

Our charity is one of the many asking individuals to take small actions in their daily lives. It's a small request and direct outcomes are difficult if not impossible to measure, however our org has been directly involved in any number of environmental policy changes across the many businesses and even cities that we work with. These efforts bubble up. From little things big things grow.

Anyone know any charities for climate change, homelessness, etc. that actually are worth donating to?

The more local the more likely it will go to measurable impacts (your local homeless shelter). If an ngo spents 10 times more in marketing compared to your donation it might be too big.

Being selfish and well intentioned are not incompatible, as long as being selfish includes the well being of those you care about and those you care about includes many people.

The many people bit is problematic due to our brain's make-up.

Which aspect of the make-up of our brains limits caring about many people?

GP is probably thinking of Dunbar's number[0] and making a distinction between caring concretely about specific individuals and caring more abstractly about the plight of many strangers. It's possible to "care" about the health and well being of arbitrary groups of people, but it really takes knowing and understanding their specific problems to make actual care effective.

[0]: https://en.wikipedia.org/wiki/Dunbar%27s_number

Dunbar's number has to do with the ability to maintain "stable social relationships", not "care". And I reject the notion that a recognition of shared humanity takes place in the abstract.

Please don't twist my words. I said nothing about the recognition of shared humanity, nor was I attempting to make any sort of deep philosophical stand. I was merely attempting to answer your specific question about the OP's viewpoint as I understood it.