A few comments, which will make sense only after having looked at the links above:
Geras argues that there is no difference between the possibility of a future non-existing individual having a right, and the possibility of a future non-existing collectivity having rights. Not so if we look at it from the point of view of probability. Then the probability that there will be someone in the future is almost one; while the probability that there will be some particular individual – say my great-great-great-grandson – is much lower.
Also Geras says, of these future individuals or collectivity:
They can’t already have duties when it is impossible for them to fulfil these. How can they have rights of which they cannot yet be the beneficiaries and of which they may never come to be the beneficiaries?
But I can today have a duty that it is impossible for me to fulfil now, but that I might be able to fulfil in the future – say my duty to look after my children (I don’t have any). The same goes for rights. Couldn’t the rights and duties of these future individuals be conditional? The same way in which I have a duty to look after my children which is conditional on my having any? But does that mean that I have a duty today that I can only fulfil in the future if some set of conditions apply, or does it mean that I will have such duty in the future if the conditions do apply? The point of the conditional duty or right is exactly to escape such dichotomy. I don’t have a full-blown duty today, nor will I only have a full-blown duty in the future. I have, today, a conditional duty.
The point of conditional duties and rights is that, even if they might not be as valuable as full-blown duties, they have some moral relevance. Therefore the welfare of future generations is morally relevant, even though it might not be comparable to the welfare of an individual or collective living today. So you might not have an argument to divert funding from Africa to climate change. But you do have an argument for doing something rather than nothing.