If we needed to power the world on uranium fission, we could extract uranium from seawater. There is an estimated 4.5bn tonnes of uranium dissolved in seawater - if we extracted 10% of that, that would last 5,000 years at current consumption rates and without breeder reactors.
Breeder reactors can take us to millions of years, by which point, we may well have perfected other forms of energy production, population may have shrunk enough to make completely renewable energy sources more than adequate.
With nuclear, we could even contemplate actively scrubbing some CO2 from the atmosphere, converting it into oil, and pumping it underground, effectively reversing climate change. In fact, instead of sending money to poorer countries to help address future climate risk impacts, if richer countries actually put money into reversing their own contributions to climate change, that would actually be a worthwhile endeavour.