A British Establishmentarian heeds the voice of God:

...Sea level is predicted to rise by 3ft over the next
century, leading to huge areas of Bangladesh, Egypt and China being inundated.

We don't know the limits of nature - how much rain could fall for how long a period, how much more powerful and frequent hurricanes could become, for how long droughts could endure. The ultimate concern is that if runaway global warming occurred, temperatures could spiral out of control and make our planet uninhabitable.

Five times in the past 540 million years there have been mass
extinctions, in one case involving the destruction of 96% of species then living. But while these were the result of asteroid strikes or intense glaciation, this is the first time that a species has been at risk of generating its own demise...

See also, Aral Sea Disaster