the Danube is a river

Because you have the wrong information.

Climate change is provoking climate instabilities. Yes, the sea will rise, and it will affect some estuaries, but not enough to go far inland. However, the instabilities also mean less rain in some places, and flooding in others. It makes the climate less stable.

So, climate change will make some places become dry and unable to grow food. Maybe not year round, but if a crop is planted in the spring, and the summers now have a few scorching heat waves every year, it will make them fail.

The Danube is a river that runs from the south of Germany to the Black Sea.

As temperatures rise and snowpack in the Alps is depleted, the volume of water flowing into the Danube falls over time.

The Atlantic Ocean is rising with melting polar ice. The rivers of Central Europe don't have access to that glacial run-off.