1. Destruction of life in the Ocean
Only 10% of edible fish remains in the ocean, and this number is rapidly declining.
2. Wars that could end civilisation.
A global war like World War I or II, conducted with today's vast number of nuclear weapons and new biological weapons, could end civilisation.
3. The spread of deserts.
Soil is being eroded. Deserts are spreading in areas were there used to be fertile soil and grassland.