The world's pollution will be more and more serious.
或：There will be more and more pollution in the world.
There will be fewer trees in the world in 20 years.
=The world's cars will be fewer in 20 years.
There will be more people in the world in 50 years.
The world in the future will be fantastic.
The world in 100 years will be a perfect one.
There will be less clean water in the world in the future.
The world will be more beatiful in the future.
The world will be less crowded in 100 years.
