The population is rapidly decreasing.

The population is coming down.

This problem is very serious.

Do you understand the seriousness of this problem?

The population of Japan is decreasing.

Can you answer this question?

The environmental issues are becoming more serious.

Environmental issues are becoming more serious day by day.

The next census will be conducted next year.

Demography is a part of social science that studies the structure, evolution, and problems of human population.