Which ones we should use:
the global population
English Language Learners Stack Exchange is a question and answer site for speakers of other languages learning English. It only takes a minute to sign up.Sign up to join this community
You would usually talk about the global population
The global population is likely to exceed 9 billion within 10 years.
But in some contexts the indefinite article might also be used:
Earth's resources could not support a global population of more than 10 billion.
It would be correct to omit the article entirely when using such constructions as global population growth.
Global population growth is likely to strain earth's resources within 50 years.