People need to stop having babies
Here is a really nice article about how the population is growing out of control.
Programmes that seek actively to reduce birth rates find that three conditions must be met. First, birth control must be within the scope of conscious choice. Second, there must be real advantages to having a smaller family - if no provision is made for peoples' old age, the incentive is to have more children. Third, the means of control must be available - but also to be socially acceptable, and combined with education and emancipation of girls and women.