Overpopulation is caused by factors like reduced mortality rates, better healthcare, and depletion of resources. It affects world population day which aims to raise awareness of issues like family planning and sustainable development. The effects of overpopulation include depletion of natural resources, negative environmental impacts, rising unemployment, high living costs, and increased conflicts. Solutions include better education, promoting family planning awareness, tax benefits, and teaching sex education to control the population and ensure a sustainable happy life.