Earth's tilted axis causes the seasons. Throughout the year, different parts of Earth receive the Sun's most direct rays. So, when the North Pole tilts toward the Sun, it's summer in the Northern Hemisphere. And when the South Pole tilts toward the Sun, it's winter in the Northern Hemisphere.
The worlds population is increasing a lot, and fast. It was steady and rising lightly until the 1950's, then population really grew. Todays current world population is 7.8 billion in 2020.