The greenhouse effect is a natural process that has happened for millions of years.
Sunlight shines through the atmosphere and is absorbed by the Earth's surface.
The Earth then releases infra-red or heat energy back into the atmosphere. This trapped energy is released back to the Earth's surface, keeping the planet warmer than it would otherwise be. The greenhouse effect is an important natural process. It currently keeps the Earth's average temperature at 15 C and allows life to flourish. But rapidly increasing greenhouse gas levels, caused by human activity, are changing this natural process and causing further warming of the Earth.