The energy that affects the climate on the Earth originates from the Sun.
The energy emitted by the Sun passes through space, until it hits the Earth’s atmosphere.
Only about 40% of the solar energy hitting the top of the atmosphere passes through to the Earth’s surface.
The rest is reflected, or absorbed by the atmosphere.
Here are some of the many factors that can cause the Earth's climate to get hotter or colder.
These factors are sometimes referred to as 'forcings'.
Strength of the sun
The energy output of the sun is not constant, it varies over time.
Recently it has been reducing slightly.
The next two factors are astronomical cycles.
Changes in the Earth’s orbit
The Earth’s orbit around the Sun is an ellipse, not a circle, but the ellipse changes shape.
Sometimes it is almost circular - and the Earth stays approximately the same distance from the Sun as it orbits.
At other times the ellipse is more stretched, so that the Earth moves closer and further away from the sun as it orbits.
When the Earth is closer to the sun our climate is warmer.