Sunlight is the source of energy for the Earth's oceans, atmosphere, land, and biosphere.
Averaged over an entire year and the entire Earth, the sun deposits 342 Watts of energy into every square meter of the Earth. Most of the sun's heat is deposited into the tropics of the Earth. This is because the Earth's rotational axis is almost perpendicular to the plane of Earth's orbit around the sun. The polar latitudes receive on average much less solar heating than the equator. Climate in January would be the same as climate in April or July, all over the Earth.