The Sun may influence the Earth's climate in several different ways which can be categorized as follows:
Variations in total energy output
Variations in the UV and EUV emission
Variations in the solar wind and magnetic field
The Sun is naturally the primary driver and energy source for atmospheric and ocean systems and the Earth's surface climate. The variations in the total irradiance over a solar cycle is only 0.1%, a number that is often used to argue that the Sun cannot explain the recent global warming. However, one should point out that it is the long term variations in the solar irradiance that is important. The latter number is estimated to have increased by 0.25-0.6% during the last 200 years.
Short Term Temperature Changes Medium Term Temperature Changes
Medium-Long Term Temperature Changes
Long Term Temperature Changes
Another Ice Age in less than 10,000yrs?
... see work by John Butler and his students