The sun drives climate on the Earth, while the tilt of the Earth's axis causes the seasons. In taking a systems approach, we must look at how the atmosphere, hydrosphere, lithosphere, and biosphere all interact with climate.
Causes of climate change may therefore be many; they may originate with sun itself or from one of the -spheres. Causes external to the Earth include mostly solar causes: variation in the quantity or wavelengths of solar output, in the Earth's orbit about the sun, in the amount of dust that solar radiation encounters en route to the Earth.
Causes of climate change from the Earth itself, or intrinsic causes, include anthropogenic sources, like aerosols, carbon dioxide, or CFC's; or perhaps feedback mechanisms on the Earth (one example: a growing ice sheet will increase the Earth's albedo and reflect more energy from the Earth, making it colder and further causing the ice sheet to grow).
These and more possible causes are on the pages in the handouts. Some are possible candidates, some have been ruled out.
We got a five-page handout. Click below for the page and my notes that go along with them.