1, 2, and 3 is called the Milankovitch cycle (when the "big bang" or whatever happened when the universe formed, it created a universe, including a solar system, that isn't uniform or static. things do not happen on a human time scale. orbits are not round and everything wobbles, kind of like the tires on your car - though they appear round, you need them balanced to not, well, bounce! no one balanced our solar system!)
1. eccentricity: shape of the earth's orbit around the sun oscillates on a 100,000 year cycle. any small increases in distance to the sun means a huge amount of increase in solar energy.
2. axial tilt: the earth's axis is currently tilted at an angle of 23.5 degrees, but this doesn't always stay the same. oscillations in the degree of earth's axial tilt occur on a periodicity of 41,000 years from 21.5 to 24.5 degrees. the varying amounts of sunlight around the earth during the year creates the seasons. the teetering of the earth's tilt creates more or less seasonality.
3. precession: the earth's slow wobble on its axis, much like a top that is about to fall over (not that the earth would "fall over"). the precession of earth wobbles from pointing at the north star to pointing at the star vega. this top-like wobble has a periodicity of 23,000 years and would cause greater seasonality.
4. sun cycles: just like the earth, the sun also has its own cycles. we all have heard about the flares (which is a short cycles, like every 11 years or something, clearly not associated with warming or cooling), but i'm sure that the sun wobbles, oscillates, swells, shrinks, etc. just like the rest of the universe!
5. ocean currents: the heating or cooling of the earth's surface can cause changes in ocean currents. the ocean currents play a significant role in distributing heat around the earth so changes in these currents can bring about significant changes in climate. stronger and more frequent el nino/la nina cycles are a result of warmer ocean temperatures. (el nino = cold, wet winter in the southeast US = the stronger the el nino = the colder and wetter!)
7. volcanoes: not only do volcanoes emit greenhouse gasses such as co2 and water vapor, they also create landmass that can change the circulation of the ocean. imagine our earth before costa rica and panama were formed. the atlantic and pacific oceans were connected and freely flowed westward - when that island arc was formed, the ocean currents drastically changed and i bet the climate changed too!!!
8. changes in greenhouse gasses: when global temperatures become warmer, carbon dioxide is released from the oceans. i.e., when changes in the earth's orbit trigger a warm period, increasing concentrations of carbon dioxide may amplify the warming by enhancing the greenhouse effect. when temperatures become cooler, co2 enters the ocean and contributes to additional cooling.
9. water vapor: i can't NOT talk about water vapor. water vapor is such a green house gas, people don't talk about it though. it isn't something that affects climate change on a large scale (probably) but it is a greenhouse gas.
10. did i say anything about people? no. did i say anything about burning coal, clearing land, cow farts, car emissions, CFCs, or al gore? no (well, i not until now, anyway...).