Geologic climate change refers to climate change that takes place over long periods of time such as over thousands of years and longer. Also included will be factors that can change the climate almost instantly. Each of these will be discussed below:

1. Solar variability: The energy received from the sun plays a critical role to the climate. Just a 1% change in solar output will dramatically change Earth’s climate. A decrease in solar output will cool the climate dramatically while an increase in solar output will warm the climate dramatically. The sun seems like a constant nuclear furnace but the amount of energy emitted from the sun changes over long periods of time. Sun spot activity can change solar output on yearly time scales (such as the 11-year sun spot cycle) while the very slow increase of solar output occurs over millions of years from the normal lifecycle of solar output.

2. Meteor impacts: A large meteor impact will significantly cool the climate. The massive amounts of fine debris after collision with the Earth produces a cloud of dust worldwide that decreases the amount of solar radiation that can reach the surface. This global cooling dramatically alters Earth climate on very short time scales.

3. Milankovitch Cycles: The three cycles include the amount the Earth is tilted (currently 23.5 degrees), the shape of the orbit of the Earth around the sun (currently less eccentric) and the wobble of the Earth’s rotational axis (currently winter occurs when Earth is closer to the sun in the Northern Hemisphere). These factors combine to produce either a cooler climate or a warmer climate. The combination of factors also can lead to changes in seasonal variability. These cycles occur over 1000s and 10s of 1000s of years thus they have basically a negligible impact on climate change in short time frames such as during 100 years. Over thousands of years they do have a major impact and are one factor that could lead to the ice age cycles.

4. Surface properties: The percentages that the Earth is water, ice and land has a major impact on Earth’s temperature. More reflective surfaces such as ice will cool the temperature while less reflective surfaces such as water warm the temperature. The distribution of the continents is also important since this impacts global ocean currents. Ocean currents that are able to travel from pole to pole (such as it is now) helps moderate the climate. A continent near the pole (such as Antarctica) can lead to huge buildups of ice.

5. Volcanic Activity: A significant amount of volcanic activity can send large volumes of dust into the atmosphere which blocks some of the incoming solar radiation from the sun. This can lead to a global cooling. Volcanic activity will cause climate change on very short time scales.

6. Human Activity: The ability of humans to alter the land and the chemistry of the air can create climate change. The introduction of greenhouse gases in theory has a warming effect on the climate. The changes to surface cover from cutting down forests and changing vegetation types can also have an impact since it changes the albedo of the surface and the chemistry of the air.