# 13.1: Background

An old adage is that the only constant in the universe is change. The bulk of the evidence available to paleoclimatologists (researchers who study past climate) indicates that this is certainly true when it comes to climate history. In general, this history alternates between cold, dry periods referred to as icehouse and much warmer, wetter periods called hothouse.

During icehouse episodes annual average global temperature falls enough that global ice (glaciers, sea ice, tundra, and ice caps) expands significantly. During hothouse episodes annual average temperature rises sufficiently that global ice becomes negligible or even disappears. One of the goals of the following activities is investigate what other changes take place during these episodes.

Another goal of the following activities is to examine what causes these episodes. Key factors that appear in Earth Viewer that you will experiment with include the following…

• Geography – The location and shape of the continents.
• $$CO_{2}$$ – The amount of carbon dioxide in the atmosphere in ppm (parts per million)
• Solar luminosity – The amount of energy received by the earth.
• Impacts – Asteroid or large meteorite collisions.