Learning Objectives

2.5.1 Explain how the tilt of Earth's axis influences (1) seasonal changes in air temperature in temperate and polar zones and (2) seasonal changes in precipitation in the tropics.

2.5.2 Outline how seasonal changes in surface heating in temperate and polar lakes influence water density and result in the stratification of water.

2.5.3 Describe how cyclic change in the position and strength of high- and low-pressure cells influences weather and climate variability.

As noted at the beginning of this chapter, understanding climate variation is critical to understanding ecological phenomena such as the distributions of organisms. Climate variation at daily to multi-decadal time scales determines the range of environmental conditions experienced by organisms as well as the availability of the resources and habitats they need to survive. Long-term climate variation over hundreds and thousands of years influences the evolutionary history of organisms and the development of ecosystems. In this section, we will review climate variation, from seasonal to decadal time scales.