2.1: Climate

Many forces influence the communities of living organisms present in different parts of the biosphere (all of the parts of Earth inhabited by life). The biosphere extends into the atmosphere (several kilometers above Earth) and into the depths of the oceans. Species distributions are limited by tolerance to abiotic conditions. Each species has a set of environmental conditions within which it can best survive and reproduce. Many different physical, abiotic (non- living) factors influence where species live, including temperature, humidity, soil chemistry, pH, salinity and oxygen levels.

For example, the tropics have very high biodiversity. Many different types of species live in the tropics with overlapping distributions. Why? Well, the answer is complex, but one of the most important factors is temperature. The warm and stable temperatures of the tropics are ideal for the metabolic process (such as growth, digestion, and development) of most organisms. Temperature is one of many abiotic forces influencing where life can exist and the types of organisms found in different parts of the biosphere. Therefore, an understanding of the physical environment is key to understanding all ecological phenomena.

So why are the tropics warm, and polar regions cold? Why are some parts of earth dry and others wet? To answer the most basic ecological question: What controls the distribution and abundance of species on Earth? We must begin with understanding Earth's climate.

Definition: Climate

Climate is the prevailing weather conditions in an area in general or over a long period (years, decades, etc.) and includes seasonal and daily changes. Descriptions of climate usually include average temperature, humidity, wind, precipitation, as well as seasonal variability. Climate is largely influenced by heat energy absorbed and transported by Earth’s atmosphere and oceans.

The ultimate source of energy driving the motion of the atmosphere and the ocean is radiant energy from the sun, which falls on different parts of the Earth in differing amounts. The oceans are the recipient of most of this solar energy, and they are therefore a major factor in regulating Earth’s climate. Water has a very high heat capacity, so it can absorb a large amount of heat without much of an increase in temperature. Water can also release large amounts of heat back to the atmosphere without its temperature declining as much as land temperatures would.

In this chapter we will examine the ways that the oceans and atmosphere interact with solar radiation to influence wind and atmospheric circulation, global ocean currents, and three distinct climate zones; the polar, temperate, and the tropical zones.

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