Defining Climate

Katie Muniz & Brian Bowen

Annual Averages and Variations

  • Climatology- Is the study of Earth's climate and the factors that cause past, present, and future climatic changes.
  • Climate describes the long term weather patterns of an area. These patterns include more than average weather conditions.
  • Also describes annual variations of temperature, precipitation, wind, and other weather variables.


  • Normals- the data used to describe an areas climate are compiled from meteorological records.
  • These datas include daily high and low temperatures, amounts of rainfall, wind speed and direction, humidity, and air pressure.
  • Data is averaged on a monthly or annual basis for a period of at least 30 years to determine the norm.

Limitations of normals

  • While normals offer valuable information, they must be used with caution. Weather conditions of any given day might differ widely from the norm.
  • While climate describes the average weather conditions for a region, norms apply only to the specific place where the meteorological data were collected.

Causes of Climate

  • From watching the weather reports the climates around the country vary greatly. For example, on average, daily temperatures are much warmer in Dallas, TX, than in Minneapolis, MN.
  • There are several reasons for such climate variations, including difference in latitude, topography, closeness of lakes and oceans, availability of moisture, global wind patterns, ocean currents, and air masses.


  • Tropics- The area between 23.5 degrees South and 23.5 degrees North of the equator.
  • Temperate Zones- lies between 23.5 degrees and 66.5 degrees North and South of the equator.
  • Polar Zones- Located from 66.5 degrees North and South of the equator to the poles.
  • The amount of solar radiation received by any one place varies because Earth is tilted on its axis, this affects how the sun's ray strike our surface.

Topographic Effects

  • Water heats up and cools down more slowly than land. Large bodies of water affect the climate of coastal areas.
  • Temperatures in the lower atmosphere generally decrease with altitude, mountain climates are usually cooler than those at sea level.

Air Masses

  • Two of the main causes of weather are the movement and interaction of air masses, air masses also affect climate.
  • Average weather conditions in and near regions of air mass formation are similar to those exhibited by the air masses themselves, for example consider the Island of Dominica.