Definding Climate


Annual Averages and Variations

  • Definition: 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 much more than average weather conditions.
  • Climate also describes annual variations of temperature, precipitation, wind, and other weather variables.


  • Definition: Normal: -- The data are averaged on a monthly or annual basis for a period of at least 30 years to determine.
  • The data used to describe an area's climate are compiled from meteorological records, which are continuously gathered at thousands of locations around the world.
  • These data include daily high and low temperatures, amounts of rainfall, wind speed and direction, humidity, and air pressure.

Limitation of Normals

  • While normals offer valuable information, they must be used with caution. Weather conditions on any given day might differ widely from normals.
  • While climate describes the average weather conditions for a region, normals apply only to the specific place where the meteorological data were collected.
  • Changes in elevation and other factors, such as proximity to large bodies of water, can cause climates to vary.

Causes of Climate

  • There are several reasons for such climatic variations, including difference in latitude, topography, closeness of lakes and oceans, availability of moisture, global wind patterns, ocean currents, and air masses.
  • For example, on average, daily temperatures are much more warmer in Dallas, Texas, than in Minneapolis, Minnesota.


  • Tropics: The area between 23.5 degrees south and 23.5 degrees north of the equator.
  • Temperate Zone: lie between 23.5 degrees and 66.5 degrees north and south of the equator.
  • Polar Zone: are located from 66.5 degrees north and south of the equator to the pole.

Topographic Effects

  • Many coastal regions are warmer in the winter and cooler in the summer than inland areas at similar latitudes.
  • Temperatures in the lower atmosphere generally decrease with altitude.
  • Air rises up one side of a mountain as a result of orographic lifting.

Air Masses

  • Two of the main causes of weather are the movement and interaction of air masses. Air masses also affect climate.
  • Recall the air masses have distinct regions of origin, caused primarily by differences in the amount of solar radiation.
  • Average weather conditions in and near regions of air-mass formation are similar to those exhibited by the air masses themselves.