Climate Basics

How Does the Climate System Work? (video)

Climate Definition

The American Meteorological Society (AMS) defines "climate" as follows:


climate

Climate is the slowly varying aspects of the atmosphere–hydrosphere–land surface system. It is typically characterized in terms of suitable averages of the climate system over periods of a month or more, taking into consideration the variability in time of these averaged quantities. Climatic classifications include the spatial variation of these time-averaged variables. Beginning with the view of local climate as little more than the annual course of long-term averages of surface temperature and precipitation, the concept of climate has broadened and evolved in recent decades in response to the increased understanding of the underlying processes that determine climate and its variability.




The term "weather" is distinct from "climate" and is defined by the AMS as follows:


weather

Weather is the state of the atmosphere, mainly with respect to its effects upon life and human activities. As distinguished from climate, weather consists of the short-term (minutes to days) variations in the atmosphere. Popularly, weather is thought of in terms of temperature, humidity, precipitation, cloudiness, visibility, and wind.

Earth/Sun Relationship

The sun is the primary source of energy that creates almost all climate conditions on Earth. The spacial relationship between the Earth and the sun determines the amount of solar radiation received by different areas of the Earth. For example, the Earth's north and south poles receive less solar radiation than do areas near the tropics, because of the orientation of the Earth to the sun.


The spacial orientation of the Earth to the sun takes a variety of forms, each of which changes over varying amounts of time. These do have some effect on the climate of the Earth, mostly over time periods of thousands or millions of years. The following are ways in which these spacial relationships manifest:

  • Earth's daily rotation
  • Annual seasonal changes as the Earth orbits around the sun
  • Earth's elliptical orbit, resulting in changes in the distance of the Earth to the sun
  • Changes in the degree of tilt of the Earth
  • Changes in the direction of tilt of the Earth


In addition to the spacial relationships between the Earth and the sun as listed above, there is also the possibility that changes in solar irradiance could have an effect on the Earth's climate.



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The Earth System

Climate is created and exists within the context of the Earth System. The Earth System is defined by the following subsystems:

  • atmosphere
  • geosphere
  • hydrosphere
  • cryosphere
  • biosphere


Within the context of the Earth/Sun relationship and the global distribution of solar radiation, the interactions between the various Earth systems determine almost entirely the climate conditions that exist across the Earth.


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Earth System Interactions

The Earth's climate is the result of interactions between its various systems - atmosphere, oceans, lithosphere, cryosphere, and biota. Following are some of the dominant system interactions.

  • Ocean surface currents
  • Deep ocean thermohaline circulations
  • El Nino Southern Oscillation (ENSO)
  • Volcanic Activity
  • Deforestation
  • Desertification
  • Cryoscopic Changes

Variables Used to Describe Climate

There are several variables that are used to describe climate at any region of the Earth. Most of those variables are as follows:

  • Atmospheric pressure and circulation
  • Temperature
  • Precipitation
  • Humidity
  • Wind
  • Latitude
  • Topography
  • Altitude
  • Atmospheric particles
  • Local features

Climate Classifications

It is important to classify different climate conditions at different parts of the Earth in a systematic way. There are numerous approaches to this process, and the most commonly used method is the Koppen-Geiger Climatic Classification System. Using codes consisting of letters assigned specific climatic properties, the Koppen-Geiger system allows a close description of climate at virtually all parts of the Earth.


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Hydrologic Cycle

The hydrologic cycle is the extent and movement of water in the various Earth systems - the atmosphere, hydrosphere, lithosphere, cryosphere and biosphere. Any description of the hydrologic cycle must include the phases of water - gas, liquid and solid ice - that exist in all the Earth systems.



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Carbon Cycle

The carbon cycle is how carbon is transferred through the various earth systems. Those systems include the atmosphere, the oceans, plants, animals, and rock formations. Since carbon is the main component of the greenhouse gases carbon dioxide and methane, a knowledge of the carbon cycle can help in understanding the effect of carbon on the present climate and how climate may change in response to varying amounts of carbon-based greenhouse gases in the earth systems.


In addition, carbon is a critically fundamental element in the tissues and other substances that form living organisms. No life, as we know it, can exist without carbon and the multifarious compounds that are possible because of it. Living organisms are key components in the absorption and release of carbon into and out of earth systems. Therefore, a study of the carbon cycle is central in understanding how life and climate are entwined.



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Paleoclimatology

Paleoclimatology is the study of the ancient history of climate. The nature of climate prior to 19th century is not available from records of direct observation and specific measurements. Therefore, climate from those times of long ago must be ascertained by data gathered indirectly from sources carrying the aftereffects of ancient climate conditions. These data are known as "proxy data".


Examples of sources for proxy data are:

  • sediments from lake beds
  • ice cores from ice sheets
  • tree rings
  • coral

Climate Models

Climate models are complex, mathematical descriptions of the variance of climate conditions. They are based on past climate data and formulas of how climate components interact. Climate models are used to explain current climate conditions and predict climate conditions in the future. These models are usually incorporated into computer programs that allow massive, complex, climate data to be processed as rapidly as possible.