Enviropedia
Climate Change
Global Warming
Ozone
Air Pollution
Weather & Climate
Sustainability
Kids
INFORMATION
Climate System
Climate Change
Empirical Study
Climate Models
Palaeoclimates
Global Warming
Introduction
Greenhouse Effect
Enhanced G-Effect
Greenhouse Gases
 - Carbon Dioxide
   - Sources
   - Sinks
   - Carbon Cycle
   - Concentrations
   - Equilibrium
 - Methane
   - Sources
   - Sinks
   - Concentrations
 - Nitrous Oxide
   - Sources
   - Sinks
   - Concentrations
 - Halocarbons
   - Sources
   - Sinks
   - Concentrations
 - Ozone
 - Other Trace Gases
 - Adjustment Time
 - Summary
Greenhouse Forcing
 - Forcing Factors
 - GWPs
 - ΔF-ΔC Relationships
 - 1765 to 1990
 - Ozone
Aerosols
 - Aerosols
 - Radiative Forcing
   - Direct
   - Indirect
 - Total Forcing
Climate Variations
 - Surface Temperature
 - Precipitation
 - Other Variations
   - Stratosphere
   - Cryosphere
   - Circulation
   - Cloudiness
Detection
 - Modelling
 - Attribution
   - Latitudes
   - Stratosphere
   - Precipitation
   - Sea Level Rise
   - Fingerprints
 - When?
Future Climate
 - GCM Simulations
 - Feedbacks
   - Water Vapour
   - Clouds
   - Ice Albedo
   - Greenhouse Gases
 - 21st Century
Impacts
 - Agriculture
 - Forestry
 - Ecosystems
 - Water Resources
 - Oceans & Coasts
 - Humans & Health
Responses
 - Stabilising
 - FCCC
 - Kyoto Protocol
 - UK Programme
   - Energy Demand
   - Energy Supply
 - Evaluation
Conclusion
LINKS
Navigate

1.2.5. Horizontal Energy Transfers

Figure 1.3 illustrates how the energy transfers of the Earth-atmosphere system are in equilibrium. On a global scale and over a time period of several days and more this assumption is valid, and is adequate for an understanding of the causes of climate change covered in chapter 2. However, the real world is more complex than this.

If energy fluxes are calculated for different areas around the globe, one finds that between about 40�N and 35�S the incoming solar radiation is greater than the outgoing terrestrial radiation. Elsewhere (i.e. nearer the poles), there is a net radiation deficit, that is, more radiation is lost than received (Trewartha & Horn, 1980; Figure 1.4).

To restore equilibrium to this balance a meridional interchange of heat exists from the tropics to the poles (Figure 1.5). If this energy transfer did not occur, the equator would be 14�C warmer on average than now, whilst the North Pole would be 25�C colder (Barry & Chorley, 1992). This latitudinal transfer of energy occurs in several ways, involving the movement of sensible heat (convection processes caused by heating, rising and dispersion of surface air), latent heat (evapotranspiration processes involving evaporation of water vapour from the oceans and transpiration from land plants) and ocean currents (section 1.3).

As well as this movement of heat energy, there are other transfers which occur and must be balanced according to thermodynamic and physical principles. These include the transfer and balance of mass, momentum and moisture. The movement of heat involves the movement of air (sensible heatTransfer of energy occurs in several ways: radiation, reflection, transmission and convection-advection. Most of the preceding discussion dealt with the radiation of energy (in the form of electro-magnetic waves) from both the Sun and the Earth. Energy may also be transferred by the movement of the agent which contains it. Air heated may rise (convection), owing to its lower density than cooler air, and disperse laterally (advection). Convection-advection of air transfers energy, this energy being called sensible heat. Oceans similarly transfer sensible heat.), and moisture or water vapour (evapotranspiration). If a packet of air moves from the equator to the poles, this air must be replaced by colder air returning from the poles, having released its heat. In other words, the fluxes of air masses at specific locations around the Earth must be in equilibrium. By similar reasoning, both moisture and momentum fluxes must balance (Cubasch & Cess, 1990).

This picture is further complicated by the rotation of the Earth, which introduces a Coriolis Force on the moving atmosphere, and the axial tilt of the Earth, which affects the seasonal and latitudinal distribution of solar radiation. However, these phenomena are more usually covered in the study of meteorology, which is beyond the scope of this guide. Barry & Chorley (1992) provide a more detailed discussion for those interested. Figure 1.6 schematises a rudimentary Earth atmospheric circulation.