Physical Environment- Global Climate

MAIN LEARNING GOALS:
* Distinguish between weather and climate, and understand how each are important ecologically
* Understand the factors that determine the global patterns of temperature, winds, and precipitation

Physical environment is the ultimate control on where organisms can live, and the resources available to support them
- includes climate, soils, water and air chemistry

Climate is the most fundamental characteristic of the physical environment- includes temperature, humidity, precipitation, wind

Weather is the current condition
Climate is the long-term averages and variation in weather; it is the expected weather for a given location, based on long-term conditions
Climate includes the variation in daily, seasonal, and long-term (e.g. El Niño) weather

Extremes in weather, outside of the normal climatic variation are important ecological forces

Global Energy Balance Drives the Climate System

Gain in energy – loss in energy (net energy balance) determines changes in temperature

Gains for the atmosphere and Earth come from:
* solar radiation
* reradiation of energy emitted from the surface by “greenhouse gases” (CO2, H2O, N2O and others)

Losses occur through:
* reflection (atmosphere, clouds, and surface),
* radiation
* conduction (transfer through direct contact) and convection (transfer by moving wind and water) (sum = sensible heat),
* and evaporation of water

Differences in the amount of solar radiation received across the surface of Earth drive global wind and water circulation

Greatest amount of solar radiation is received between 23.5° N and S latitude (= tropics)

Least radiation occurs above 67.5 °C N and S
Sun’s rays are spread out over a greater area at high latitude, and must travel through more atmosphere

Greater heating in the tropics results in storm formation
Warm air pockets form, which rise due to lower density compared with surrounding air; As the air rises, it expands due to the lower pressure (density) of air at higher altitude; The expanding air cools, lowering its ability to hold water in vapor form; clouds form, leading to convective cells (thunderstorms)

Differential heating at the global scale leads to the development of large-scale wind circulation cells

Circulation cells determine climatic patterns & biomes
Polar cells formed by cold air subsidence (descending) (Polar Climatic Zone)
Mid latitude cells (Ferrell cells) associated with transfer of energy between poles and tropics (Temperate Climatic Zone)
Hadley Cells associated with Tropical Climatic Zone

Circulation cells and Coriolis effect determine prevailing surface winds
Coriolis effect- apparent force due to the rotation of the Earth; wind and water appear to be deflected clockwise in N hemisphere, counter-clockwise in S hemisphere
Ocean currents are driven by surface winds
Zones of upwelling occur along some shorelines of the continents; Deeper water is rich in nutrients, enhancing growth of marine algae in zones of upwelling

Ocean currents transfer around 40% of the total energy exchanged between the tropics and the poles

Atmospheric circulation cells and ocean currents determine global patterns of temperature and precipitation

Seasonal variation in temperature; extreme temperatures are important to distribution and function of organisms