The Physical Environment
Background Reading
Abiotic (non-living) factors are major determinants of what organisms live where. In this section we'll discuss major patterns in temperature and precipitation (climate) and how they are formed.
One major lesson you should take from this module is that the sun drives our global weather patterns. Energy arriving at the earth from the sun is either reflected or absorbed. Absorbed energy is then emitted by the earth, with the radiation either escaping to space or being retained in the atmosphere due to the Greenhouse Effect. For more info, see https://science.nasa.gov/ems/13_radiationbudget.
The first differences we'll note are ones that you are all aware of. Although the sun warms the earth, some parts of the earth are always warm (the tropics, between 30 N and 30 S), some parts are always cold ( the poles, >60 N or 60 S)), and some parts (the temperate latitudes between 30 and 60 N and 30 and 60 S) have seasons. For a good review of longitude and latitude, visit https://www.thoughtco.com/difference-between-latitude-and-longitude-4070791 . The differences across the surface of the earth ( spatial) and over time (temporal) are both due to the tilt of the earth.
The global imbalance in radiation leads to large-scale patterns in wind movement, which eventually drive ocean circulation patterns. These patterns are also influenced by the Coriolis Effect, which is due to the fact the earth rotates on its axis. For more info, see https://www.weather.gov/jetstream/circ and https://scijinks.gov/coriolis/ .
The Coriolis Effect leads to three major circulation patterns (cells) occurring above and below the equator (in each hemisphere). When air rises in each of the cells, we get low pressure and precipitation is common. Alternatively, when it descends we find areas of high pressure and dry conditions.
The movement of wind via these cells leads to ocean currents, which are also impacted by the Coriolis Effect. This leads to large gyres (circular movements of water) occurring in major ocean basins. The movement of water in these areas also means some land is closer to relatively warm or cold water, which influences local climate. Water can a major impact on climate because it typically has a more stable temperature throughout the year than land. This is due to hydrogen bonds in water.
Hydrogen bonds also lead to a atypical (among liquids) property of water. Water is its densest at 4 C, meaning ice floats and cold water sinks. Due to this, water moving towards these poles gradually sinks, leading to vertical movement of water that also impact global climate.
Besides these global patterns, regional modifiers of temperature and precipitation (climate) include proximity to water, topography, altitude, vegetation, and soils. Local scale variation, or what organisms ultimately experience, is dictated by all these factors in addition to features such as as aspect and behaviors.
Its important to realize climate has changed over time. This is due to regular and irregular cycles in ocean temperature (El Nino/La Nina) and the position and shape of the Earth's orbit and tilt.
These large-scale patterns in climate lead to major differences in the type of biological communities we find across the face of the earth. Biomes are one way to describe these communities in relation to the major plant forms we find at various locations.
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