Climate: Biogeography Series (Part 5)

Part 5, in which we discuss the effects of the climate.

Geographic ranges of organisms are continually changing, shifting, expanding, and contracting with the passage of time. Most species are limited in at least part of their geographic range by abiotic factors, such as physiography and climate. All species experience specific limits in their tolerance of physical facts which directly affects their survival and reproductive success. These abiotic environmental components interact to produce a dynamic physical interaction.

Let us begin by discussing the components of climate. Climate is defined as the prevailing interactions of temperature, precipitation, wind, and light. Climate is not to be confused with weather, which is the short term interaction of these factors. Each of these factors except light is influenced by one or more of the other factors, and they are all subject to some other physical determinate such as pressure, physiography, latitude, and ocean currents.

The temperature range of a geographic region greatly restricts the type of biota found in those regions. Temperature is largely dependent on light availability, precipitation, and wind. High intensity of sun light often depicts an increase in temperature. Sun light affects the rate of evaporation of water from the earth’s surface, and it is this evaporation that produces the clouds in the sky when cooled at higher altitudes. Some clouds produce precipitation. Precipitation is a key constituent to temperature ranges, and the relationship goes both ways with high degrees of variability. Most directly, temperature affects the type of precipitation that falls to the earth: lower temperatures will freeze liquid rain and can cause snow, sleet, or hail. In very cold weather the atmosphere cannot hold much moisture, and so precipitation amounts, in terms of liquid water, are expected to be higher in warmer regions or seasons (physical factors are also inherent in time and space). Rain in the summer will lower the temperature while a period of decreased precipitation or drought often accompanies longstanding heat. Precipitation is important to the distribution of organisms because water is so precious to life. Areas of heavy rainfall, such as tropical rainforests, experience a tremendous amount of biodiversity. The organisms found in these rainforest greatly differ from those in areas of little rainfall, such as dry deserts.

The presence of wind influences the climate in numerous ways. Wind causes erosion, and prevailing winds can change the temperature. However, wind does not really affect temperature in terms of energy; rather, wind currents push warm or cool air in the direction of the currents. The air that the wind brings is either warmer or color than the air where the wind is headed. They can also push storms in the direction of these currents.

Wind patterns can be affected by a change in temperature. If wind can be thought of as the motion of air particles as well as a way for the atmosphere to juggle excess heat, and temperature as the average kinetic energy of a sample of air particles, then a change in temperature can be seen as a change in kinetic energy of the movement of air, or how fast the wind is moving. An increase in temperature will cause the air to move faster, and, with enough atmospheric moisture, can cause the raging winds characteristic of hurricanes.

Temperature, precipitation, wind, and light form a complex web of interaction, and all of these characteristics of climate are immediately affected by the latitude associated with each geographic region. Latitude is the measurement of the distance between some location and the equator. A region is generally colder the higher it sits in latitude, and warmer the lower in latitude, or closer to the equator. Because heat is not distributed evenly over the earth, there is a constant tendency to the movement of air from areas of low latitude to the poles, and for this movement to be compensated by that air from high latitudes to the equator. Latitude also affects how much sun light is available to an area. The higher the latitude of a location (the further it is from the equator), the less sun light it will receive.

There is much variability in the types of biomes found in each climate, owing to the tendency of the influential factors associated with climate. Further, temperature, precipitation, and wind are also intertwined with physiography and the currents of the oceans. Physiography describes the shape of continental Earth. The shape of landmasses has a great influence on the temperature of an environment. For example, high altitudes are colder than lower ones. This is due primarily to the thinner air found at high altitudes, which absorbs less heat directly from the sun and is less effective in retaining reradiated heat from the earth. Precipitation and wind affect the physical shape of the earth. Precipitation frequency and intensity influence surface runoff, evaporation, and soil condition. Wind causes erosion and contributes to the destruction caused by violent storms.

Ocean currents are caused by several forces including solar heating and winds. Solar heat causes the water to expand, and the water near the equator is actually about 8 cm higher than in the middle latitudes. Wind blowing on the ocean’s surface pushes the water. Water will begin to form a mound where the wind is blowing, and gravity will take over and pull the water downward, against the pressure gradient. The Coriolis Effect intervenes and, in the northern hemisphere, causes the water to move to the right around the mound of water (called a gyre). The Coriolis Effect is caused by the rotation of the earth and the inertia of the water. Also, in the case of cold ocean currents, there is less evaporation and the rising air is less moist. This makes it less likely for precipitation to occur.

Pressure is the final major constituent of environmental climate. Inequalities of atmospheric pressure invoke atmospheric movement. Put another way, air movement or wind is an attempt to equalize the pressure differential. Low pressure occurs when air is rising. When air flows from an area of high pressure to an area of low pressure, it produces wind. The rising air will also become less dense, therefore cooling. Cool air can sustain less gaseous moisture and is forced to condense as droplets of water. If the air continues to rise, pressure will continue to drop and larger droplets will be formed. Eventually, thanks again to gravity, the droplets fall to Earth in some form of precipitation.


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