What is Earth System Science?
In the phrase "Earth system science (ESS)," the key term is "system." A system is a collection of interdependent parts enclosed within a defined boundary. Within the boundary of the earth is a collection of four interdependent parts called "spheres." Earth's spheres include:

the lithosphere, which contains all of the cold, hard, solid rock of the planet's crust (surface), the hot semi-solid rock that lies underneath the crust, the hot liquid rock near the center of the planet, and the solid iron core (center) of the planet

the hydrosphere, which contains all of the planet's solid, liquid, and gaseous water,

the biosphere, which contains all of the planet's living organisms, and

the atmosphere, which contains all of the planet's air.

These spheres are closely connected. For example, many birds (biosphere) fly through the air (atmosphere), while water (hydrosphere) often flows through the soil (lithosphere). In fact, the spheres are so closely connected that a change in one sphere often results in a change in one or more of the other spheres. Such changes that take place within an ecosystem are referred to as events.

Events can occur naturally, such as an earthquake or a hurricane, or they can be caused by humans, such as an oil spill or air pollution. An event can cause changes to occur in one or more of the spheres, and/or an event can be the effect of changes in one or more of Earth's four spheres. This two-way cause and effect relationship between an event and a sphere is called an interaction. Interactions also occur among the spheres; for example, a change in the atmosphere can cause a change in the hydrosphere, and vice versa.

Interactions that occur as the result of events such as floods and forest fires impact only a local region, meaning the flood waters can only travel so many miles from the original stream, and only the trees that lie within the area on fire will be burned. On the other hand, the effects of events such as El Nino or ozone depletion may cause interactions that can be observed worldwide. For example, the El Nino event--a change in the ocean currents off the coast of Peru-- can cause changes in weather patterns all the way across North America, while ozone depletion above Antarctica may result in increased levels of ultra-violet B radiation around the world. Understanding the interactions among the earth's spheres and the events that occur within the ecosystem allows people to predict the outcomes of events. Being able to predict outcomes is useful when, for example, developers wish to know the environmental effects of a project such as building an airport before they begin construction.

Understanding the interactions that occur in the earth system also helps people to prepare for the effects of natural disasters such as volcanic eruptions; this understanding allows people to predict things like how far and in what direction the lava will flow. This relatively new field of studying the interactions between and among events and the earth's spheres is called Earth system science (ESS). There are ten possible types of interactions that could occur within the earth system. Four of these interactions are between the event and each of the earth's spheres:

event lithosphere
event hydrosphere
event biosphere
event atmosphere

The double-headed arrows () indicate that the cause and effect relationships of these interactions go in both directions; for example, "event hydrosphere" refers to the effects of the event on the hydrosphere, as well as the effects of the hydrosphere on the event. These four types of interactions can be illustrated in the Earth System Diagram below:

In addition to the above four event sphere interactions, there are six interactions that occur among the earth's spheres:

lithosphere hydrosphere
lithosphere biosphere
lithosphere atmosphere
hydrosphere biosphere
hydrosphere atmosphere
biosphere atmosphere

Again, the double-headed arrows () indicate that the cause and effect relationships of the interactions go in both directions; for example, "lithosphere hydrosphere" refers to the effects of the lithosphere on the hydrosphere, as well as the effects of the hydrosphere on the lithosphere.

These six types of interactions can be illustrated in gray in the Earth System Diagram below (note the four event sphere interactions are also included in this diagram, they are depicted in gold):

The ten types of interactions that can occur within the earth system often occur as a series of chain reactions. This means one interaction leads to another interaction, which leads to yet another interaction--it is a ripple effect through the earth's spheres. For example, a forest fire may destroy all the plants in an area (event biosphere). The absence of plants could lead to an increase in erosion--washing away--of soil (biosphere lithosphere). Increased amounts of soil entering streams can lead to increased turbidity, or muddiness, of the water (lithosphere hydrosphere). Increased turbidity of stream water can have negative impacts on the plants and animals that live in it (hydrosphere biosphere).

How Is Earth System Science Conducted?
Earth system science is conducted by examining each event sphere and sphere sphere interaction; this approach is referred to as an "Earth system science analysis" or an "ESS analysis." The examination of the interactions is accomplished by asking oneself the following questions:

1. How may each of the earth's four spheres (hydrosphere, atmosphere, lithosphere, and biosphere) have caused the event to occur? (The answers to this question are the sphere event impacts.)

2. What are the effects of the event on each of the earth's four spheres (hydrosphere, atmosphere, lithosphere, and biosphere)? (The answers to this question are the event sphere impacts.)

Note: When you do an ESS analysis, you will list the answers to Questions 1 and 2 together under event sphere interactions.

3. What are the effects of changes in one of earth's four spheres (hydrosphere, atmosphere, lithosphere, or biosphere) on each of the other spheres (hydrosphere, atmosphere, lithosphere, or biosphere)? (The answers to this question are the sphere sphere interactions.)

This approach of answering the questions above is performed during every ESS analysis; simply replace the term "event" with the event you wish to investigate.

An Example of an Earth System Science Analysis.
An ESS analysis was performed on the forest fires event that occurred in Yellowstone National Park, Wyoming. This forest fires event occurred in 1988 and destroyed tremendous areas of the park.

Below are some of the event sphere interactions discovered during an ESS analysis of the Yellowstone forest fires event:

Below are some of the sphere sphere interactions discovered during the ESS analysis of the Yellowstone forest fires event:

Lithosphere Hydrosphere Increased erosion of loose soil (see "Lithosphere Biosphere," below) may have led to increased sediments (i.e. soil particles) in streamwater, making the water "muddier." Lithosphere Biosphere A decrease in vegetation may have resulted in increased soil erosion because there were fewer roots to hold the soil in place. Lithosphere Atmosphere Ash particles in the air may have been carried by the wind and dropped on the ground miles away from the forest fires; the ash particles--which have a high pH--may have changed the pH of the soil. . Hydrosphere Biosphere Ash particles in the water may have clogged the gills of fish and other aquatic organisms and choked them. Hydrosphere Atmosphere There may have been more precipitation in neighboring areas because ash particles in the air may have become condensation centers upon which raindrops could form. Very dry, windy air may have drawn moisture out of the living grasses and trees through the process of evaporation. Biosphere Atmosphere Smoke in the air may have coated the lungs of animals--including people--and affected their ability to breathe.

Remember, these are NOT all the possible event sphere and sphere sphere interactions that could have occurred as a result of the Yellowstone forest fires. These are merely a few examples of what seem to be some reasonable causes and effects. There are many other possibilities.

Also keep in mind that as you list event sphere and sphere sphere interactions, it is important that you be able to explain why or how the interactions occur. For example, the above lithosphere biosphere interaction does not merely state "a decrease in vegetation may have resulted in increased erodibility of soil." It gives the reason "because there were fewer roots to hold it in place." Such explanations display your understanding of the science behind the interactions. These explanations are valuable for you and others because they make your "Why?" or "How?" thinking visible and they often lead to the discovery of additional ESS interactions.

Source: COTF