Fundamentals of Environmental Science: Systems, Models, and Earth’s Climate
Concept of Environment
The concept of environment was established in the United Nations Conference on the Human Environment. It encompasses the physical, biological, and social components that can cause direct and indirect, short- or long-term effects on human life and activities. Ecology is the science related to this concept, studying natural ecosystems, the physical environment, and living beings.
The Need for Models
A model is a simplification that mimics real-world phenomena, allowing us to understand complex situations and make predictions. It involves a simplification of reality.
Theory of Systems
A system is a set of operationally interrelated parts, where some parts act on others, and we consider the overall behavior of interest. Each system consists of elements. If a special relationship exists between two or more system elements, those elements are called a subsystem.
Examples of System Models
System models can be categorized as black box or white box models. A black box model only considers the system’s inputs and outputs. A white box model analyzes the internal contents and mechanisms of the system. Simple relationships can be direct or inverse:
- Direct: An increase or decrease in one element causes the same effect on another element (indicated by a + arrow).
- Inverse: An increase in one element leads to a decrease in another (indicated by a – arrow).
Complex Systems (Feedback)
Feedback involves actions of one element over another, which in turn affects the first element. Positive feedback means an increase in one element leads to an increase in another (and vice-versa), indicated by a (+) inside a circle. The result is exponential growth. Negative feedback occurs when an increase in one element leads to a decrease in another, indicated by a (-). It acts as a counterpoint to positive feedback, stabilizing the system and creating decreasing curves. When environmental conditions are favorable, the biotic potential of a population is high, and the population grows until limiting factors hinder growth (logistic curve). Homeostatic systems are characterized by strong interactions between the system and its changing environment. Living systems tend to remain homogeneous and maintain some independence from the exterior.
Entropy
Entropy measures the portion of unusable energy contained within a system.
The Earth as a Black Box System (Models of Regulation)
The Earth is a heat engine that combines two energy sources on its surface: solar energy and inner mantle energy. These sources are balanced to keep matter moving, distributed in outer and inner loops:
- Outer Loop: Based on the convection of fluid layers (atmosphere and hydrosphere), determining climate zones.
- Inner Loop: Based on the convection of the Earth’s solid mantle, determining tectonic plates and related phenomena.
Climate System Model
Key factors in the Earth’s climate system include: the greenhouse effect, surface ice cover, atmospheric dust, variations in Earth’s orbit, and clouds. Greenhouse gases capture infrared light (heat), maintaining an average Earth temperature of 15°C. An increase in greenhouse gases is a major environmental problem. Albedo is the percentage of sunlight reflected from Earth. It depends on the type and color of the Earth’s surface. Ice reflects more light, causing temperatures to drop and increasing ice volume. Volcanoes or meteors inject huge amounts of matter into the atmosphere, forming dust particles that reflect light, decrease surface temperature, and increase albedo. Clouds have a dual effect: they increase albedo by reflecting solar radiation, but they can also enhance the greenhouse effect by trapping infrared radiation. Other factors influencing the ice-albedo loop include:
- Eccentricity of Earth’s orbit: The Earth’s orbital path varies from circular to elliptical over 100,000 years.
- Axial tilt (Obliquity): The angle of Earth’s rotational axis varies over 41,000 years (currently at 23.27°), influencing the duration of day and night and the existence of seasons.
- Precession (Perihelion position): The position of Earth at perihelion (closest to the sun) varies every 23,000 years. Currently, Earth reaches perihelion in early January and aphelion in July.
A simple model of Earth’s climate involves a dynamic equilibrium driven by two positive feedback loops: the greenhouse effect and the albedo effect.
Comparison with Other Planets
- Venus: High surface temperatures due to a thick cloud layer that intensifies the greenhouse effect.
- Mars: Lower temperatures and lack of evolution towards a warmer climate due to a weaker greenhouse effect.
Volcanoes have a dual effect: a short-term temperature drop due to dust, and a long-term temperature increase due to SO2 and CO2 emissions, enhancing the greenhouse effect.
Environmental Change in Earth’s History
The atmosphere, hydrosphere, geosphere, and biosphere have co-evolved throughout Earth’s history.
Atmosphere
In its early stages (4.5 billion years ago), the primitive atmosphere was composed of nitrogen, CO2, water vapor, and traces of hydrogen and carbon. Around 3 billion years ago, photosynthetic organisms appeared, releasing oxygen into the atmosphere and leading to the formation of the ozone layer. Small chemical changes, such as variations in CO2 levels, can amplify during glacial periods or due to changes in vegetation.
Hydrosphere
The hydrosphere is believed to have formed about 4.5 billion years ago, initially as water vapor that condensed to form oceans. Transgressions and regressions (sea level changes) may have been caused by variations in the volume of the hydrosphere or by the uplift and subsidence of continents. Volcanic activity exerts dual effects on the climate depending on its emissions. High SO2 emissions can lead to cooling, while high CO2 emissions lead to warming. The unequal distribution of land and sea influences temperature variations. The presence of a supercontinent can promote persistent continental anticyclone conditions. Ocean currents can moderate temperatures and favor ice melting. Changes in the Earth’s axial tilt appear to coincide with periods of significant climatic changes.
Biosphere
The first living organisms are believed to have originated around 2.5 billion years ago. The first cells were anaerobic heterotrophs, obtaining energy by fermenting organic molecules. As organic molecules became scarce, some anaerobic heterotrophs evolved photosynthetic capabilities, using light to synthesize organic molecules and releasing CO2 and later O2 into the atmosphere. The use of light by photosynthetic organisms drastically changed the atmospheric composition, enriching it with O2 and leading to the formation of the ozone layer, which allowed the existence of the first aquatic organisms.