subTopic 6.1: Introduction to the Atmosphere
image from NASA
Earth is the only planet in the solar system with an atmosphere that can sustain life. The blanket of gases not only contains the air that we breathe but also protects us from the blasts of heat and radiation emanating from the sun. It warms the planet by day and cools it at night.
The SL unit is a minimum of 1 hour.
The SL unit is a minimum of 1 hour.
Guiding questions:
- How do atmospheric systems contribute to the stability of life on Earth?
- How do atmospheric processes interact with Earth's surface and oceans to regulate climate and weather patterns globally?
Understanding
structure of the atmosphere
6.1.1 The atmosphere forms the boundary between Earth and space. It is the outer limit of the biosphere and its composition and processes support life on Earth.
- Describe the composition of Earth's atmosphere
- Explain how the composition of Earth's atmosphere support life on Earth.
image from National Climate Assessment
The Earth's atmosphere is composed primarily of nitrogen and oxygen, as well as some argon. There are also several
other trace gases, meaning they occur in very small amounts.
The major constituents are oxygen (O2) and nitrogen (N2). Other components such as argon, CO2, NO, and O3 are
produced in minute quantities in natural processes. However, industrial and other technological human activities (such as automobile traffic) have begun to increase the amounts of materials such as CO2 by amounts that are beginning to make a difference in the balance of circulation and radiation absorption in the troposphere. Effects of these changes range from local atmospheric problems, like smog, to problems of much greater scale, such as global climate change.
other trace gases, meaning they occur in very small amounts.
The major constituents are oxygen (O2) and nitrogen (N2). Other components such as argon, CO2, NO, and O3 are
produced in minute quantities in natural processes. However, industrial and other technological human activities (such as automobile traffic) have begun to increase the amounts of materials such as CO2 by amounts that are beginning to make a difference in the balance of circulation and radiation absorption in the troposphere. Effects of these changes range from local atmospheric problems, like smog, to problems of much greater scale, such as global climate change.
- Nitrogen - 78% - Dilutes oxygen and prevents rapid burning at the earth's surface. Living things need it to make proteins. Nitrogen cannot be used directly from the air. The Nitrogen Cycle is nature's way of supplying the needed nitrogen for living things.
- Oxygen - 21% - Used by all living things. Essential for respiration. It is necessary for combustion or burning.
- Argon - 0.9% - Used in light bulbs.
- Carbon Dioxide - 0.03% - Plants use it to make oxygen. Acts as a blanket and prevents the escape of heat into outer space. Scientists are afraid that the burning of fossil fuels such as coal and oil are adding more carbon dioxide to the atmosphere.
- Water Vapor - 0.0 to 4.0% - Essential for life processes. Also prevents heat loss from the earth.
- Trace gases - gases found only in very small amounts. They include neon, helium, krypton, and xenon.
image from NASA Earth Observatory
The atmosphere consists of five layers: the troposphere, the stratosphere, the mesosphere, the thermosphere, and the
exosphere. The thickness of these layers is slightly different around the globe, and also varies according to temperature
and season.
The troposphere and the stratosphere are the
most affected by anthropogenic (or man-made) pollutants.
exosphere. The thickness of these layers is slightly different around the globe, and also varies according to temperature
and season.
The troposphere and the stratosphere are the
most affected by anthropogenic (or man-made) pollutants.
6.1.2 Differential heating of the atmosphere creates the tricellular model of atmospheric circulation that redistributes the heat from the equator to the poles.
- Explain the relationship between Earth’s energy budget and differential heating
- Using the tricellular model, describe how heat is redistributed from the equator to the poles
Earth's Energy Budget
The Earth’s energy budget refers to the balance between the energy Earth receives from the Sun and the energy it radiates back into space. Solar energy is unevenly distributed due to Earth's spherical shape, with the equator receiving more direct sunlight than the poles.
The Earth’s energy budget refers to the balance between the energy Earth receives from the Sun and the energy it radiates back into space. Solar energy is unevenly distributed due to Earth's spherical shape, with the equator receiving more direct sunlight than the poles.
https://www.nasa.gov/centers-and-facilities/langley/what-is-earths-energy-budget-five-questions-with-a-guy-who-knows/
At the equator, solar radiation is more intense, while at the poles, the sunlight strikes at a lower angle, spreading the energy over a larger area. This creates differential heating—a key driver of global atmospheric and oceanic circulation. The atmosphere and oceans work together to redistribute this energy, ensuring that no part of Earth becomes too hot or too cold.
Atmosphere as a System
James Lovelock, author of Gaia, proposes that the atmosphere owes its current composition to feedback from living systems. He remarks that life on Earth requires a particular atmospheric composition, and this composition is in turn maintained by the interaction between biological systems and the atmospheric system.
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Inputs
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Outputs
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Atmospheric Circulation and the Tricellular Model
To redistribute the heat, the atmosphere relies on the tricellular model, which consists of three major circulation cells in each hemisphere:
Together, these cells work to distribute heat from the equator to the poles, reducing extreme temperature differences across latitudes and contributing to global climate patterns.
To redistribute the heat, the atmosphere relies on the tricellular model, which consists of three major circulation cells in each hemisphere:
- Hadley Cell (near the equator): Warm air rises at the equator, creating a low-pressure zone. As this air cools, it descends around 30° latitude, forming a high-pressure zone, and flows back towards the equator at the surface. This circulation helps move heat away from the equator.
- Ferrel Cell (mid-latitudes): This cell operates between the Hadley and Polar cells. Air flows poleward and eastward near the surface and equatorward and westward at higher altitudes. It acts as a bridge, transferring heat between the equatorial and polar regions.
- Polar Cell (near the poles): Cold air sinks at the poles and moves toward lower latitudes, while warmer air rises in regions of lower pressure near the Ferrel cell. This helps regulate the extremely cold temperatures at the poles.
Together, these cells work to distribute heat from the equator to the poles, reducing extreme temperature differences across latitudes and contributing to global climate patterns.
https://revisegeo.wordpress.com/weather-climate/tri-cellular-model/
The Coriolis effect means that the atmosphere moves faster at the equator than at the poles. This leads to the prevailing winds at the surface of the air. At high altitudes in the atmosphere, air moves much faster as it moves towards the poles. This leads to the jet streams at the boundary between Hadley and Ferrel cells and the Ferrel and Polar cells.
Application of skills: Create system diagrams to represent the atmospheric system.
- label the inputs, output, stores and flows
greenhouse effect
6.1.3 GHGs and aerosols in the atmosphere absorb and re-emit some of the infrared (long-wave) radiation emitted from the Earth’s surface, preventing it from being radiated out into space. They include the greenhouse gases water vapour, carbon dioxide, methane and nitrous oxide (N2O), and black carbon (aerosol).
- List the major greenhouse gases
- Explain the role of greenhouse gases in trapping heat within Earth's atmosphere.
- Explain how greenhouse gases and aerosols influence Earth's energy balance and the greenhouse effect
Greenhouse gases (GHGs) and aerosols play a critical role in Earth's atmosphere by absorbing and re-emitting infrared radiation. This process helps trap heat within the atmosphere, preventing it from escaping into space, which in turn keeps Earth's surface warm enough to support life. This phenomenon is called the greenhouse effect.
- Explanation of CO2 Equivalent (CO2e): The CO2 equivalent measures the global warming potential (GWP) of a greenhouse gas compared to carbon dioxide over a specific time period (typically 100 years). For example, methane has a CO2e of 25, meaning that 1 ton of methane has the same warming effect as 25 tons of carbon dioxide over a 100-year period.
Carbon dioxide and water vapor are the most abundant GHGs in the atmosphere, while methane and nitrous oxide also contribute significantly to warming due to their ability to trap heat.
Although water vapor is a significant greenhouse gas, it is not included in most climate models because its concentration changes dynamically in response to global warming. Unlike other GHGs, water vapor is essential for life and cannot be mitigated.
In addition to greenhouse gases, aerosols like black carbon contribute to radiative forcing, influencing how much heat the atmosphere absorbs. While aerosols can have both warming and cooling effects, they generally contribute to the imbalance in Earth's energy budget.
Although water vapor is a significant greenhouse gas, it is not included in most climate models because its concentration changes dynamically in response to global warming. Unlike other GHGs, water vapor is essential for life and cannot be mitigated.
In addition to greenhouse gases, aerosols like black carbon contribute to radiative forcing, influencing how much heat the atmosphere absorbs. While aerosols can have both warming and cooling effects, they generally contribute to the imbalance in Earth's energy budget.
Radiative Forcing
Greenhouse gases (GHGs) and aerosols play a critical role in Earth’s climate system by influencing radiative forcing—the balance between incoming solar radiation and outgoing infrared radiation from Earth. Radiative forcing refers to the change in energy balance caused by factors that either trap heat in the atmosphere (positive radiative forcing) or reflect it back into space (negative radiative forcing).
Greenhouse gases (GHGs) and aerosols play a critical role in Earth’s climate system by influencing radiative forcing—the balance between incoming solar radiation and outgoing infrared radiation from Earth. Radiative forcing refers to the change in energy balance caused by factors that either trap heat in the atmosphere (positive radiative forcing) or reflect it back into space (negative radiative forcing).
Positive Radiative Forcing: Warming the Planet
When GHGs like carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O), and water vapor (H₂O) absorb infrared radiation emitted by Earth’s surface, they prevent the heat from escaping into space. Instead, these gases re-emit the heat back toward Earth, resulting in positive radiative forcing, which warms the atmosphere. This process, known as the greenhouse effect, is a natural and essential mechanism that keeps Earth warm enough for life to thrive.
However, human activities such as fossil fuel combustion, agriculture, and deforestation have increased the concentration of GHGs, leading to an enhanced greenhouse effect and increased radiative forcing. This is the primary driver of global warming.
Negative Radiative Forcing: Cooling Effects
Certain aerosols, such as sulfate aerosols produced from industrial emissions or volcanic activity, reflect sunlight back into space, creating negative radiative forcing. This reduces the amount of solar energy that reaches Earth’s surface, leading to a cooling effect. While some aerosols counteract the warming caused by GHGs, they do not fully offset the warming, and their effects are often short-lived in the atmosphere.
On the other hand, aerosols like black carbon (a type of soot) absorb sunlight, contributing to positive radiative forcing by warming the atmosphere directly. Additionally, when black carbon settles on snow and ice, it reduces their reflectivity (albedo), accelerating the melting process and contributing to further warming.
Radiative Forcing and Climate Change
The balance between positive and negative radiative forcing is crucial in determining Earth’s climate state. Increasing GHG concentrations cause positive radiative forcing, which raises global temperatures and triggers broader climate changes, such as:
- Melting ice caps and glaciers
- Rising sea levels
- More frequent and intense weather patterns, like storms and droughts
- Shifts in ecosystems and biodiversity
6.1.4 The greenhouse effect keeps the Earth warmer than it otherwise would be due to the broad spectrum of the Sun’s radiation reaching the Earth’s surface and infrared radiation emitted by the warmed surface then being trapped and re-radiated by GHGs.
- Define the greenhouse effect
- Explain how the greenhouse effect naturally keeps Earth warm enough to support life.
- Explain the difference between the natural greenhouse effect and the enhanced greenhouse effect
- Discuss how the enhanced greenhouse effect is linked to climate change
The Greenhouse Effect and Climate Change
The term 'Greenhouse Effect' is commonly used to describe the increase in the Earth's average temperature that has been recorded over the past 100 years. However, without the 'natural greenhouse effect', life on Earth would be very different to that seen today.
The greenhouse effect is a natural process that keeps Earth warm enough to support life. It occurs when energy from the Sun reaches Earth’s surface and is absorbed, warming the planet. The Earth’s surface then emits infrared radiation (long-wave radiation), which is partially trapped by greenhouse gases (GHGs) in the atmosphere, such as carbon dioxide, methane, and water vapor. These gases absorb and re-emit the heat, preventing it from escaping into space and keeping the Earth’s temperature stable.
Without this natural greenhouse effect, Earth would be much colder, and life as we know it would not be possible.
Role of greenhouse gases
The term 'Greenhouse Effect' is commonly used to describe the increase in the Earth's average temperature that has been recorded over the past 100 years. However, without the 'natural greenhouse effect', life on Earth would be very different to that seen today.
The greenhouse effect is a natural process that keeps Earth warm enough to support life. It occurs when energy from the Sun reaches Earth’s surface and is absorbed, warming the planet. The Earth’s surface then emits infrared radiation (long-wave radiation), which is partially trapped by greenhouse gases (GHGs) in the atmosphere, such as carbon dioxide, methane, and water vapor. These gases absorb and re-emit the heat, preventing it from escaping into space and keeping the Earth’s temperature stable.
Without this natural greenhouse effect, Earth would be much colder, and life as we know it would not be possible.
Role of greenhouse gases
- Maintain mean global temperature
- Normal and necessary condition for life on Earth
- allow short wavelengths of radiation such as visible light and UV too pass through to the Earth's surface, but they trap the longer wavelengths such as infrared radiatio
https://education.cfr.org/learn/reading/greenhouse-effect
The Enhanced Greenhouse Effect
Human activities, such as burning fossil fuels, deforestation, and industrial processes, have led to an increase in the concentration of GHGs in the atmosphere. This has caused an enhanced greenhouse effect, where more heat is trapped than is naturally balanced, leading to global warming—the steady rise in Earth’s average surface temperature.
Global Warming vs. Climate Change
While global warming refers specifically to the increase in Earth’s mean temperature due to higher GHG concentrations, climate change encompasses the broader range of changes that result from this warming. These changes include:
The increase in GHGs has disturbed the natural balance, leading to these significant environmental changes that pose challenges for life on Earth.
Human activities, such as burning fossil fuels, deforestation, and industrial processes, have led to an increase in the concentration of GHGs in the atmosphere. This has caused an enhanced greenhouse effect, where more heat is trapped than is naturally balanced, leading to global warming—the steady rise in Earth’s average surface temperature.
Global Warming vs. Climate Change
While global warming refers specifically to the increase in Earth’s mean temperature due to higher GHG concentrations, climate change encompasses the broader range of changes that result from this warming. These changes include:
- Rising sea levels
- Melting glaciers and ice caps
- More frequent and severe weather events, like hurricanes and droughts
- Shifts in ecosystems and wildlife patterns
The increase in GHGs has disturbed the natural balance, leading to these significant environmental changes that pose challenges for life on Earth.
Activity: Access the PHET Greenhouse Simulation
Using a simulation tool (or online resource), model how different concentrations of GHGs affect Earth’s temperature. Record your findings and describe how changes in GHG concentrations alter the greenhouse effect.
Using a simulation tool (or online resource), model how different concentrations of GHGs affect Earth’s temperature. Record your findings and describe how changes in GHG concentrations alter the greenhouse effect.
hl only
The HL unit is a minimum of 2 hours.
6.1.5 The atmosphere is a dynamic system, and the components and layers are the result of continuous physical and chemical processes.
- Describe how global warming is an example of a physical process within the dynamic atmosphere
- Explain the role of chemical processes in the atmosphere
The layers of the atmosphere are the result of continuous physical and chemical processes, creating a dynamic system. The layers can be defined according to height (altitude), thermal characteristics (temperature), density, chemical composition, and movement
Trophosphere:
Stratosphere
Mesosphere
Thermosphere
- Temperature declines by around 6.5°C per kilometer increase in altitude
- Wind speeds increase with altitude. The jet stream occurs at the top of the troposphere.
- Most of the atmospheric mass is found.
- Most of our weather occurs here.
- Humans and other organisms have most interaction e.g. through exchange of gases or through introduction of pollutants.
- Greenhouse gases (GHG) help to regulate the temperature of the earth.
Stratosphere
- Temperature is constant at about -60°C in the lower part of the stratosphere, which is shielded by the ozone layer but then increases with altitude.
- The air is dry.
- Winds increase with height.
- Ozone layer at the top of the stratosphere. Stratospheric ozone absorbs ultra violet radiation from the sun
Mesosphere
- Temperature declines with height
- Coldest part of the atmosphere.
- Contains strong zonal winds (east-west), atmospheric tides, planetary waves, and gravity waves.
Thermosphere
- Temperatures climb sharply in the lower thermosphere (below 200 to 300 km altitude), then level off and hold fairly steady with increasing altitude above that height.
- Solar activity strongly influences temperature in the thermosphere.
- UV and X-radiation from the sun is absorbed which breaks apart molecules into atoms (oxygen, nitrogen and helium atoms are the main components in the upper thermosphere).
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Physical Processes: Global Warming and Air Movements
Chemical Processes: Ozone Production and Atmospheric Chemistry
- Global Warming
- Global warming is a significant physical process in the atmosphere, caused by the accumulation of greenhouse gases (GHGs), like carbon dioxide (CO₂) and methane (CH₄). These gases trap heat within the atmosphere, leading to an overall increase in Earth's average temperature.
- As the atmosphere warms, changes in temperature and moisture distribution lead to shifts in weather patterns, affecting precipitation, storm frequency, and sea level rise.
- Air Movements and Atmospheric Circulation
- Air movements occur due to differences in temperature and pressure across the Earth’s surface. These movements form large-scale circulation patterns like the tricellular model (Hadley, Ferrel, and Polar cells) and smaller, localized systems like sea breezes or mountain winds.
- In areas where warm air rises (low pressure), cooler air from surrounding regions moves in to replace it, creating wind and other forms of atmospheric circulation. Conversely, cooler, denser air descends in high-pressure areas. This constant motion helps redistribute heat from the equator to the poles, regulating global temperatures and influencing local weather.
Chemical Processes: Ozone Production and Atmospheric Chemistry
- Ozone Production
- A critical chemical process in the atmosphere is the formation of ozone (O₃) from oxygen (O₂). Ozone is created in the stratosphere when ultraviolet (UV) radiation from the Sun splits oxygen molecules (O₂) into individual oxygen atoms (O). These oxygen atoms then combine with other O₂ molecules to form ozone (O₃).
- Ozone plays a vital role in absorbing harmful UV radiation, protecting life on Earth from its damaging effects. This forms the ozone layer, which is crucial for maintaining the Earth’s climate and ecosystem balance.
- Other Chemical Reactions
- The atmosphere is a site for countless chemical reactions. For example, nitrogen (N₂) and oxygen (O₂) can react under the high energy of lightning to form nitrogen oxides (NOₓ), which contribute to the formation of acid rain.
- Human activities, such as burning fossil fuels, release chemicals that alter the natural composition of the atmosphere. This includes the production of ozone-depleting substances (ODS), which thin the ozone layer, and air pollutants, like sulfur dioxide (SO₂) and carbon monoxide (CO), which degrade air quality.
Clouds and Climate Change
Clouds have a major role in reflecting some of the Sun's radiation back into space. The proportion of incident radiation reflected by a substance is called its albedo. The albedo of low thick clouds such as stratocumulus is about 90 percent. The albedo of high thin clouds such as cirrus may be as low as 10 percent. The albedo could vary with the wavelength of the radiation, but for clouds it does not as evidenced by the fact that they are white under white light. At sunrise and sunset the incident light is red, orange or yellow and the clouds reflect this light without modification. The albedo of clouds for infrared radiation is likely the same for visible light. There are two sides, top and bottom, to clouds that may be involved in the reflection of radiation.
The albedo effect has a significant impact on our climate. The lower the albedo, the more radiation from the Sun that gets absorbed by the planet, and temperatures will rise. If the albedo is higher, and the Earth is more reflective, more of the radiation is returned to space, and the planet cools.
Clouds have a major role in reflecting some of the Sun's radiation back into space. The proportion of incident radiation reflected by a substance is called its albedo. The albedo of low thick clouds such as stratocumulus is about 90 percent. The albedo of high thin clouds such as cirrus may be as low as 10 percent. The albedo could vary with the wavelength of the radiation, but for clouds it does not as evidenced by the fact that they are white under white light. At sunrise and sunset the incident light is red, orange or yellow and the clouds reflect this light without modification. The albedo of clouds for infrared radiation is likely the same for visible light. There are two sides, top and bottom, to clouds that may be involved in the reflection of radiation.
The albedo effect has a significant impact on our climate. The lower the albedo, the more radiation from the Sun that gets absorbed by the planet, and temperatures will rise. If the albedo is higher, and the Earth is more reflective, more of the radiation is returned to space, and the planet cools.
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Activity: Research how human activities contribute to the formation of pollutants like NOx and SO2. Create a diagram showing how these pollutants lead to acid rain
6.1.6 Molecules in the atmosphere are pulled towards the Earth’s surface by gravity. Because gravitational force is inversely proportional to distance, the atmosphere thins as altitude increases.
- Explain how gravitational force affects the density of the atmosphere
- Describe the standard lapse rate and explain how it affects temperature as altitude increases.
Atmospheric Pressure and Altitude:
- The Effect of Gravity:
- Gravity plays a crucial role in shaping the Earth's atmosphere. The force of gravity pulls molecules in the atmosphere toward the Earth’s surface, creating atmospheric pressure. As a result, the atmosphere is densest near the surface of the Earth, where gravity is strongest, and thins as altitude increases. This decrease in the number of air molecules with height explains why we experience lower pressure and thinner air at higher elevations, such as in mountainous regions or aboard airplanes
https://foxriverkayakingcompany.com/what-is-atmospheric-pressure/
- Gravitational Force and Altitude
- The strength of gravitational force is inversely proportional to the square of the distance from Earth's center. This means that as you move away from the surface, gravity weakens slightly, although the overall effect remains significant in the lower layers of the atmosphere. As you ascend through the atmosphere, the density of air molecules decreases, making the atmosphere less able to hold heat, resulting in cooler temperatures.
https://en.wikipedia.org/wiki/International_Standard_Atmosphere
The Standard Lapse Rate:
Temperature Decreases with Altitude
As we go higher in the atmosphere, temperature typically decreases due to the thinning of the atmosphere. This decrease in temperature with altitude is known as the standard lapse rate.
This relationship explains why mountaintops are cooler than lowland areas and why temperatures fall as you ascend in an airplane.
Temperature Decreases with Altitude
As we go higher in the atmosphere, temperature typically decreases due to the thinning of the atmosphere. This decrease in temperature with altitude is known as the standard lapse rate.
- The standard lapse rate is approximately 1°C for every 100 meters (or 6.5°C per kilometer) of altitude in the lower atmosphere, known as the troposphere.
For example:- At sea level, where air is densest, the temperature might be 20°C.
- At 1,000 meters above sea level, the temperature could drop to 13.5°C
This relationship explains why mountaintops are cooler than lowland areas and why temperatures fall as you ascend in an airplane.
Atmospheric Layers and Their Gradual Transition
Although the standard lapse rate provides a general rule for temperature change with altitude, different layers of the atmosphere (such as the troposphere, stratosphere, and mesosphere) exhibit varying temperature patterns due to differences in energy absorption and atmospheric composition.
This complex structure creates a layered atmosphere, where different forces and processes govern the behavior of gases and temperature.
Why Quantifying Pressure and Volume is Not Necessary
While it’s important to understand the relationship between altitude and atmospheric density, precise calculations of gas pressure and volume at specific altitudes are not required. The focus is on recognizing the general decrease in pressure as altitude increases and understanding that this thinning of the atmosphere contributes to the cooling effect experienced with rising altitude.
Although the standard lapse rate provides a general rule for temperature change with altitude, different layers of the atmosphere (such as the troposphere, stratosphere, and mesosphere) exhibit varying temperature patterns due to differences in energy absorption and atmospheric composition.
- Troposphere: The lowest layer, where the lapse rate is most applicable, extends to about 8-15 kilometers above Earth's surface. Here, temperature decreases steadily with altitude.
- Stratosphere: Above the troposphere, the temperature starts to increase with altitude due to the absorption of ultraviolet (UV) radiation by the ozone layer.
This complex structure creates a layered atmosphere, where different forces and processes govern the behavior of gases and temperature.
Why Quantifying Pressure and Volume is Not Necessary
While it’s important to understand the relationship between altitude and atmospheric density, precise calculations of gas pressure and volume at specific altitudes are not required. The focus is on recognizing the general decrease in pressure as altitude increases and understanding that this thinning of the atmosphere contributes to the cooling effect experienced with rising altitude.
Activity: this activity is from Center for Science Education SciEd):
- Students will collect temperature and pressure data at various altitudes.
- Watch the weather balloon launch video https://scied.ucar.edu/video/weather-balloon-launch
- Access the Student Activity Sheet and follow the instructions https://scied.ucar.edu/sites/default/files/documents/Virtual-Ballooning_Student-Activity-Sheet.pdf
6.1.7 Milankovitch cycles affect how much solar radiation reaches the Earth and lead to cycles in the Earth’s climate over tens to hundreds of thousands of years.
- Describe the three types of Milankovitch cycles
- Explain the role of the Milankovitch cycles in influencing Earth's climate over tens of thousands of years.
Milankovitch cycles describe long-term changes in Earth’s movement that affect the amount of solar radiation reaching the Earth. These cycles are responsible for the glacial and interglacial periods that have occurred over the past hundreds of thousands of years. The cycles are driven by three key factors that alter Earth’s position relative to the Sun, resulting in significant climate variations over long timescales.
The Three Types of Milankovitch Cycles
- Eccentricity (Shape of Earth’s Orbit)
- Eccentricity refers to the shape of Earth’s orbit around the Sun, which varies from nearly circular to more elliptical (oval-shaped) over a cycle of about 100,000 years.
- When Earth’s orbit is more elliptical, there is a greater variation in the distance between Earth and the Sun, leading to stronger differences in solar radiation between seasons. This affects global temperatures and contributes to the development of ice ages during periods of high eccentricity.
- Obliquity (Angle of Tilt)
- Obliquity refers to the tilt of Earth’s axis relative to its orbit around the Sun, which changes over a cycle of about 41,000 years. The angle of tilt varies between about 22.1° and 24.5°.
- A greater tilt results in more extreme seasons, with hotter summers and colder winters, while a smaller tilt leads to milder seasons. These shifts in seasonal intensity contribute to glaciation during periods of lower tilt, when summer temperatures in the Northern Hemisphere are too cool to melt the winter snow, leading to the accumulation of ice.
- Precession (Wobble of Earth's Axis)
- Precession is the wobble in Earth’s axis of rotation, which occurs over a cycle of about 26,000 years.
- This wobble alters the timing of the seasons relative to Earth’s position in its orbit. For example, precession can cause warmer summers to coincide with Earth’s closest approach to the Sun, intensifying seasonal changes and influencing the onset of interglacial periods.
https://geologyscience.com/geology-branches/historical-geology/milankovitch-cycles/
The diagram below shows how these three cycles correlate with the Earth's temperature and Ice Ages. These cycles are in the order of tens of thousands of years.
http://www.zo.utexas.edu/courses/THOC/Milankovitch_Cycles.html
Positive Feedback Loops and Climate Change
The Milankovitch cycles trigger positive feedback loops that amplify climate changes. These feedback mechanisms can either enhance cooling during glaciation or warming during interglacial periods:
Milankovitch Cycles vs. Current Global Warming
Although Milankovitch cycles have driven natural climate changes over hundreds of thousands of years, they do not explain current global warming. The rapid increase in global temperatures seen today is primarily due to human activities, such as burning fossil fuels and deforestation, which have dramatically increased GHG concentrations, particularly carbon dioxide (CO₂) and methane (CH₄).
Current warming is occurring over decades rather than millennia, indicating that it is driven by anthropogenic factors rather than the slow, natural processes associated with Milankovitch cycles.
The Milankovitch cycles trigger positive feedback loops that amplify climate changes. These feedback mechanisms can either enhance cooling during glaciation or warming during interglacial periods:
- Cooling and Glaciation: During periods of reduced solar radiation (often triggered by changes in eccentricity, obliquity, or precession), global temperatures drop. This leads to the expansion of ice sheets, which reflect more sunlight (increasing albedo), further cooling the planet. As temperatures decrease, atmospheric carbon dioxide (CO₂) levels also fall, since colder oceans absorb more CO₂, reinforcing the cooling effect.
- Warming and Interglacial Conditions: Conversely, when solar radiation increases, ice sheets melt, reducing albedo and allowing Earth’s surface to absorb more heat. The warming also causes oceans to release stored CO₂ into the atmosphere, increasing greenhouse gas concentrations, which in turn enhances the warming and helps maintain interglacial conditions.
Milankovitch Cycles vs. Current Global Warming
Although Milankovitch cycles have driven natural climate changes over hundreds of thousands of years, they do not explain current global warming. The rapid increase in global temperatures seen today is primarily due to human activities, such as burning fossil fuels and deforestation, which have dramatically increased GHG concentrations, particularly carbon dioxide (CO₂) and methane (CH₄).
Current warming is occurring over decades rather than millennia, indicating that it is driven by anthropogenic factors rather than the slow, natural processes associated with Milankovitch cycles.
6.1.8 Global warming is moving the Earth away from the glacial–interglacial cycle that has characterized the Quaternary period, toward new, hotter climatic conditions.
- Define the Quaternary period
- Explain the role of glacial–interglacial cycles in shaping Earth’s climate over the past 2.5 million years.
- Explain how global warming is pushing Earth away from the natural glacial–interglacial cycles
Earth’s climate has naturally fluctuated over geological time, with significant shifts between glacial (cold) and interglacial (warm) periods. The current geological era, known as the Quaternary period, began approximately 2.5 million years ago and has been marked by these regular cycles. However, global warming driven by human activities is pushing Earth away from the natural glacial–interglacial cycles and toward a new, warmer climate state.
https://canadiancor.com/correlates-climate-change/
The Quaternary Period and Natural Climate Variability
The Quaternary period has been characterized by alternating cycles of ice ages (glaciations) and warmer interglacial periods. These cycles are primarily influenced by Milankovitch cycles (eccentricity, obliquity, and precession), which govern the amount of solar radiation Earth receives.
During glacial periods, ice sheets expand, lowering global temperatures, while interglacial periods, such as the one we are currently in (the Holocene), see warming temperatures and ice retreat. The transitions between these periods typically occur over tens of thousands of years, allowing ecosystems and species time to adapt to changing conditions
The Quaternary Period and Natural Climate Variability
The Quaternary period has been characterized by alternating cycles of ice ages (glaciations) and warmer interglacial periods. These cycles are primarily influenced by Milankovitch cycles (eccentricity, obliquity, and precession), which govern the amount of solar radiation Earth receives.
During glacial periods, ice sheets expand, lowering global temperatures, while interglacial periods, such as the one we are currently in (the Holocene), see warming temperatures and ice retreat. The transitions between these periods typically occur over tens of thousands of years, allowing ecosystems and species time to adapt to changing conditions
.Anthropogenic Global Warming and the Anthropocene Epoch
While climate has naturally changed over the Quaternary period, the current global warming trend is unprecedented in both its speed and magnitude. Human activities, such as burning fossil fuels, deforestation, and industrialization, have dramatically increased concentrations of greenhouse gases (GHGs) like carbon dioxide (CO₂) and methane (CH₄) in the atmosphere. These GHGs trap more heat, accelerating the warming of Earth's surface.
This human-driven climate shift is now part of a new epoch referred to as the Anthropocene. The Anthropocene epoch is characterized by significant human impacts on Earth's geology, ecosystems, and climate, marking a departure from the natural cycles of the past. The rapid pace of climate change in the Anthropocene is concerning because it leaves less time for natural systems and human societies to adapt, resulting in:
A New Climatic State:
Beyond the Glacial–Interglacial Cycle
Global warming is moving the planet away from the familiar glacial–interglacial cycle toward a hotter climate that has no recent historical precedent. This shift includes:
The Quaternary glacial–interglacial cycles were predictable, with long cooling and warming phases. However, the current warming caused by anthropogenic GHG emissions is occurring at a much faster rate than any natural climate variability in the Quaternary period, raising concerns about the stability of the climate and the resilience of ecosystems and human infrastructure.
While climate has naturally changed over the Quaternary period, the current global warming trend is unprecedented in both its speed and magnitude. Human activities, such as burning fossil fuels, deforestation, and industrialization, have dramatically increased concentrations of greenhouse gases (GHGs) like carbon dioxide (CO₂) and methane (CH₄) in the atmosphere. These GHGs trap more heat, accelerating the warming of Earth's surface.
This human-driven climate shift is now part of a new epoch referred to as the Anthropocene. The Anthropocene epoch is characterized by significant human impacts on Earth's geology, ecosystems, and climate, marking a departure from the natural cycles of the past. The rapid pace of climate change in the Anthropocene is concerning because it leaves less time for natural systems and human societies to adapt, resulting in:
- Rising global temperatures
- Melting ice caps and glaciers
- Rising sea levels
- More frequent and intense extreme weather events
A New Climatic State:
Beyond the Glacial–Interglacial Cycle
Global warming is moving the planet away from the familiar glacial–interglacial cycle toward a hotter climate that has no recent historical precedent. This shift includes:
- Melting polar ice and glaciers, leading to rising sea levels
- Increasing global temperatures well beyond the typical range of interglacial periods
- Disruption of natural climate feedback loops, which could further accelerate warming
The Quaternary glacial–interglacial cycles were predictable, with long cooling and warming phases. However, the current warming caused by anthropogenic GHG emissions is occurring at a much faster rate than any natural climate variability in the Quaternary period, raising concerns about the stability of the climate and the resilience of ecosystems and human infrastructure.
Activity: Create a timeline that shows the key events in the evolution of Earth’s atmosphere, from the pre-biotic atmosphere to the present. Include major biological events that influenced atmospheric composition.
- Add visual elements like drawings, icons, or images to illustrate key moments (e.g., representation of cyanobacteria, volcanic activity, coal formation, factories emitting CO₂, etc.).
- Describe the composition of Earth’s atmosphere during each major period. How did it change?
- Analyze how biological events (like the evolution of photosynthesis) contributed to changes in the atmosphere’s composition.
- Evaluate how human activity over the last 250 years has altered the atmosphere, compared to natural changes over billions of years.
https://www.eagblog.org/news/the-evolution-of-earths-atmosphere/
6.1.9 The evolution of life on Earth changed the composition of the atmosphere, which in turn influences the evolution of life on Earth.
- Explain how photosynthesis by early life forms altered the composition of Earth's atmosphere
- Describe the role of oxygen in the formation of the ozone layer.
The evolution of life on Earth has had a profound impact on the composition of the atmosphere, and changes in the atmosphere have, in turn, influenced the evolution of life. The early atmosphere of the pre-biotic Earth was drastically different from what we experience today, but biological processes—particularly photosynthesis—played a key role in transforming it into a life-sustaining environment.
The Pre-Biotic Atmosphere
Before life evolved, Earth's atmosphere was composed primarily of:
There was little to no free oxygen (O₂) in the pre-biotic atmosphere. This early composition created a reducing environment, which was not conducive to the evolution of life as we know it today.
The Pre-Biotic Atmosphere
Before life evolved, Earth's atmosphere was composed primarily of:
- Carbon dioxide (CO₂)
- Water vapor (H₂O)
- Methane (CH₄)
- Ammonia (NH₃)
There was little to no free oxygen (O₂) in the pre-biotic atmosphere. This early composition created a reducing environment, which was not conducive to the evolution of life as we know it today.
Photosynthesis and the Oxygenation of the Atmosphere
The emergence of photosynthetic organisms, such as cyanobacteria, around 2.4 billion years ago during the Great Oxygenation Event (GOE), dramatically altered Earth's atmosphere:
- Decrease in Carbon Dioxide: Through the process of photosynthesis, early life forms used carbon dioxide (CO₂) and sunlight to produce oxygen (O₂) and organic compounds. This reduced the concentration of CO₂ in the atmosphere.
- Increase in Oxygen: As oxygen began to accumulate in the atmosphere, the percentage of free oxygen (O₂) increased significantly. This buildup of oxygen allowed for the development of aerobic (oxygen-breathing) life forms and enabled more complex organisms to evolve.
https://commondescentpodcast.com/2019/11/30/episode-75-the-great-oxidation-event/
The Formation of the Ozone Layer
One of the most important consequences of rising oxygen levels was the formation of the ozone layer in the stratosphere. As oxygen (O₂) molecules absorbed ultraviolet (UV) radiation from the Sun, they split into individual oxygen atoms. These atoms then combined with other O₂ molecules to form ozone (O₃).
The ozone layer acts as a protective shield, absorbing harmful UV radiation and making Earth's surface more hospitable to life. Without the ozone layer, life on land would have been impossible, as UV radiation can damage DNA and other essential biological molecules.
One of the most important consequences of rising oxygen levels was the formation of the ozone layer in the stratosphere. As oxygen (O₂) molecules absorbed ultraviolet (UV) radiation from the Sun, they split into individual oxygen atoms. These atoms then combined with other O₂ molecules to form ozone (O₃).
The ozone layer acts as a protective shield, absorbing harmful UV radiation and making Earth's surface more hospitable to life. Without the ozone layer, life on land would have been impossible, as UV radiation can damage DNA and other essential biological molecules.
https://ozone.meteo.be/research-themes/ozone/introduction
Atmospheric Oxygen and the Oxidation of Metals
The increasing concentration of oxygen in the atmosphere also led to the oxidation of metals in Earth's crust. For example:
Feedback Loops between Life and the Atmosphere
The evolution of life continues to shape Earth's atmosphere through feedback loops:
The increasing concentration of oxygen in the atmosphere also led to the oxidation of metals in Earth's crust. For example:
- Iron: As oxygen levels rose, iron in the Earth's oceans and crust combined with oxygen to form iron oxides (rust), which precipitated out of the oceans and created banded iron formations. These geological features provide evidence of the changes in Earth's atmospheric oxygen levels and are some of the earliest indicators of oxygenic photosynthesis.
Feedback Loops between Life and the Atmosphere
The evolution of life continues to shape Earth's atmosphere through feedback loops:
- Carbon sequestration by photosynthetic plants and algae reduces CO₂ levels, helping to moderate the greenhouse effect and global temperatures.
- Respiration by animals and the decomposition of organic matter release CO₂ back into the atmosphere, maintaining a balance in the carbon cycle.
Application of skills: Investigate the impact of albedo or different GHGs on the temperature of a closed system.
Key Terms
|
Atmosphere
Radiation Greenhouse Gases Radiative forcing Aerosols HL ONLY Longwave radiation Shortwave radiation Albedo effect Global warming potential Standard lapse rate Milankovitch cycles Stratospheric ozone Quaternary period Anthropocene epoch. |
Troposphere
Greenhouse effect Enhanced Global Warming Water vapor Methane |
Mesosphere
Nitrogen Global warming Climate change Black carbon |
Atmospheric gases
Stratosphere Troposphere Tropopause |
Classroom Material
| Subtopic 6.1 Introduction to the Atmosphere Presentation.pptx |
| Subtopic 6.1 Introduction to Atmosphere Workbook.docx |
Interactive Atmosphere Design Lab
Atmospheric Conditions activity
Composition of the Atmosphere worksheet
How Humans Changed the Atmosphere
Correct use of terminology is a key skill in ESS. It is essential to use key terms correctly when communicating your understanding, particularly in assessments. Use the quizlet flashcards or other tools such as learn, scatter, space race, speller and test to help you master the vocabulary.
Useful Resources
Atmospheric Resources
Energy in the Atmosphere
The Atmosphere
Composition of the Atmosphere - BBC Bitesize
Structure of the Atmosphere - Rice University
Atmosphere Structure - University of Wisconsin Stephens Point
Explanation of the structure of the atmosphere, with details at each level - PBS Learning
Structure of the Atmosphere Interactive - Glenco
Earth's Energy Balance
Energy in the Atmosphere
The Atmosphere
Composition of the Atmosphere - BBC Bitesize
Structure of the Atmosphere - Rice University
Atmosphere Structure - University of Wisconsin Stephens Point
Explanation of the structure of the atmosphere, with details at each level - PBS Learning
Structure of the Atmosphere Interactive - Glenco
Earth's Energy Balance
In The News:
Earth's atmosphere is slowly leaking oxygen, and scientists aren't sure why - Science Alert Sep 2016
International-mindedness:
- Impact to the atmosphere from pollutants can be localized, as evidenced by the destruction of the ozone layer over the poles of the Earth.
- Pollutants released to the atmosphere are carried by currents in the atmosphere and
TOK
- The atmosphere is a dynamic system—how should we react when we have evidence that does not fit with an existing theory?
Video Clips
Earth had a climate long before we showed up and started noticing it and it's influenced by a whole series of cycles that have been churning along for hundreds of millions of years. In most cases those cycles will continue long after we're gone. A look at the history of climate change on Earth can give us some much needed perspective on our current climate dilemma because the surprising truth is, what we're experiencing now is different than anything this planet has encountered before. So, let's take a stroll down Climate History Lane and see if we can find some answers to a question that's been bugging Hank a lot lately - just how much hot water are we in?
