Chapter 4: Complexity of the climate system.
Introduction
Why is the warming of the Earth a concern?
Watch the video and list the consequences of global warming.
optional: Resolve the crossword:LINK
List of keywords
Human impact on Climate change
extreme weather events
human activities
Increasing temperature
Release of Greenhouse gases
SUMMARY
Thawing permafrost
Decreasing of ice sheet
diminution of Albedo
Key vocabulary
click on the squares to explore the different topics.
Increased sea level
the carbon cycle
the greenhouse effect
The greenhouse effect is a process that warms the Earth. Without it, our planet would be cold, covered in ice, with no liquid water, and life would be absent from its surface.
So, we understand that the greenhouse effect is essential for life to exist. So why does it raise concern nowadays? Human activities release greenhouse gases. These gases are able to trap heat within the atmosphere, the layer of gases surrounding our planet. When the Sun’s rays reach the Earth, some of the energy is absorbed by the ground, which warms up, while another part is reflected back into space. However, when this reflected energy passes through the atmosphere, some of it is trapped and redirected back toward the surface due to greenhouse gases. As humans increase the concentration of greenhouse gases in the atmosphere, they increase the amount of heat that is retained.
As a consequence, this energy remains longer in the atmosphere and further warms the Earth. This is one of the causes of climate change.
click on the pictures to access the resources.
The carbon cycle refers to the movement of carbon atoms between different reservoirs.There are four main reservoirs on Earth: - the atmosphere (the gas layer), - the hydrosphere (the water layer), - the lithosphere (rocks and soils), - and the biosphere (living organisms). Carbon is present in the composition of many molecules. Chemical reactions occur and transform these molecules. As a result, carbon atoms move naturally from one reservoir to another through these processes. The issue is that human activities rapidly release carbon stocks that took millions of years to form: fossil fuels. Indeed, the combustion of these energy sources (oil, coal, gas) transfers carbon to the atmosphere, increasing the concentration of greenhouse gases. This disrupts the carbon cycle and contributes to global warming and climate disruption.
click on the pictures to access the resources.
Chapter 4 - Complexity of the climate system The Earth’s climate naturally varies over different timescales. However, the current increase in atmospheric CO₂ concentration is unprecedented in both speed and magnitude. As a result, the Earth’s average temperature has increased by about 1°C over the last 150 years. This evolution results from the combination of several positive feedback mechanisms, which amplify the initial warming: • The increase in greenhouse gases in the atmosphere enhances the greenhouse effect. • The melting of ice surfaces reduces the albedo, which is the fraction of solar energy reflected back into space. As ice melts, darker surfaces (oceans or land) absorb more energy, leading to further warming. • The partial melting of permafrost—ground that remains frozen for at least two consecutive years—releases additional greenhouse gases such as CO₂ and methane into the atmosphere, reinforcing the warming. The ocean plays a mitigating role by absorbing a large part of the excess heat from solar radiation. However, this leads to sea level rise, due to both: • the thermal expansion of water, and • the melting of continental glaciers. In the short term, the expansion of vegetation can act as a carbon sink, absorbing CO₂ and generating a negative feedback that slightly limits warming. Nevertheless, the accumulation of heat in the oceans makes climate change irreversible on a timescale of several centuries.
Climate system – Structured Key vocabulary 1. Causes of climate change
(What drives warming?) • Greenhouse gases (GHG) → gases that trap heat in the atmosphere (CO₂, CH₄…) • Greenhouse effect → natural process where heat is retained by the atmosphere • Melting → transformation of ice into liquid water due to warming 2. Amplifying mechanisms (Positive feedbacks)
(Processes that make warming stronger) • Positive feedback mechanisms → processes that amplify an initial change • Albedo → fraction of solar energy reflected back to space • Melting of ice → reduces albedo (decreases the amount of reflective surfaces) and increases heat absorption • Permafrost → permanently frozen ground (at least 2 years)
→ when it melts, it releases greenhouse gases (CO₂ and CH₄), reinforcing warming 3. Consequences of warming
(What happens as a result?) • Sea level rise → increase in ocean level • Thermal expansion of water → water expands when it warms • Continental glaciers → land-based ice masses that melt and add water to the oceans, increasing sea level ⚠️ Important distinction (common misconception) Sea ice (floating ice) → ice already floating on the ocean (e.g. Arctic sea ice) → its melting does NOT significantly increase sea level → because it already displaces a volume of water equal to its mass (Archimedes’ principle) 4. Regulation mechanisms
(What limits climate change?) • Carbon sink → system that absorbs more CO₂ than it releases (e.g. forests, oceans) • Negative feedback → process that reduces or stabilises a change • Mitigation / mitigating role → action or process that limits climate change
Increase of sea level (rise in sea level)
Sea level is rising mainly because of two processes linked to global warming: - Thermal expansion of water: ss ocean temperature increases, water expands. This means that even without adding more water, the volume of the oceans increases. - Melting of land ice
Glaciers and ice sheets (in Greenland and Antarctica) are melting. The water released flows into the oceans, increasing sea level. As a result, sea levels rise globally, which can lead to:
coastal flooding
erosion of shorelines
threats to coastal ecosystems and human populations.
Extreme weather events drought heatwaves flood wildfires tornados storms
Decrease of ice sheets (melting ice sheets) Ice sheets are massive layers of ice covering land, mainly in Greenland and Antarctica. Due to global warming:
air temperatures increase → surface melting
ocean temperatures increase → ice melts from below. This causes:
a loss of ice mass
a reduction in the size and thickness of ice sheets Consequences: contributes directly to sea level rise
reduces Earth’s albedo (less ice = less reflection of sunlight) → which amplifies global warming (positive feedback)
Refer to the introduction
Chapter 4: Complexity of the climate system.
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Transcript
Chapter 4: Complexity of the climate system.
Introduction
Why is the warming of the Earth a concern?
Watch the video and list the consequences of global warming.
optional: Resolve the crossword:LINK
List of keywords
Human impact on Climate change
extreme weather events
human activities
Increasing temperature
Release of Greenhouse gases
SUMMARY
Thawing permafrost
Decreasing of ice sheet
diminution of Albedo
Key vocabulary
click on the squares to explore the different topics.
Increased sea level
the carbon cycle
the greenhouse effect
The greenhouse effect is a process that warms the Earth. Without it, our planet would be cold, covered in ice, with no liquid water, and life would be absent from its surface. So, we understand that the greenhouse effect is essential for life to exist. So why does it raise concern nowadays? Human activities release greenhouse gases. These gases are able to trap heat within the atmosphere, the layer of gases surrounding our planet. When the Sun’s rays reach the Earth, some of the energy is absorbed by the ground, which warms up, while another part is reflected back into space. However, when this reflected energy passes through the atmosphere, some of it is trapped and redirected back toward the surface due to greenhouse gases. As humans increase the concentration of greenhouse gases in the atmosphere, they increase the amount of heat that is retained. As a consequence, this energy remains longer in the atmosphere and further warms the Earth. This is one of the causes of climate change.
click on the pictures to access the resources.
The carbon cycle refers to the movement of carbon atoms between different reservoirs.There are four main reservoirs on Earth: - the atmosphere (the gas layer), - the hydrosphere (the water layer), - the lithosphere (rocks and soils), - and the biosphere (living organisms). Carbon is present in the composition of many molecules. Chemical reactions occur and transform these molecules. As a result, carbon atoms move naturally from one reservoir to another through these processes. The issue is that human activities rapidly release carbon stocks that took millions of years to form: fossil fuels. Indeed, the combustion of these energy sources (oil, coal, gas) transfers carbon to the atmosphere, increasing the concentration of greenhouse gases. This disrupts the carbon cycle and contributes to global warming and climate disruption.
click on the pictures to access the resources.
Chapter 4 - Complexity of the climate system The Earth’s climate naturally varies over different timescales. However, the current increase in atmospheric CO₂ concentration is unprecedented in both speed and magnitude. As a result, the Earth’s average temperature has increased by about 1°C over the last 150 years. This evolution results from the combination of several positive feedback mechanisms, which amplify the initial warming: • The increase in greenhouse gases in the atmosphere enhances the greenhouse effect. • The melting of ice surfaces reduces the albedo, which is the fraction of solar energy reflected back into space. As ice melts, darker surfaces (oceans or land) absorb more energy, leading to further warming. • The partial melting of permafrost—ground that remains frozen for at least two consecutive years—releases additional greenhouse gases such as CO₂ and methane into the atmosphere, reinforcing the warming. The ocean plays a mitigating role by absorbing a large part of the excess heat from solar radiation. However, this leads to sea level rise, due to both: • the thermal expansion of water, and • the melting of continental glaciers. In the short term, the expansion of vegetation can act as a carbon sink, absorbing CO₂ and generating a negative feedback that slightly limits warming. Nevertheless, the accumulation of heat in the oceans makes climate change irreversible on a timescale of several centuries.
Climate system – Structured Key vocabulary 1. Causes of climate change (What drives warming?) • Greenhouse gases (GHG) → gases that trap heat in the atmosphere (CO₂, CH₄…) • Greenhouse effect → natural process where heat is retained by the atmosphere • Melting → transformation of ice into liquid water due to warming 2. Amplifying mechanisms (Positive feedbacks) (Processes that make warming stronger) • Positive feedback mechanisms → processes that amplify an initial change • Albedo → fraction of solar energy reflected back to space • Melting of ice → reduces albedo (decreases the amount of reflective surfaces) and increases heat absorption • Permafrost → permanently frozen ground (at least 2 years) → when it melts, it releases greenhouse gases (CO₂ and CH₄), reinforcing warming 3. Consequences of warming (What happens as a result?) • Sea level rise → increase in ocean level • Thermal expansion of water → water expands when it warms • Continental glaciers → land-based ice masses that melt and add water to the oceans, increasing sea level ⚠️ Important distinction (common misconception) Sea ice (floating ice) → ice already floating on the ocean (e.g. Arctic sea ice) → its melting does NOT significantly increase sea level → because it already displaces a volume of water equal to its mass (Archimedes’ principle) 4. Regulation mechanisms (What limits climate change?) • Carbon sink → system that absorbs more CO₂ than it releases (e.g. forests, oceans) • Negative feedback → process that reduces or stabilises a change • Mitigation / mitigating role → action or process that limits climate change
Increase of sea level (rise in sea level) Sea level is rising mainly because of two processes linked to global warming: - Thermal expansion of water: ss ocean temperature increases, water expands. This means that even without adding more water, the volume of the oceans increases. - Melting of land ice Glaciers and ice sheets (in Greenland and Antarctica) are melting. The water released flows into the oceans, increasing sea level. As a result, sea levels rise globally, which can lead to: coastal flooding erosion of shorelines threats to coastal ecosystems and human populations.
Extreme weather events drought heatwaves flood wildfires tornados storms
Decrease of ice sheets (melting ice sheets) Ice sheets are massive layers of ice covering land, mainly in Greenland and Antarctica. Due to global warming: air temperatures increase → surface melting ocean temperatures increase → ice melts from below. This causes: a loss of ice mass a reduction in the size and thickness of ice sheets Consequences: contributes directly to sea level rise reduces Earth’s albedo (less ice = less reflection of sunlight) → which amplifies global warming (positive feedback)
Refer to the introduction