3.4 Atmospheric Carbon and Climate Feedbacks
2 min read•july 25, 2024
Earth's atmosphere acts as a blanket, trapping heat through the . Carbon dioxide, a key player, has increased dramatically since pre-industrial times. This rise impacts Earth's energy balance, triggering various that can amplify or dampen warming effects.
The involves natural and human-made sources and sinks, with CO2 moving between reservoirs. Historical records show a strong link between atmospheric carbon and global temperatures. Understanding these relationships is crucial for predicting future climate scenarios and potential .
Atmospheric Carbon and Climate System
Greenhouse effect and carbon dioxide
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- Greenhouse effect traps heat in Earth's atmosphere maintaining habitable temperatures
- Greenhouse gases include CO2, CH4, H2O, and N2O absorb and re-emit infrared radiation
- CO2 primary anthropogenic greenhouse gas with long atmospheric lifetime
- measures greenhouse gas impact on Earth's energy balance (W/m²)
- Atmospheric CO2 concentration increased from ~280 ppm (pre-industrial) to >410 ppm (current)
- Greenhouse effect mechanism:
- Solar radiation passes through atmosphere
- Earth's surface absorbs and re-emits energy as infrared radiation
- Greenhouse gases trap outgoing infrared radiation
- Trapped heat warms lower atmosphere and surface
Climate feedbacks in carbon cycle
- Climate feedbacks amplify or dampen effects of climate forcings
- Positive feedbacks (amplifying):
- Water vapor feedback increases greenhouse effect as warmer air holds more moisture
- Ice-albedo feedback decreases reflectivity as melting ice exposes darker surfaces (Arctic sea ice)
- Permafrost thaw releases stored carbon as CO2 and CH4 (Siberian tundra)
- reduces ocean's capacity to absorb CO2
- Negative feedbacks (dampening):
- Enhanced plant growth increases carbon sequestration through higher rates (Amazon rainforest)
- Increased rock weathering removes CO2 from atmosphere as temperatures rise (Himalayan mountains)
- Cloud formation reflects more solar radiation due to increased evaporation and low-level cloud cover
Carbon Cycle and Climate Change
Sources and sinks of atmospheric carbon
- Natural carbon sources release CO2 through volcanic eruptions, respiration, wildfires, and ocean outgassing
- Natural carbon sinks absorb CO2 via photosynthesis, ocean absorption, sediment formation, and rock weathering
- Anthropogenic carbon sources emit CO2 from (coal, oil, natural gas), , cement production, and agricultural practices
- store carbon in atmosphere, oceans, terrestrial biosphere, and lithosphere
- measures movement of carbon between reservoirs in gigatons of carbon per year (GtC/yr)
Atmospheric carbon vs global temperature
- shows steady increase in atmospheric CO2 concentrations since 1958
- Paleoclimate records (ice cores, tree rings, sediment cores) reveal historical CO2-temperature correlation
- measures global temperature response to doubling of CO2 (℃)
- Radiative forcing equation: calculates change in radiative forcing
- Temperature response equation: estimates change in global mean temperature
- Tipping points represent thresholds for rapid climate system changes (Arctic sea ice loss, Amazon rainforest dieback)
- Climate projections use global (GCMs) to forecast future scenarios based on emission pathways and feedback mechanisms
Key Terms to Review (20)
Carbon accounting: Carbon accounting refers to the process of measuring and tracking the amount of carbon dioxide emissions produced and removed from the atmosphere, allowing for a better understanding of greenhouse gas contributions to climate change. This systematic approach helps identify sources and sinks of carbon, which is critical for developing strategies to reduce emissions and mitigate climate impacts. It plays a vital role in informing policy decisions and assessing progress toward climate goals.
Carbon cycle: The carbon cycle is the series of processes through which carbon atoms circulate in the Earth's systems, including the atmosphere, biosphere, hydrosphere, and geosphere. This cycle plays a crucial role in regulating Earth’s climate, supporting life, and maintaining ecological balance by involving various reservoirs and fluxes of carbon across different spheres.
Carbon dioxide (CO2): Carbon dioxide (CO2) is a colorless, odorless gas that is a natural part of Earth's atmosphere, primarily produced by the respiration of living organisms and the combustion of fossil fuels. This greenhouse gas plays a crucial role in climate feedback mechanisms, as it traps heat in the atmosphere and contributes to global warming and climate change.
Carbon flux: Carbon flux refers to the movement of carbon in and out of various carbon reservoirs in the Earth system, including the atmosphere, oceans, soil, and living organisms. It is a key process that influences the global carbon cycle, helping to regulate atmospheric carbon dioxide levels and, consequently, climate change. Understanding carbon flux is crucial for recognizing how different processes, such as photosynthesis and respiration, contribute to the overall balance of carbon in the environment.
Carbon reservoirs: Carbon reservoirs are natural systems that store carbon in various forms, such as organic matter, fossil fuels, and dissolved carbon dioxide in oceans. They play a crucial role in the global carbon cycle by regulating the movement and concentration of carbon dioxide in the atmosphere, thus influencing climate change and feedback mechanisms.
Climate feedbacks: Climate feedbacks refer to processes that can amplify or dampen the effects of climate change, influencing the overall climate system. These feedbacks can occur through various mechanisms, including changes in temperature, greenhouse gas concentrations, and land surface characteristics. Understanding these feedbacks is crucial as they play a significant role in determining the trajectory of climate change and its impacts on ecosystems and human societies.
Climate models: Climate models are sophisticated computational tools used to simulate and understand the Earth's climate system and predict future climate changes. These models integrate various components, including the atmosphere, oceans, land surface, and ice, to provide insights into how different factors, like greenhouse gas emissions, influence global temperatures and weather patterns over time. They are essential for assessing potential impacts on ecosystems, human health, and economies as well as evaluating mitigation strategies against climate change.
Climate sensitivity: Climate sensitivity refers to the measure of how much the Earth's average surface temperature is expected to increase in response to a doubling of atmospheric carbon dioxide (CO₂) concentration. This concept is crucial for understanding the long-term impacts of greenhouse gas emissions on global temperatures and helps in evaluating climate feedback mechanisms that can amplify or dampen these temperature changes.
Deforestation: Deforestation is the large-scale removal of trees from forests or other lands, typically resulting in damage to the quality of the land. This process significantly alters carbon reservoirs, influencing global carbon cycles and impacting various ecosystems, climate regulation, and biogeochemical processes.
Fossil fuel combustion: Fossil fuel combustion refers to the burning of coal, oil, and natural gas to produce energy, resulting in the release of carbon dioxide (CO2) and other greenhouse gases into the atmosphere. This process not only contributes significantly to the global carbon cycle but also affects other biogeochemical cycles by altering nutrient dynamics and atmospheric chemistry.
Global warming: Global warming refers to the long-term increase in Earth's average surface temperature due to human activities, primarily the emission of greenhouse gases such as carbon dioxide and methane. This rise in temperature is linked to various atmospheric changes and climate feedback mechanisms that can amplify or mitigate its effects on ecosystems and weather patterns.
Greenhouse effect: The greenhouse effect is the process by which certain gases in Earth's atmosphere trap heat, preventing it from escaping into space, and thus warming the planet. This natural phenomenon is crucial for maintaining a habitable climate, but human activities have intensified it by increasing the concentration of greenhouse gases, leading to global warming and climate change.
Keeling Curve: The Keeling Curve is a graph that represents the concentration of atmospheric carbon dioxide (CO2) over time, measured at the Mauna Loa Observatory in Hawaii since 1958. It illustrates the ongoing increase of CO2 levels due to human activities like fossil fuel combustion and deforestation, while also showing seasonal fluctuations linked to natural processes. This curve is crucial in understanding the relationship between carbon emissions and climate change.
Methane (CH₄): Methane (CH₄) is a potent greenhouse gas composed of one carbon atom and four hydrogen atoms. It is a key player in atmospheric carbon dynamics, with a global warming potential significantly greater than carbon dioxide over a short time frame. Methane's role in climate feedback mechanisms can influence temperature changes and various environmental processes, making it critical to understanding climate change.
Negative Feedback: Negative feedback is a process in which a system responds to a change by initiating responses that counteract the initial change, thus maintaining equilibrium or stability. This concept is crucial in understanding how various components of Earth’s systems interact, as it helps to regulate processes across different spheres and biogeochemical cycles, playing a significant role in climate dynamics and atmospheric conditions.
Ocean acidification: Ocean acidification refers to the process by which the ocean becomes more acidic due to increased absorption of carbon dioxide (CO2) from the atmosphere. This phenomenon has significant implications for marine ecosystems, carbonate chemistry, and global biogeochemical cycles.
Photosynthesis: Photosynthesis is the biological process through which green plants, algae, and some bacteria convert light energy, usually from the sun, into chemical energy stored in glucose. This process is essential for producing oxygen and organic compounds that serve as food for various organisms, linking it to vital ecological and biogeochemical cycles.
Positive Feedback: Positive feedback refers to a process in which an initial change in a system triggers further changes that amplify or enhance the original effect. This dynamic can lead to a runaway effect, where the impact becomes increasingly significant, often resulting in dramatic shifts in environmental conditions or biogeochemical processes.
Radiative Forcing: Radiative forcing refers to the change in energy balance in the Earth's atmosphere due to factors like greenhouse gases, aerosols, and solar radiation. It measures the influence of these factors on the climate system, with positive forcing leading to warming and negative forcing leading to cooling. Understanding radiative forcing is crucial for assessing how different substances, such as aerosols and trace gases, impact global temperature and climate feedback mechanisms.
Tipping points: Tipping points are critical thresholds where a relatively small change can lead to significant and often irreversible effects within a system. In environmental and climate contexts, these moments can signify shifts in ecosystems or climate patterns that trigger drastic changes, impacting feedback loops, carbon cycling, and overall Earth system dynamics.