Intro to Climate Science Unit 6 Review: Carbon Cycle and Ecosystems

Key Concepts

• Carbon is a fundamental element for life on Earth found in all organic compounds
• The carbon cycle describes the movement of carbon through the Earth's systems (atmosphere, biosphere, geosphere, hydrosphere)
• Photosynthesis and respiration are key biological processes in the carbon cycle
  • Photosynthesis converts CO2 into organic compounds using sunlight energy (glucose)
  • Respiration breaks down organic compounds releasing CO2 back into the atmosphere
• Carbon sinks are reservoirs that absorb and store more carbon than they release (oceans, forests)
• Carbon sources are reservoirs that release more carbon than they absorb (fossil fuel combustion, deforestation)
• Human activities have significantly altered the natural carbon cycle leading to increased atmospheric CO2 levels
• Rising atmospheric CO2 concentrations contribute to global warming and climate change

Carbon Cycle Basics

• The carbon cycle is a biogeochemical cycle that exchanges carbon among Earth's spheres
• Carbon moves through the Earth's systems in various forms: CO2 gas, organic compounds, carbonate rocks
• The main processes in the carbon cycle include photosynthesis, respiration, decomposition, and combustion
• Photosynthesis removes CO2 from the atmosphere converting it into organic compounds stored in biomass
• Respiration and decomposition release CO2 back into the atmosphere as organisms break down organic matter
• Weathering of rocks and volcanic eruptions also release CO2 into the atmosphere
• The ocean absorbs atmospheric CO2 through gas exchange at the surface and biological processes
  • Dissolved CO2 in the ocean can form carbonic acid (H2CO3) leading to ocean acidification

Ecosystem Components

• Ecosystems are composed of biotic (living) and abiotic (non-living) components that interact
• Primary producers (plants, algae) convert CO2 into organic compounds through photosynthesis forming the base of food webs
• Consumers (animals) obtain carbon by eating other organisms and release CO2 through respiration
• Decomposers (bacteria, fungi) break down dead organic matter releasing nutrients and CO2 back into the system
• Soil organic matter stores large amounts of carbon from dead plant and animal remains
• Aquatic ecosystems (oceans, lakes, rivers) play a significant role in the carbon cycle
  • Phytoplankton are important primary producers in aquatic ecosystems
• Terrestrial ecosystems (forests, grasslands) store carbon in biomass and soil

Carbon Sinks and Sources

• Carbon sinks are reservoirs that absorb and store more carbon than they release
  • Examples of carbon sinks include oceans, forests, and soil
• Oceans are the largest active carbon sink absorbing about 25% of anthropogenic CO2 emissions
• Forests absorb CO2 through photosynthesis and store carbon in biomass and soil
  • Deforestation reduces the capacity of forests to act as carbon sinks
• Carbon sources are reservoirs that release more carbon than they absorb
• Fossil fuel combustion (coal, oil, natural gas) is the primary anthropogenic carbon source
• Deforestation and land-use changes release stored carbon from biomass and soil into the atmosphere
• Permafrost thaw can release stored carbon from previously frozen organic matter
• Volcanic eruptions release CO2 into the atmosphere but are a minor source compared to human activities

Human Impact on the Carbon Cycle

• Human activities have significantly altered the natural carbon cycle since the Industrial Revolution
• Burning fossil fuels releases ancient stored carbon into the atmosphere increasing CO2 levels
• Deforestation removes important carbon sinks and releases stored carbon from biomass and soil
• Land-use changes (agriculture, urbanization) can reduce the capacity of ecosystems to store carbon
• Cement production releases CO2 through the chemical process of calcination
• Livestock farming contributes to methane (CH4) emissions, a potent greenhouse gas
• Anthropogenic CO2 emissions have increased atmospheric CO2 levels from ~280 ppm (pre-industrial) to over 410 ppm today
• The rate of CO2 increase in the atmosphere is unprecedented in Earth's recent history

Climate Change Connections

• The carbon cycle is closely linked to Earth's climate system
• Atmospheric CO2 is a greenhouse gas that absorbs and re-emits infrared radiation warming the Earth's surface
• Rising atmospheric CO2 levels due to human activities are the primary driver of current climate change
  • CO2 levels have increased from ~280 ppm (pre-industrial) to over 410 ppm today
• Positive feedback loops can amplify the effects of climate change on the carbon cycle
  • Example: Warmer temperatures can thaw permafrost releasing stored carbon and further increasing atmospheric CO2
• Climate change impacts ecosystems' ability to absorb and store carbon (ocean acidification, forest dieback)
• Changes in the carbon cycle can affect the magnitude and rate of future climate change

Measuring and Modeling

• Measuring carbon fluxes helps quantify the movement of carbon through Earth's systems
• The Keeling Curve, measured at Mauna Loa Observatory, shows the steady increase in atmospheric CO2 since 1958
• Carbon isotope ratios (12C, 13C) can help distinguish between natural and anthropogenic CO2 sources
• Eddy covariance towers measure CO2 exchange between ecosystems and the atmosphere
• Remote sensing (satellites) can monitor changes in forest cover and primary productivity
• Carbon cycle models simulate the complex interactions and feedbacks within the Earth's systems
  • Models help predict future atmospheric CO2 levels and climate change scenarios
• Integrated assessment models (IAMs) combine carbon cycle, climate, and socio-economic factors to inform policy decisions

Future Implications

• Continued anthropogenic CO2 emissions will further increase atmospheric CO2 levels and exacerbate climate change
• Limiting global warming to 1.5-2°C (Paris Agreement) requires significant reductions in CO2 emissions
• Negative emissions technologies (carbon capture and storage, afforestation) may be necessary to remove CO2 from the atmosphere
• Protecting and restoring carbon sinks (forests, wetlands) is crucial for mitigating climate change
• Ocean acidification threatens marine ecosystems and the ocean's capacity to absorb CO2
• Climate change impacts (droughts, fires, pests) can reduce the carbon storage capacity of ecosystems
• Adapting to and mitigating the impacts of climate change on the carbon cycle is a major challenge facing society
• Transitioning to a low-carbon economy and sustainable land management practices is essential for stabilizing the carbon cycle