Carbon Cycle Flashcards
Why do we want to measure CO2 in somewhere like Mauna Loa - Hawaii?
- Measuring in Leeds would just give you a measure of the emissions in that area
- Want to measure the background level or CO2 - to see its change over time
How does CO2 emissions vary annually and seasonally?
- Keeling curve
- Get seasonal cycle that is modulated by photosynthesis - stronlgly controlled by higher amount of vegetation in the northern hemisphere
- So Max CO2 in April - build up over winter
- Min CO2 in Sep/Oct - from high photosynthesis in summer
Summarise a simplified carbon cycle
- CO2 into plants - photosynthesis
- Autotrophic and heterotrophic respiration and decay - CO2 into atmosphere
- Sea-surface gas exchange - controlled by relative CO2 - carbon into deep ocean
What are the two main fluxes between the land and atmosphere?
- Atmosphere -> land (photosynthesis)
- Land -> atmosphere (respiration)
What are some of the additional fluxes caused by humans?
- Fossil fuel combustion
- Land use change
- Only about 45% of carbon remains in atmosphere - rest is taken up by carbon sinks
How does land use change affect carbon emissions and surface temperature?
- Release of carbon into atmosphere from removal of forests
- But change in albedo due to land use change has a higher reflectivity, and a negative radiative forcing and therefore a cooling effect
What is the global carbon budget CO2 emissions made up of?
= CO2 growth + CO2 sinks
How did land sinks used to be calculated?
It used to be inferred as residual - but it is increasing now
Name 4 key feedbacks of the changing biosphere
- Land use change: regrowing northern forests, fire suppression, wood encroachment
- CO2 and nitrogen fertilization
- Diffuse/direct radiation changes - aerosols
- Climate change - more photosynthesis, higher temps, longer growing seasons, drought/rain cyles
What are the two broad categories for studying the carbon cycle?
Measurements - e.g., forest inventories, fluxes, aircraft and satellitle observations:
- Biomass changes
- Atmospheric CO2 and other trace gases (CH4)
- NEE fluxes
Models:
- Land surface models
- Ocean models
- Atmospheric transport models
- Coupled earth system models
What is a bottom-up study?
Measuring trees directly - from forest inventory data
- Can derive fluxes from long-term ecosystem carbon studies
What is terrestrial laser scanning?
Reconstructs 3D structure of trees for accurate assessment of volume
- Can be combined with traditional allometric methods to compare how much carbon is stored in these woodlands
How is atmospheric CO2 measured globally?
Using programs:
- Observatories across globe - to measure atmospheric CO2
- e.g., Mauna Loa observatory
What different fluxes can we measure, and how can we measure them?
GPP: gross primary productivity - flux of carbon from the atmosphere into the ecosystem
TER: terrestrial ecosystem respiration - sum of autotrophic (plant) and heterotrophic (soil) respiration
NEE: net ecosystem exchange: NEE = TER -GPP:
- < 0 for carbon sink
- > 0 for carbon source
Can measure this using Eddy Covariance measurements
Give an example for sensing the presence of vegetation - optical remote sensing of vegetation?
Normalised difference vegetation index (NDVI)
- Leaves absorb red visible light, but reflect near IR radiation
- So looks at ratio between absorbed and reflected radiation between these two
- Values range between -1 to +1 (+1 = healthy vegetation)
