ENVS10011 Lecture Notes - Lecture 6: Carbon Sink, Soil Carbon, Carbon Footprint
17 May 2018
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WEEK 6: ROLE OF ENVIRONMENTS IN CARBON AND CLIMATE
CHANGE MITIGATION
Carbon Sequestration: process by which CO2 is removed from the atmosphere + stored in
soil or vegetation
Gross Emissions: all, including methane + N2O (in CO2equivalents)
Net Emissions: gross emissions – sequestration
• Of concern to policy + IPCC
• Emission Intensity: carbon footprint, efficiency metric
• Carbon Farming:
o Increased storage of carbon in soil or trees
o Minimising methane + nitrous oxide losses, while improving efficiency
• Carbon Neutral: if a good/service has zero carbon emissions
o Gross emissions – sequestration = zero or negative
The Carbon Cycle
• Not natural anymore, greatly influenced by human activity
• Sink capacity of natural CO2 sinks decreasing (results in increase atmospheric CO2)
o Even lower in human managed environments
• Forests: greatest terrestrial carbon sinks
o Globally soils store more C than biomass
• Capacity of an ecosystem to store C is determined by balance of C uptake
(photosynthesis) + C loss (respiration)
• Agriculture = source + sink for carbon
• Large carbon pools have relatively small fluxes
• Ocean = largest carbon sink, atmosphere accumulating more each year
• More carbon emissions than carbon uptake (due to fossil fuel emissions)
• Increased carbon sinks (increase terrestrial plant or soil sinks)
Gross Primary Productivity (GPP) (photosynthesis): how much carbon is ‘fixed’ each time
period
Canopy, wood + root CO2 respiration (Ra): releases carbon dioxide
Net Primary Productivity = GPP – Ra (real input into the ecosystem of carbon)
• Other things to consider: soil microbial respiration (Rh), decomposition, litter (make soil
carbon), non- CO2GHG (trace gas exchange)
Net Ecosystem Productivity (NEP) = GPP – Ra – Rh
• May be zero, if ecosystem in carbon equilibrium
Carbon Stocks/Pools: amount of Carbon at one point in time
Carbon Sequestration: change in stock of C over time
Forest Carbon
• Produce most terrestrial carbon, crops mainly aboveground
• Assumption half of productivity is underground
• Atmospheric CO2 concentrations: overall trend increasing over time at all latitudes
o Large seasonal variation mainly in Northern Hemisphere: deciduous or highly
seasonal trees/ecosystems
o Less in Southern Hemisphere: less seasonal plants/ecosystems, less forests
Document Summary
Week 6: role of environments in carbon and climate. Carbon sequestration: process by which co2 is removed from the atmosphere + stored in soil or vegetation. Gross emissions: all, including methane + n2o (in co2equivalents) Net emissions: gross emissions sequestration: of concern to policy + ipcc, emission intensity: carbon footprint, efficiency metric, carbon farming: Increased storage of carbon in soil or trees: minimising methane + nitrous oxide losses, while improving efficiency, carbon neutral: if a good/service has zero carbon emissions, gross emissions sequestration = zero or negative. Gross primary productivity (gpp) (photosynthesis): how much carbon is fixed" each time period. Canopy, wood + root co2 respiration (ra): releases carbon dioxide. Net primary productivity = gpp ra (real input into the ecosystem of carbon: other things to consider: soil microbial respiration (rh), decomposition, litter (make soil. Increased carbon sinks (increase terrestrial plant or soil sinks) carbon), non- co2ghg (trace gas exchange)
