By: Karl Philippoff Major: Earth Sciences. Why do we care? “Man’s greatest geophysical...
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Transcript of By: Karl Philippoff Major: Earth Sciences. Why do we care? “Man’s greatest geophysical...
The Carbon Cycle:Acceleration of global warming due to Carbon-
Cycle feedbacks in a coupled climate model(Cox et al., 2000)
Soil warming and Carbon-Cycle feedbacks to the Climate System
(Melillo et al., 2002)
By: Karl PhilippoffMajor: Earth Sciences
Why do we care?
• “Man’s greatest geophysical experiment” (Revelle)• Perturbing the carbon cycle• Will it stay the same? (positive/negative feedbacks)
Why do we care? Cont’d
• Releasing ~10 Gt C/yr (2010)• How much is a 1Gt C?_?_ humans _?_ Empire StateBuildings
Where is it going?
• We can only account for ~ 50% of the CO2 we release (via accounting for the use of fossil fuels and deforestation)
• sad
Bathtub analogy
𝑰𝒏𝒑𝒖𝒕=𝑶𝒖𝒕𝒑𝒖𝒕+𝑺𝒕𝒐𝒓𝒂𝒈𝒆Graphic: Nigel Holmes. Sources: John Sterman, MIT; David Archer, University of Chicago; Global Carbon Project
Short-term Carbon Cycle
Numbers in ()’s are storage terms
Input
Output
InputOutput
Large fluxes, with little net flow
Oceanic Carbon Cycle
• ‘Biological’ pump• ‘Solubility’ pump
Low HighRough indication of the productivity of oceans
Due to the fact that warm water cannot hold as much CO2 as cold water
T
solubility
Terrestrial Carbon-Cycle
• Major inputs:– Photosynthesis
• Major outputs:– Respiration
(by plants and microbes)
Cox et al. article
• Used a coupled ocean-atmosphere model and added the oceanic carbon cycle (solubility, exchange, biological pumps) and dynamic vegetation (TRIFFID)(5 functional plant types)
+ +
3 Scenarios
• All used base ocean-atmosphere model• 1)Emissions and fixed vegetation (standard
GCM)• 2)’Interactive’ CO2 and dynamic vegetation but
NO indirect effects of CO2 (Temp, H2O,etc.) only the fertilization component
• **3)Fully coupled simulation (Including all feedbacks)**
• Limitations: aerosols, large-scale ocean, no deforestation
Fully coupled resultsPast Projected
Net source
Net sink0 No change
Cox et al, Fig. 2
Rates from 19502000 are comparable to observations
Results:1) Airborne
fraction increases from ½ ~ ¾
2) Land becomes source ~ 2050
Source and sink values determined with respect to 1860
Wait…what happens around 2050?• Photosynthesis usually increases
when CO2 concentrations increase (fertilization), assuming other resources are not limiting (sink/input)
• Plant maintenance (respiration) and microbial respiration increase with temperature (source/output)
• Around 2050, outputs begin to exceed inputs, reducing terrestrial carbon storage
Before 2050
After 2050
+ -
Results, cont’d
• a
Cox et al., Fig 4
Amazon
Blue arrows show difference between climate feedback due indirect and direct effects of CO2 at GLOBAL scale(model runs 2 and 3)
Green arrows show difference between two model runs for South America
Climate feedbacks completely change the terrestrial carbon cycle, especially in the Amazon and for soil microbes
For scale, the change in soil carbon between the two runs is roughly ~2X our cumulative CO2 emissions (~290Gt C)
Carbon stored in Vegetation
Soil Carbon
Total CO2 emissions(2004)
Oceanic carbon cycle
• Oceans show saturation effect at high CO2• Partially caused by– Non-linear dependence of total ocean carbon
concentration to atmospheric carbon– Slower ocean circulation (-25%)– Thermal stratification reduces upwelling, causing
primary productivity to decrease ~5%
And the results of this are…?
• A
• In 2100, [CO2] = 980 ppmv (250ppm > standard)• Average land temperatures increase 8K (5.5K standard)
1
Cox et al, Fig. 3
2
3
1
2
3
Equivalent of moving from Columbus (11) Gainesville, FL (20) or Houston, TX (21)
Melillo et al. study• Harvard Forest• Took soil CO2 fluxes (91-00)• Nitrogen mineralization (91-98)
6m
6m
Heating cables
Used 6 similar plots
+5C
Results:
𝐶𝑟𝑒𝑙𝑒𝑎𝑠𝑒𝑑(𝐻𝑒𝑎𝑡𝑒𝑑−𝐷𝑖𝑠𝑡𝑢𝑟𝑏𝑎𝑛𝑐𝑒𝐷𝑖𝑠𝑡𝑢𝑟𝑏𝑎𝑛𝑐𝑒 )∗100
Increased soil CO2 flux
Large Δ Small to no Δ
Back to normal
Melillo et al, Fig.1
~80% of respiration due to soil microbes
Soil CO2 fluxes
What does that mean?
• Two-pool model
Total amount of carbon stored in soil
Small amount of carbon (~10%) that is easily broken down by microbes (polysaccharides)Sensitive to Temperature
Large amount of carbon (~90%) that is more difficult (aromatic rings)Insensitive to Temperature
Results, cont’d
• ad
Melillo et al., Fig.3
Large increase in usable nitrogen
Large, consistent increase in usable N
This increase had no effect on loss processes (leaching or gaseous) and led to a total increase of 41 g/m^2
Mineralized Nitrogen is in the form NH4+, or NO3-
Many mid-latitude forests are nitrogen-limited
Results, cont’d
Net:
CO2 release due to increase in respiration by
microbes-944 g/m2+ ~1500 g/m2
CO2 uptake due to increased N mineralization
∆𝐶𝑡𝑜𝑡𝑎𝑙=𝐶 𝑓𝑖𝑥𝑒𝑑−𝐶𝑟𝑒𝑠𝑝𝑖𝑟𝑒𝑑
= (1500 g/m2) –(944 g/m2)
=556 g/m2 Or ~60% greater than the Δ in respiration
(measured in a different study in the same area)
Caveats to study:• Would also be affected by other quantities tied to
climate change such as: (effect on CO2 flux in())– Water availability (+ with increase, - with decrease)– Temperature effects on plant photosynthesis and
respiration (+/-)– Increase in concentration of CO2 (+)– Also warming will probably have its largest effects
on high-latitude ecosystems (large amounts of C)
In Summary…
• Carbon cycle is complex with many portions, both in the terrestrial and oceanic components
• The presence of a multiplicity positive (decrease in soil carbon) and negative (increase in biomass) feedbacks make it difficult to predict how it will respond in the future
• Not only this, but some signal to noise problems as well
What I think…• As the papers demonstrate, there is still large
uncertainties associated with following our excess carbon after it exits the atmosphere.
• Very interesting to see the 2 papers more or less contradict each other.
• Future directions: – Still have little idea of the controls of the controls on primary
productivity and respiration in global sense (biomes, species) and how they would respond to a change in their environment (and we don’t know how that will change either… (Amazon from paper #1) (like to trying to hit a moving target )
– Explicit modeling of such complexity has only just begun, and with all the feedbacks in play, it will probably take some time to get a good handle on it
Questions?