Biosphere Lecture 7

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Which is the most important model in the model hierarchy (uses the most factors)
Earth System Model
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Unknowns in future global warming are usually assumed to arise from uncertainties either in the amount of
anthropogenic greenhouse gas emissions or in the sensitivity of the climate to changes in greenhouse gas concentrations
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To date, these models indicate that the relevant carbon cycle uncertainties are smaller than the
uncertainties in physical climate feedbacks and emissions. Here, for a single emissions scenario, we use a full coupled climate–carbon cycle model and a systematic method to explore uncertainties in the land carbon cycle feedback. We find a plausible
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The sensitivity of photosynthetic metabolism to temperature emerges as the most important
uncertainty.
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This highlights an aspect of current land carbon modelling where there are open questions about the potential role of plant acclimation to increasing temperatures. There is an urgent need for better understanding of plant photosynthetic responses to
high temperature, as these responses are shown here to be key contributors to the magnitude of future change.
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Carbon reservoirs in Petagrams of Carbon (PgC) =
1015 grams
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how can we tell where is the carbon going?
Detailed site measurements Biomass surveys Global networks Eddy covariance towers Flask sampling Satellites
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GPP
Gross Primary Productivity
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NPP
Net Primary Productivity
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Gross primary productivity (GPP)
is the rate at which plants take up CO2 and produce carbohydrates through the process of photosynthesis.
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Net primary productivity (NPP)
rate at which plants in an ecosystem produce biomass; it is equal to the difference between GPP and the rate of autotrophic respiration.
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Autotrophic respiration (Ra
is the rate at which carbon is returned to the atmosphere as CO2 during plant metabolism
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Heterotrophic respiration (Rh)
) is the release of CO2 during the process of decomposition of organic matter in the soil by soil animals, fungi, and other decomposer microorganisms. 
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Autotroph:
an organism that can produce organic matter from simple substrates present in its surroundings using another energy source (light in the case of plants
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Heterotroph:
: an organism that cannot fix its own carbon and therefore has to consume organic matter for its growth
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NPP =
= GPP – Ra
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Total ecosystem respiration (Rtotal)
Rtotal = Ra + Rh
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Net Ecosystem Productivity (NEP)
NEP = GPP – Rtotal
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Net biome productivity (NBP)
NBP = GPP – Rtotal – disturbance
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Biomass measurements
Tree diameter at breast height is the key measurement Use equations to estimate total above- ground biomass and total below- ground biomass Consider biomass to be ~50% carbon
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Diameter at breast height, or DBH, is a standard method of expressing the
the diameter of the trunk or bole of a standing tree. DBH is one of the most common dendrometric measurements.
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Tree trunks are measured at the height of an adult's breast, which is defined differently in different countries and situations. In continental Europe, Australia, the UK, and Canada the diameter is measured at
1.3 metres
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Harvest method
Use of litter bags to collect all litter produced over a certain period of time. Good for: Long term measurements of litter production. Unexpensive. Limitations: Neglects root litter production, high uncertainty in upscaling.
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Chamber methods
Measurement of respiration (R total) – dark chambers + Infra Red Gas Analyser - Measurement of Net Ecosystem Productivity (NEP) – clear chambers + IRGA The difference between them: GPP
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Advantages and disadvantages of chamber methods
Good for: separating different fluxes, it is detailed. Limitations: more expensive, issues of upscaling.
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Eddy covariance works on
3D wind data CO2 concentrations Compare up-drafts and down-drafts Work out if carbon is being absorbed or released
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Eddy convariance used
sonic anemoter (3d wind speeds) and infra-red gas analyser (CO2 concentration)
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Advantages and disadvanatages of eddy convariance
Totally automated, records continuously day and night. Measures NEP and Rtot. Good in flat terrain, homogenous or heterogeneous vegetation, it is non-intrusive. Good for upscaling Limitations: does not do well on sloping ground, or very still conditi
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Fluxnet shows the
location of towers
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What is Remote Sensing (RS)?
“The acquisition of physical data of an object without touch or contact” (Lintz and Simonett, 1976) “The observation of a target by a device some distance away” (Barrett and Curtis, 1982)
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How does remote sensing work?
All objects absorb, reflect and transmit different wavelengths of energy called electromagnetic radiation (includes visible light) Remote sensing detects and analyses this electromagnetic energy Can detect live plant biomass based on the wavelengths
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NDVI:
normalised difference vegetation index
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The normalized difference vegetation index (NDVI) is a
simple graphical indicator that can be used to analyze remote sensing measurements, typically but not necessarily from a space platform, and assess whether the target being observed contains live green vegetation or not.
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Biomass measurements in African forests indicate
carbon storage is increasing Tree biomass in 2007 is greater than in 1968
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The Arctic is getting greener ...
Satellite data shows an overall increase in plant growth in the Arctic Rapid warming means the Arctic is already changing It is ‘greening’
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International tundra experiment (ITEX)
Perspex chambers Passive warming Increased temperature inside by 1-2oC
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Tundra responses to warming
Most vascular plants grew better at higher temperatures Some groups out-competed
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Soil organic matter decomposition
In situ warming increases the rate of soil organic matter decomposition Switching warming on and off demonstrates the role temperature plays
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Rainfall manipulation in the tropics
Excluded 50% of rainfall from large plots in the Amazon and measured tree responses after 7 years
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Predictions for the tropics to get drier. Consequence of drying seem to be
lose biomass.
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Free Air Carbon Dioxide enrichment aka
FACE
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Impacts of elevated CO2
The most important result related to DMP (dry matter production) The stimulation was greatest for trees.
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MODELING: Responses to elevated CO2
Models indicate that elevated carbon dioxide concentrations will substantially increase carbon uptake by the land surface This limits the amount of carbon dioxide which accumulates in the atmosphere
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Global patterns in change in climate and plant growth:
Uncertain whether plant growth will increase or decrease in a warmer world Some models predict increased growth Others predict substantial reductions in plant growth
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Soil carbon storage
All models predict a reduction in the mean residence time of carbon in soils The organic matter is decomposing faster If warming does not increase plant growth this should result in a loss of soil C In high lat peatlands: warming accelerates
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What is the Convention on Biological Diversity?
Signed by 150 government leaders at the 1992 Rio Earth Summit, the Convention on Biological Diversity is dedicated to promoting sustainable development. Conceived as a practical tool for translating the principles of Agenda 21 into reality, the Conve
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The JNCC
has also developed a list of indicator species for the UK JNCC is a statutory adviser to UK Government and devolved administrations
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Card 2

Front

Unknowns in future global warming are usually assumed to arise from uncertainties either in the amount of

Back

anthropogenic greenhouse gas emissions or in the sensitivity of the climate to changes in greenhouse gas concentrations

Card 3

Front

To date, these models indicate that the relevant carbon cycle uncertainties are smaller than the

Back

Preview of the front of card 3

Card 4

Front

The sensitivity of photosynthetic metabolism to temperature emerges as the most important

Back

Preview of the front of card 4

Card 5

Front

This highlights an aspect of current land carbon modelling where there are open questions about the potential role of plant acclimation to increasing temperatures. There is an urgent need for better understanding of plant photosynthetic responses to

Back

Preview of the front of card 5
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