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Identifying and Reducing Uncertainties in the Global Carbon Cycle
I am broadly interested in interactions between Earth’s climate and biogeochemical cycles. More specifically I am interested in physical factors that may limit the Earth’s capacity to take up future C emissions. Identify the pools and their relative size…C, Water, and Nutrients. As we continue to emit C from fossil fuels. However, the global C and H2O are inextricably linked through photosynthesis. Ashley Ballantyne University of Montana
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Topics of Discussion Energy and CO2 Emissions in Montana: where does our energy come from? Recent trends in US CO2 emissions: where are we headed? Global trends and uncertainties in CO2 emissions: 400 ppm: here we come! An audit of the global C cycle: how much CO2 remains in the atmosphere? Physical mechanisms of biosphere-atmosphere exchange…NOVEL application of carbon isotopes in the biosphere and atmosphere. Investigate sensitivity global C cycle to warming comparing different stomatal conductance models. Audit of the global C cycle…identify major sources of UNCERTAINTY and look at changes in CARBON UPTAKE over time. Lastly discuss climate feedbacks and uncertainty. 2 2
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Where does our energy come from in Montana?
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Energy Map of Montana The Bakken shale under Montana and North Dakota, one of the largest accumulations of crude oil in the United States, As of the end of 2010, Montana held over one-quarter of the estimated recoverable reserve base of coal in the United States and was the sixth largest coal-producing State in 2011 Wind electric power generation grew by 34 percent in 2011 and supplied 4.2 percent of State's net electricity generation. Montana has created a Renewable Portfolio Standard for all electricity suppliers to be capable of generating 15 percent of electricity from renewable energy resources by 2015.
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CO2 emissions in the US: cautiously optimistic
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The Green Bounce: CO2 emission decrease GDP increase
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Decrease in reliance on coal
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Decrease in industrial emissions
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CO2 Emission Animations
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Economic Drivers of Fossil Fuel Emissions
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CO2 Emissions adjusted for consumption
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Fossil Fuels:net importers (red) Net Exporters (blue) Traded Goods Net effect on Emissions
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Net Import/Export Emissions
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Errors in Chinese emission estimates lead to global uncertainty
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A recap on the global carbon budget
Approximately 50% of the fossil fuel emissions are taken up by land and ocean carbon reservoirs (e.g. ‘sinks’). Almost all of the carbon taken up by the land during photosynthesis is returned to the atmosphere as autotrophic or heterotrophic respiration. Almost all of the carbon taken up by the ocean during air-sea gas exchange is returned to the atmosphere. Define Units : The fluxes are measured in billion tons (PgC) Look at two main reservoirs (aka sinks) the ocean and land. Talk about net exchange and fraction that is taken up by sinks 50% Lastly discuss climate feedbacks and uncertainty.
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Uncertainty in carbon-climate feedbacks
Land Uptake Uncertainty in the coupled carbon- climate system is comparable to uncertainty from aerosols and cloud forcing. Most of this uncertainty is due to complex interactions among processes in the terrestrial biosphere. Ocean Uptake Carbon sinks represent the Earth’s capacity to take up a fraction of C emitted; however, these C sinks are not limitless. In fact, these C sinks on land and in the ocean are predicted to reverse in the coming century becoming sources. Explain briefly cloud and aerosol uncertainties. Most of the uncertainty resides in the terrestrial biosphere…Therefore how plants respond to increased CO2 may have a huge impact on future climate warming. (Freidlingstein et al. Environmental Sustainability, 2010)
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An audit of the global carbon budget
Is there any evidence of a decrease in carbon uptake at the global scale? What are the physical mechanisms regulating the exchange of carbon and water between the biosphere and atmosphere? How are these physical mechanisms expected to change under future climate warming? Have these physical mechanisms started to limit the Earth’s capacity to take up C as a result of climate change? THEORY PREDICTS THAT WE SHOULD SEE A DECREASE IN C UPTAKE IN RESPONSE TO WARMING. 17 17 17
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Diagnostics of the global carbon cycle
Global Carbon Budget: dCa dt = ΣF + ΣN Net Global Uptake (ΣN): dCa dt ΣN = ΣF Cover global carbon cycle fluxes FF (well known) and LU, Land Mass Balance Eqn describing these fluxes Isotopic Mass Balance: We will not focus on the isotopic disequilibrium terms. Conventional use of isotopes to partition fluxes between Ocean (No) and Land (Nl). However, ever increasing density of observations, especially at terrestrial sites. Allows us to focus on the del_al term. Stomatal conductance control on isotopic variability. Pool size determines discrimination. Stomatal conductance accounts for 120 GTC and approximately 30,000 GT H20 leaving through transpiration. Can we use atmospheric observations to make inferences about stomatal conductance? What physical mechanisms control stomatal conductance on a global scale? And ultimately what limits carbon uptake by the terrestrial biosphere. 18 18 18
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Estimating changes in the global CO2 growth rate
To estimate network error we did a bootstrap reanalysis of the global network of CO2 observations, whereby we simulated 100 networks of 40 sites to estimate the error distribution since 1980. Prior to 1980 we used mean of MLO and SPO 19 19
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Fossil fuel emissions are increasing
but uncertainty is increasing as well Uncertainty Different inventories give different estimates primarily due to slightly different energy to emission conversions. Tax error is pervasive until audited. Emissions are increasing over time, but uncertainty is increasing. 20 20 20
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Land use emission estimates continue to decline
Different inventories use different techniques Houghton-bookeeping Stocker-Land-Use maps CO2 and regrowth Yang-Land-Use maps CO2, N and regrowth All estimates show a slight decline over the last 20 years. 21 21
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Total emission scenarios
Emissions Matrix: FF1 FF2 FF3 FL1 FF1 +FL1 … …. FL2 FL3 FF3 +FL3 Land Use and Fos Fuel emissions were combined in a Monte-Carlo Framework N = 500 X 3 X 3 = 4500 22 22
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Diminished carbon sinks: Is there any observational evidence?
Stomatal conductance For a lack of a better metafor the ‘hockey-stick’ shape is mostly in response to CO2 increase (in the denominator of both models) Net Uptake illustrated with respect to the atmosphere whereby a decrease indicates increased C uptake by the biosphere! 23 23 23
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Earth’s ‘carbon crutch’ continues to grow
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What can we conclude given current information?
Energy and CO2 Emissions in Montana Recent trends in US CO2 emissions Global trends and uncertainties in CO2 emissions An audit of the global C cycle
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