Atmospheric CO2, climate change
and the global carbon cycle
Slides created with the material provided by
prof. Laurent Bopp - Directeur de Recherche au CNRS
Laboratoire de Météorologie Dynamique
Institut Pierre-Simon Laplace
Professeur Attaché à l’Ecole Normale Supérieure
Outline
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Introduction
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The carbon cicle: anthropogenic emissions, sources and sinks
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Coupled climate-carbon evolution in the 21st century
- Conclusions
Introduction
A definition of Climate
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Horizontal zone of the Earth's surface measured by lines parallel to the equator, from Greek klima "region, zone," literally "an inclination, slope," thus "slope of the earth from equator to pole".
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The regular pattern of weather conditions of a particular place (Oxford dictionary)
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The long-term average of weather, typically averaged over a period of 30 years (Wikipedia)
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Climate is what you expect, weather is what you get! (Robert Heinlein)
About Climate
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Complex, non-linear and non-autonomous dynamical system
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Climate has never been static, nor in equilibrium
- Climate has various time-scales, local and global variabiliy
- Hard to separate natural and anthropogenic change
- Main proxy for climate: temperature (but also precipitation, atmospheric/oceanic circulation, ice cover,...)
An example of climate variability
Vostok, Antarctica ice core as reported by Petit et al., 1999.
Higher dust levels are believed to be caused by cold, dry periods.
Actual climate change: an anthropogenic issue?
source: IPCC (2013)
The role of CO2 in the global warming
source: IPCC (2013)
The Keeling Curve
CO2 emissions and the 1.5°C target
The carbon cicle: anthropogenic emissions
Fossil Fuel & Cement CO2 Emissions
Text
source: CDIAC; Le Quéré et al 2018 ; Global Carbon Budget 2018
Fossil Fuel & Cement CO2 Emissions
Text
source: CDIAC; Le Quéré et al 2018 ; Global Carbon Budget 2018
Fossil Fuel & Cement CO2 Emissions
Text
source: CDIAC; Le Quéré et al 2018 ; Global Carbon Budget 2018
Fossil Fuel & Cement CO2 Emissions
Text
source: CDIAC; Le Quéré et al 2018 ; Global Carbon Budget 2018
Global carbon atlas
Text
source: http://www.globalcarbonatlas.org
source: NOAA
CO2 latitude distribution in the atmosphere
2002-2013 (monthly averages)
source: NOAA
Atmospheric CO2 concentration growth rate and emissions
Only half of the antropogenic CO2 emissions stays in the atmosphere
Atmospheric CO2 variation: the role of the carbon sinks
ΔCO2 = Emissions – A_ocean – A_land
Atmospheric CO2 variation: the role of the carbon sinks
source: CDIAC; NOAA-ESRL; Le Quéré et al 2018; Global Carbon Budget 20168
Atmospheric CO2 variation: the role of the carbon sinks
A closed budget: ΔCO2+ΔO2=0
ΔCO2 = Emissions – A_ocean – A_land
ΔO2 = -α. Emissions – β . F_land
Coupled climate-carbon evolution in the 21st century
A Climate – Carbon Coupled System
Indications from the past: glacial cycles
source: Siegenthaler et al., Science 2005
The relationship between CO2 and Antarctic climate remained rather constant over this interval.
Indications from the past: interannual variabilty
source: Wang et al., PNAS 2013
CO2 atmospheric and El Niño
Rate of growth CO2 (PgC/y)
Carbon cycle projections
First step: emission scenarios
Moss et al., 2010
Carbon cycle projections
Second step: climate models
Temperature anomalies
Carbon Stocks
Carbon cycle projections
Second step: climate models
Positive retroaction: the feedback induces an additionnal atm. CO2 of
200 ppm in 2100
Carbon cycle projections
Second step: climate models
Therefore: -soil warming, increasing aridity
-decreasing solubility, increasing stratification
Carbon cycle projections
Second step: climate models
“Warming tends to reduce land and ocean uptake of atmospheric carbon dioxide, increasing the fraction of anthropogenic emissions that remains in the atmosphere.”
But the uncertainties link to the retroaction are high
Temperature (°C)
Feedback analysis
α : Climate sensitivity to CO2 (°C / ppm)
β : Sink sensitivity to CO2 (PgC / ppm)
γ : Sink sensitivity to climate (PgC / °C)
Feedback analysis
Linear analysis
Feedback analysis
The different parameters
-Similar sensitivity to CO2 for the ocean and the terrestrial biosphere
-Negative sensitivity to climate, but stronger for the terrestrial biosphere
-Largest uncertainty for the terrestrial biosphere
Feedback analysis
The different parameters: regionalization
Sensitivity to CO2 (β)
source: IPCC, AR5, 2013
Sensitivity to climate (γ)
Feedback analysis
The different parameters: Ocean and CO2
- High values for the North Atl. / Southern Ocean – agreement among
different models
- Consistent with the estimates done for the carbon absorpion for the
present times (Mikaloff-Fletcher et al. Gruber et al.)
Sensitivity to CO2 (β)
Feedback analysis
The different parameters: Ocean and Climate
- Positive and negative values! - Little agreement among the models
- Negative: decreasing of solubility, stratification...
Positive: melting sea ice, mixing more important
Sensitivity to climate (γ)
Conclusions
Some conclusions
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Climate Projections: predicting the future evolution of carbon sinks is crucial. This requires to study economy-ecology-climate coupling.
- All models projcect a positive feedback between climate & the carbon cycle, but with large uncertainties
Cumulative anthropogenic CO2 emissions since 1870
Temperature variation from averages 1861-80 (°C)
Emissions vs Warming
< 2°C only if the cumulative emissions will stay below 2900 PgCO2
Emissions vs Warming
In order to limit the global warming to 2°C, the emissions must be reduced of 40-70% by 2050 (vs. 2010) and 100% by 2100
Carbon cycle: non-equilibrium system in any time scale
Caveat
- Correlation does not implies causations
- Mathematics and physics foundations of climate are still not completely understood
- Understanding climate is a worth scientific challenge
- Human beings [are forced to] take decisions during their life with much higher uncertainty than we have on anthropogenic contributions to climate change (prof. Micheal Ghil, UCLA and ENS)