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

• Introduction
   
• The carbon cicle: anthropogenic emissions, sources and sinks
   
• Coupled climate-carbon evolution in the 21st century
   
• Conclusions

Introduction

A definition of Climate

• 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".
   
• The regular pattern of weather conditions of a particular place (Oxford dictionary)
   
• The long-term average of weather, typically averaged over a period of 30 years (Wikipedia)
   
• Climate is what you expect, weather is what you get! (Robert Heinlein)
   

About Climate

•  Complex, non-linear and non-autonomous dynamical system
   
• 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

https://scripps.ucsd.edu/programs/keelingcurve/

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

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

Carbon cycle projections

Second step: climate models

But the uncertainties link to the retroaction are high
 

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.)

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

Conclusions

Some conclusions

• 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

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)

Thanks for your attention!