Introduction to Earth System Science

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Introduction to Earth System Science
Andy Pitman Climate Change Research Center The
University of New South Wales a.pitman_at_unsw.edu.au
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The Earth System

• Everything

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Last 600,000 years
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The Earth System

• Everything
• Everything that matters

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Last 1200 years
These are variants on the hockey-stick note
you would reach identical Conclusions that the
Earth is warming from each stick
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The Earth System

• Everything
• Everything that matters
• Everything that matters to your personal interest

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Last 300 years
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The Earth System

• Everything
• Everything that matters
• Everything that matters to your personal interest
• Define matters
• Contextualize personal interest

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Key messages

• Your problem may be directly relevant to others
  interests but
• Your problem may not be relevant to others
  interests
• Be very careful what you claim !
• Proving X matters for issue Y does not mean it
  matters for problem Z
• Problem Z may be resolvable without your
  contribution

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 Schematic diagram of various components and
interactions of the climate system.  
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Climate Modelling
Governing equations
Forcing conditions
Initial conditions
Model output
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Three-Dimensional Climate Models (GCM)
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Earth System Modelling

• There are no governing equations, like those for
  the biophysical system that control
• Human behaviour
• Social systems
• Economics
• Emergence of heros
• So coupling these into ESMs is difficult

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ESMs

• ESMs are not better climate models
• ESMs cannot be achieved via evolution of CSMs
• But we need evolution of CSMs to deal with AR5,
  AR6
• And we need a revolution to create genuine ESMs

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Key message

• The climate system ? the earth system
• I think of the Earth System as the integrated
  climate and human systems
• I work as if humans are a forcing
• Humans are not a mere forcing they are part
  of the feedback system
• I will focus on Climate System Science from here
  

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Climate model components

• So, what is in a climate model?
• Atmosphere
• Ocean
• Sea ice
• Terrestrial surface

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Ocean GCM
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Sea ice models
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Land surface models
?1
?2
?3
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carbon and nitrogen
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Emission scenarios

• Past emissions are trivial use observations

 Atmospheric carbon dioxide concentrations from
1744 to 1992. The increase in carbon dioxide
concentration in the atmosphere is roughly
exponential.
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The Past and the Future

• Instrumental Data
• Proxy Reconstructions
• Model Simulations

?T
0.4
0.2
0
-0.2
-0.4
-0.6
-0.8
1000
2000
1500
500
Year
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Temperature

• Continued greenhouse gas emissions at or above
  current rates would cause further warming - very
  likely larger than those observed during the 20th
  century.

2008
2007
2006
2005
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Why ESMs

• There are two fundamental reasons for ESMs
  emerging
• Human-climate interactions
• Abrupt climate change

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Abrupt climate change

• The nonlinearity of the climate system may lead
  to abrupt climate change
• The term abrupt refers to time scales faster than
  the typical time scale of the responsible forcing
  
• not all abrupt climate changes need be externally
  forced.

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Abrupt climate change
.

• Some possible abrupt events include
• collapse of the thermohaline circulation,
• Ice sheet and/or glacial collapse
• Massive melting of permafrost
• increases in soil respiration
• Large-scale ecosystem die back
• Triggered by thresholds or tipping points

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What causes abrupt changes?

• Thresholds
• Net terrestrial carbon balance
• Forest cover

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Thresholds
Models do not agree
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Threshold exceeded related to loss of
competitiveness of trees in a slowly drying
climate Does not include fire
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• What are the risks of abrupt climate change in
  the next 10, 20, 50, 100 years
• ?
• IPCC (2007) suggest no evidence that it can occur
  this century
• Recent evidence in the Arctic, Antarctic and THC
  behaviour suggests that it could

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Probability and avoidance

• Two approaches
• Ask experts to judge the likelihood of a change
  occurring Krergler et al., 2009
• Ask how much warming is likely and then what
  would this mean Ramanathan and Fung, 2008

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How much warming ?

• probabilistic range from 1.4oC to higher
• values values gt 8 are likely inconsistent
  with theory

Lets say 4oC by 2100
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Expert judgement

• Ask a suite of experts
• What is the likelihood of
• Collapse of the THC
• melt of Greenland ice sheet
• Collapse of the west Antarctic ice sheet
• Die back of the Amazon
• More persistent El Nino

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Die back of the Amazon

60 probability 30 - 100
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Thresholds
Models do not agree
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But problem solved
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Conclusions

• Likelihood of abrupt climate change in the future
  depends on
• Amount of greenhouse gases
• Very uncertain
• Rate of increase in greenhouse gases
• Poorly known
• How much temperature changes regionally
• Poorly known

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Conclusions

• Likelihood of abrupt climate change in the future
  
• Is really unknown
• Modeling efforts and expert analyses contributing
  to this area
• Very much an emerging field
• Critically needs an earth systems approach. You
  cannot capture probabilities in a climate system
  model

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Conclusions

• Climate system models include sub-models of the
• atmosphere,
• oceans,
• cryosphere,
• terrestrial surface
• And the flows of energy, mass, biogeochemicals
  etc
• All coupled in the form of computer code.

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Conclusions

• earth system models include sub-models of the
• atmosphere,
• oceans,
• cryosphere,
• terrestrial surface
• And the flows of energy, mass, biogeochemicals
  etc
• And human systems (economy, society )

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Conclusions

• Need to develop climate system models via
  evolutionary steps
• Need a revolution to develop genuine earth system
  models with human systems (economy, society )
• Real need and urgent need to do both

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The Earth System

• Earth System Science views the Earth as a fully
  coupled system
• You need an Earth Systems approach to understand
  the Earth System .
• But

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The Earth System

• Its the economy stupid !!!
• ESS is important where it contributes to
  solutions
• To problems that matter to those that fund us