Energy and Climate: from basic physics to intergenerational equity

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Energy and Climate from basic physics to
intergenerational equity

• Myles Allen
• Department of Physics, University of Oxford

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A 110,000-trillion scale model of the problem

• 50g coal represents 0.5trillion tonnes of carbon
  (TtC)
• Burning 0.5TtC and releasing the CO2 causes 1oC
  global warming a Global Warming Unit (GWU).
• We started off with 10 GWU
• 1 GWU already burned since 1750.
• 1 GWU conventional reserves of oil and gas.
• 5 GWU conventional reserves of coal.
• 3 GWU unconventional reserves (tar sands etc.).
• It took us 250 years to use the first GWU. On
  recent projected emission trends it will take
• 35 years to use the next one.
• lt30 years to use the next one.
• lt20 years to use the next one etc.

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Will we burn that carbon?

• 50g coal
• 0.5 MegaJoules (MJ) of electric energy (1.5 MJ of
  heat).
• Energy content of 1kg Li battery, fully charged.
• 50l hydrogen gas at room temperature and
  pressure.
• Output of a 1m2 solar PV panel over 1.5 hours in
  bright sun.
• At 100/bbl, each GWU is worth 350 trillion
• (minus the cost of extraction).
• (5 times current world annual output of goods
  services).
• Will alternative energy sources make GWUs 3 to 10
  economically unattractive before we use them?

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The last time we found an apparently
inexhaustible source of high-density energy
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The implications of 3-4oC global warming
increase in summer temperatures over the next 80
years
IPCC
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To put this in context Summer 2003 temperatures
relative to 2000-2004
From NASAs MODIS - Moderate Resolution Imaging
Spectrometer, courtesy of Reto Stöckli, ETHZ
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Modelling Southern European area-averaged
June-July-August summer temperatures
Future projection
Instrumental observations
Natural drivers only
All drivers included
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Impacts of the 2003 summer heatwave
2003 Summer Heat-wave
Influenza epidemic
Schär Jendritzky, 2004
Daily mortality in Baden-Württemberg, Germany
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Human contribution to the risk of the 2003
heat-wave Stott et al, 2004
Return periods for European heat-waves
9x increase in risk
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And a weather event a little closer to home
Photo Dave Mitchell
South Oxford on January 5th, 2003
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Areas of risk in Oxford
You are here
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Projected changes in winter rainfall over the
next 80 years dots indicate multi-model agreement
IPCC
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The problem in October 2000 and January 2003 a
consistently displaced Atlantic jet-stream
500hPa wind speed Autumn climatology (colours)
Autumn 2000 (contours)
Blackburn Hoskins, 2003
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Exploring the role of human influence on climate
in recent extreme weather events
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Autumn 2000 in the real world (ERA-40
reanalysis)and in one of the wetter
members of our ensemble.
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Risk of floods in the year 2000, with and without
the influence of increased greenhouse gases
2x increase in risk
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Increased drought risk in Tripoli due to
greenhouse warming 1900-2000
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So where is this all going and what can we do
about it?

• Climate change is a probably already having a
  substantial impact on human societies and natural
  ecosystems, and its going to get a lot more
  severe.
• What will it take to avert dangerous climate
  change?

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Key driver of change greenhouse gas levels since
the year 0
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Over the coming century, carbon dioxide emissions
are the main driver of change
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So what should we be doing about it?

• Standard model of climate change policy
• Intergovernmental assessments of the overall net
  cost.
• Technically devised optimal global emission
  rate.
• Negotiated national emission quotas.
• Problems
• Net cost is largely irrelevant and disturbingly
  subjective.
• Annual emission rates are incidental to overall
  damage.
• National quotas dont have a great track record
  (so long, and thanks for all the fish).

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The wrong trousers?
G. Prins S. Rayner, James Martin Institute
(2008)
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Why you can always find an economist to justify
any given net cost of climate change
Growth effect losing 100 hurts more if you are
poor PRTP Pure Rate of Time Preference measure
of impatience or chance of future damage being
irrelevant
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Modeling future climate

• You probably have the impression the only way to
  forecast future climate is with fiendishly
  complicated models run on vast supercomputers.
• This is only partly true.
• It is certainly true if you want to say something
  useful about flood risk in Oxford.
• But it isnt true if you want to get a feel for
  what drives global temperature.

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Your very own climate model

• Put together by Niel Bowerman (Oxford Physics)
  and David White (Technology Assisted Lifelong
  Learning Unit)
• http//tall.conted.ox.ac.uk/testarea/climatechange
  /climate.html

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The model

• Simple mixed-layer/diffusive energy balance
  model
• Revelle accumulation of long-term equilibrium
  CO2
• Slow advection of active CO2 into deep ocean
• Diffusive uptake by mixed layer and biosphere
• C-T feedback linear in ?T above preceding
  century
• Emissions scaled to give correct 1960-2000 CO2.

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The constraints

• Warming attributable to greenhouse gases over the
  20th century.
• Effective ocean-troposphere-land heat capacity
  over 1959-98.
• CO2 airborne fraction over 1960-2000 (uncertain
  due to uncertainty in land-use emissions).
• Contribution of C-T feedback to 2100 airborne
  fraction under A2 scenario (constrain with
  C4MIP).
• Rate of advection of active CO2 into deep ocean
  (constrain with available EMICs).

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Of course, to forecast future climate, you need
to think about what the world will be like in 2100
A2 scenario Population(2100)2 x
Population(2010) GNP(2100)6-7 x
GNP(2010) OilCoal gt Gas gt NuclearBiomass
Red Kyoto-level efforts to reduce emissions to
2100 followed by maximal (3/year) reductions in
22nd century
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And the baseline certainly matters
A1 scenario Population(2100)Population(2010)
GNP(2100)11-14 x GNP(2010) Gas gt
NuclearBiomass gt OilCoal
Red Kyoto-level efforts to reduce emissions to
2100 followed by maximal (3/year) reductions in
22nd century
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In both directions
A1G scenario Population(2100)Population(2010)
GNP(2100)11-14 x GNP(2010) Gas OilCoal
gt NuclearBiomass
Red Kyoto-level efforts to reduce emissions to
2100 followed by maximal (3/year) reductions in
22nd century
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So, Kyoto is not enough (no surprise there), but
what will it take?

• Generate idealized emissions scenarios
• Vary those sliders automatically.
• Vary all the uncertain parameters in the model.
• Compare with observations to give more weight to
  more plausible parameter-combinations.
• Plot the results

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A simple recipe for mitigation scenarios
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Red and orange scenarios all have cumulative
emissions of 1TtC (1EgC)
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Response with best-fit model parameters
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Range of responses to benchmark scenario
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Peak warming is determined by total amount of
carbon released into the atmosphere
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not by emissions in 2050
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How fossil fuel reserves relate to atmospheric
capacity
Past emissions
Conventional oil and gas
Conventional oil, gas and coal
Conventional and unconventional reserves
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Will emission rationing ever be enough?

• Emitting a given total amount of CO2 slower makes
  very little difference to the risk of dangerous
  anthropogenic interference in the climate.
• To stay below 2oC, safe atmospheric capacity is
  1TtC, half of which has already been emitted.
• If we (arbitrarily) divide the atmospheric
  capacity by the current fossil fuel mix, the
  carbon content of
• 15 of conventional oil gas reserves (60GtC)
• 95 of conventional coal reserves (2.3TtC)
• 100 of unconventional reserves (1.8TtC)
• needs to stay out of the atmosphere forever.
• Remember we didnt save the ozone layer by
  rationing deodorant.

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Ensuring we do not exceed the atmospheric
capacity the concept of SaFE carbon

• SaFE carbon
• Sequestered
• at-time-of
• Fossil
• Extraction
• SaFE carbon a supply that ensures we never
  exceed the atmospheric capacity.
• Define SaFE carbon with S(C/C0)a
• S fraction sequestered, including compensation
  for leaks.
• C Cumulative emissions from the time policy is
  adopted.
• C0 Atmospheric capacity at the time policy is
  adopted.
• a positive constant.
• C0 and a define the policy little wriggle-room.

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SaFE carbon pathways for a1, a2 a5
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SaFE carbon futures under two scenarios for total
emissions
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Saving the trillionth tonne

• In the build-up to the next Conference of the
  Parties to the Kyoto Protocol, in Copenhagen in
  December, you will hear a lot of rhetoric about
  cutting GHG emissions 20 by 2020, or 50 by
  2050, etc. etc.
• But how much we cut by a given date is incidental
  to the overall risk of dangerous climate change.
• And theres lots of scope for muddling cuts in
  short-lived greenhouse gases with cuts in CO2.
• What really matters is the total amount of CO2 we
  release whether we burn the trillionth tonne.
• How Oxford could help lets buy the trillionth
  tonne.