Demystifying global warming

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Demystifying global warming

• Some basic observations for international
  students
• JN Birchall

Global Warming Update,
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• The greenhouse effect
• Making predictions and some possible surprises
• What are the predictions?
• Past trends in climate
• Debates on the climate change problem
• Policy advice
• Supplementary materials
• Exercise on observations of recent climate change
• Information sources and ideas

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The greenhouse effect
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(No Transcript)
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More gas!
Concentrations of greenhouse gases are higher now
than at any time for the past 500,000 years
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Making predictions

• How are predictions made?
• What are the sources of uncertainty?
• Can we trust climate models?
• What factors do models include?
• Are there major sources of uncertainty not
  accounted for?

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Basis of climate change predictions
Uncertainty
Socio-economic scenarios
V. large
Greenhouse gas emissions
Large
Greenhouse gas concentrations
Moderate
Moderate
Predicted temperature change
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CO2 in SRES scenarios (SRES, 2000)
IPCC 2001 http//www.grida.no/climate/ipcc_tar/wg1
/figspm-5.htm
Activity Explore the IPCC scenarios and discuss
their relative likelihood and/or policies which
would see them fulfilled
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GCM structure
Climate Research Unit, UEA
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One way to test a climate model Comparing
observed climate with modeled climate
IPCC (2001) Figure 8.2 lower left
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Major change to predictions from similar GHG
scenarios (1996 cf. 1990)
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Some possible surprises.

• Methane hydrates (oceans 9500 Gt, permafrost 400
  Gt)
• Carbon cycle strength of ocean and terrestrial
  sinks
• Ocean circulation the thermohaline conveyor

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Methane hydrates stored in oceans and permafrost
Activity If 10 of methane hydrates were
released, how does this compare with
anthropogenic sources?
NASA Earth Observatory http//earthobservatory.nas
a.gov/Newsroom/NasaNews/2001/200112106303.html
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Will natural sinks persist? Activity Evaluate
the impact of the decrease/loss of the oceanic
and/or terrestrial carbon sink on global carbon
flux
Woods Hole research Center (2004)
http//www.whrc.org/carbon/missingc.htm
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Likelihood of decline in MOC - from a survey of
scientists in the RAPID programme http//www.soc.s
oton.ac.uk/rapid/sci/pdf/ann_mtg_survey.pdf
Temperature change following shutdown of the
North Atlantic conveyor (Vellinga and Wood, 2002.
Climatic Change 54 251-267)
Activity To what extent should adaptation policy
be formed by the possibility of North Atlantic
conveyor shutdown?
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What are the predictions?

• Range
• Regional patterns

• Changing ideas
• Seasonality

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IPCC(2001) Fig 9.14
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IPCC (2001) Fig 9.10d. Multimodel ensemble annual
temperature change 2071-2100 - 1961-1990 Shading
- temp change, Blue lines - range oC, green -
mean change/mean sd
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IPCC (2001) Fig 9.11d. Multimodel ensemble annual
precipitation change 2071-2100 -
1961-1990 Shading - mean change, red lines -
range, green - mean change/mean sd
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IPCC reports- evolving predictions of climate
change

• Year Global temp Sea level
• rise oC rise cm
• 1990 3.0 (1.5-4.5) 65
• 1995 2.0 (1.0-3.5) 48 (13-94)
• 2001 1.4-5.8 9-88
• No best guesses

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Seasonality can be more important than net
change - e.g. UK precipitation (UKCIP02)
www.ukcip.org.uk
2020s
2050s
2080s
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Past trends in climate

• Is there a trend in global climate change?
• How do current temperatures compare with those in
  the past?

How much has global temperature risen over the
past 100 years?
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Timing of IPCC report preparation
2000
Activity(s) Are current trends in climate
consistent with predictions for the future? See
file.
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Global temperature reconstructions for last 1000
years are we now outside the range of natural
variability?
no
probably yes
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Is the hockey stick still valid?

• Multiple spaghetti curves now published
• larger changes than original hockey stick
• still show the late C20th as the warmest period
  of the last millennium
• how critical is this anyway to the case for
  human-induced warming?

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DEBATES

• There is genuine broad (although not 100)
  consensus in the climate science community on
  main issues
• Argument, scepticism and hypothesis testing are
  at the heart of good science
• Publication of research, review and quality
  control are essential in this process

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Arguments of climate sceptics

• Trends. There is no significant trend in global
  temperature (e.g. urban heat island effect,
  geographic coverage of data)
• Attribution. Human activities are not responsible
  for observed trends
• Impacts. The negative impacts of predicted
  climate change are over-estimated cost-benefit
  analysis does not support mitigation action

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Trendse.g. Urban heat island
Activity Compare temperature records from urban
and rural areas in the UK is there a systematic
difference and how big is it?
Sources http//antwrp.gsfc.nasa.gov/apod/ap040822
.html http//data.giss.nasa.gov/gistemp/2005/
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Attribution

• Observed changes are
• within natural variability
• due to other effects (e.g. solar variability)

IPCC (2001) Figure 4 from SPM. Model outputs
using natural (solar, volcanic) and anthropogenic
(GHGs, aerosols) climate forcing
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Impacts sceptics
The costs of mitigating climate change are
greater than the benefits gained from adapting to
change Best exemplified by Bjorn Lomborg in the
skeptical environmentalist
Activities How accurate are estimates of costs
and benefits likely to be? Economic costing does
not include costs to natural systems does this
matter?
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Science, consensus and debate
Consensus
Sceptic
Supporter
Contrasting reading - Fact vs fiction? Is the
distinction clear?
Activity Take extracts from the above (or use
www sites) and identify differences in style,
language, use of documentation, nature of
documentation
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International policy is scientific advice
followed?
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International policy
Scientific advice
Pressure groups ()
Media and public opinion
Government delegates
International policy
Acceptance in national governments
Government policy .. and action
Activity Follow one of the COP meetings linked
to the UN Framework Convention on Climate Change
www.unfccc.org
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What are desirable levels of future climate
change?

• Defined by
• Global temperature (2oC?)
• Global emissions (2.5 Gt C fossil fuels pa?)
• Atmospheric concentration (450-550 ppm CO2?)
• Timescale
• e.g. UK RCEP (2002) Suggest 60 reduction on 1990
  CO2 emissions by 2050 for UK
• Compare with
• Kyoto target of c. 5.2 by 2008-2012 for Annex 1
  countries
• UK Government target of 20 by 2010 (and may hit
  10....)

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Use the graph below from the RCEP Energy report
as a starting point for debating questions such
as Which parts of the world are the biggest
contributors to climate change? Should targets
for reductions be based on current total
contributions, per capita emissions or perhaps
emissions per GDP?