Transcript GGP3015 CLIMATIC CHANGE: Recent and future

Demystifying global
warming
Some basic observations for
international students
JN Birchall
‘Global Warming Update’,
• 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
The greenhouse effect
381
More gas!
‘Natural’ CO2 conc.
Concentrations of
greenhouse gases
are higher now
than at any time
for the past
500,000 years
Making predictions
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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?
Basis of climate change predictions
Uncertainty
V. large
Socio-economic scenarios
Large
Greenhouse gas emissions
Moderate
Greenhouse gas concentrations
Moderate
Predicted temperature change
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
GCM structure
Climate Research Unit, UEA
One way to test a climate model: Comparing
observed climate with modeled climate
IPCC (2001): Figure 8.2 lower left
Major change to
predictions from
similar GHG
scenarios
(1996 cf. 1990)
Some possible surprises….
• Methane hydrates (oceans 9500 Gt,
permafrost 400 Gt)
• Carbon cycle: strength of ocean and
terrestrial ‘sinks’
• Ocean circulation: the ‘thermohaline
conveyor’
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.nasa.gov/Newsroom/NasaNews/2001
/200112106303.html
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
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?
Likelihood of decline in
MOC - from a survey of
scientists in the RAPID
programme
http://www.soc.soton.ac.uk/rapi
d/sci/pdf/ann_mtg_survey.pdf
What are the predictions?
• Range
• Regional patterns
• Changing ideas
• Seasonality
IPCC(2001) Fig 9.14
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
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
IPCC reports
- evolving predictions of climate change
Year
1990
Global temp
rise oC
3.0 (1.5-4.5)
Sea level
rise cm
65
1995
2.0 (1.0-3.5)
48 (13-94)
2001
1.4-5.8
No best guesses
9-88
Seasonality can be more important than net change
- e.g. UK precipitation (UKCIP02) www.ukcip.org.uk
2020s
2050s
2080s
Past trends in climate
• Is there a trend in
global climate
change?
• How do current
temperatures
compare with
those in the past?
Frost fair on the River
Thames (1814)
How much has global temperature risen
over the past 100 years?
Timing of IPCC report preparation
1994
2000
1989
Activity(s): Are current trends in climate consistent with
predictions for the future? See file.
Global temperature reconstructions for last 1000 years: are
we now outside the range of “natural” variability?
1st IPCC report (1990)
“no”
3rd IPCC report (2001)
based partly on using
multi-proxy
palaeoclimate data - the
“hockey-stick” curve
probably “yes”
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?
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
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 overestimated; cost-benefit analysis does not
support mitigation action
Trends
e.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/
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
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?
Science, consensus and debate
Supporter
Consensus
Sceptic
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
International policy – is scientific
advice followed?
International policy
Scientific advice
Media and public opinion
Pressure groups (±)
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
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%....)
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?