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PX272 revision summaryTHE UNIVERSITY OF WARWICK Second Year Examinations: Summer 2006 Physics Paper 7 GLOBAL WARMING Answer TWO questions. Time allowed: 1 hour Read carefully the instructions …. A maximum of 25 credit marks will be awarded for each question…. Calculators may be used for this examination.
The following information may be used:
Stefan-Boltzmann Constant 8 -2 -46 10 Wm K
Main topics:
•Evidence of Warming•Atmospheric Greenhouse effect•Forcing and Feedbacks•Scenarios and Modelling•Consequences of Warming•Political Actions•Mitigation Options
Key Revision material:
•J Horton Review article•Assignments + f/back , particularly 2-5•Powerpoint slides on web
Key figures:
•Included here;•Expected to be able to interpret them.
Long term orbital “Milankovich” cycles
NorthernSouthern summer
in northSouthern winter
Seasons now
& TILT oscillation ~41k years & ECCENTRICITY oscillation ~100 k years
Science 2007 (DOI: 10.1126/science.1136843)
Sea level rise particularly underpredicted(note measurement change at 1993: tide gauges -> satellite data)
Atmospheric Greenhouse effect
2 2 4(1 ) 4 eR S A R T
-2
Solar constant at earth orbit:
1370 Wm
Albedo (visble) 0.3 (clouds)
S
A
1. Global Energy Balance
,
Lower Stratosphere
220 50
Effective blackbody temperature
250 20
Mean Surface Temperature
280 10
stratosphere
eff measured
Surface
T K C
T K C
T K C
2. Key Temperatures
4. Troposphere and Stratosphere
: heated from below:
convection dominates heat transport;
radiation not balanced;
profile close to adiabatic limit .
Evaporation/conden
p
Troposphere
dT dpc R
T p
sation of boosts effective ,
profile more shallow than dry air.
: partially heated from above:
Ozone absorbs incoming UV:
stable radiation balance pro
pc
Stratosphere
file, no convection.
: Boundary between T and S sharp,
but shifts with night and day and season.
Tropopause CalculatedRadiation-Convection temperature profiles
SURFACE WARMING
STRATOSPHERE COOLING
SPACE
EARTH
Greenhouse effect
strengthens as earth warms
(feedback)
1960 2000
rise to restore balance with space
larger surface rise results
Response and Feedback
3
3
-23 8 -2 -4 3
3
4
Response of system:
11
4
1 1 0.3 K/(Wm )
4 4(6 10 Wm K )(255 K)
1 harder to estimate and certainly significant
4Feedbacks
S i
is
e Sie
e
s
i
e
F
TT FT
T
T
F
T T
FT
.
Stability limit 1 ?exceeded ... Lovelock 2006
Four key climate feedbacks:
- water vapour 0.5
- clouds (probably negative)
- ocean circulation (mainly retardation + redistribution)
- ice albedo (clea
rly positive)
Ocean Circulation Feedback
Huge heat capacity
- delays warming
Circulation driven by:temperature differencesalinity differencerotation of earth
- redistributes regionally:more winter heat to NW Europe from ocean transport than from sun
- global heat redistribution still dominated by atmosphere
Biological Feedbacks
Negative λ:
some plants grow better at increased CO2 levels, causing an increase in the amount absorbed
Positive λ:
Increased temperature
increased respiration rates (especially for microbes in soil), hence increased CO2 output.
climate stress reduced tree growth and die-back.
Modelling: Basic Physics …
Conservation of fluid momentum:
Navier-Stokes eqns (-> fluids modules) in rotating frame (Coriolis effects)
Vertically: acceln negligible & balance forces;
Conservation of material:
air, water
salinity
Thermodynamics (conservation of energy);
Equation of State: (pressure, temperature,
salinity(ocean), water vapour(atmosphere))
Evidence: Correlation of ice ages with Milankovitch cycles (of earth orbit) Successful replication of response to largest sudden terrestrial perturbations: Volcanoes El Nino changes in ocean circulation Replication of 20th climate trends
PredictabilityGeneral claim: Weather chaotic (beyond ~two weeks) but wider/longer scale climate
changes relatively predicable.
Exploit:
Expensive AOGCM calculations
-> calibrate simpler simulations
-> mass produce climate predictions for different future scenarios
Special Report on Emissions Scenarios
1. Population peaks mid century.A1: technology-led economy,
F fossil fuels vs ( B “balanced” ) vs T non-fossil fuelled.
a range of plausible assumptions
2. Population continues to increase. A2: very heterogeneous world
(“business as usual”) B2: lower growth rate; emphasis on local
solutions (smart but laissez-faire)
B1: info & service economy; sustainability & global sol’ns.
B2
Climate modelling
B2
Climate Prediction
EU target
Consequences of Warming (see assignment 5)
Sea level rise• 0.5-1m to 2100, majority thermal expansion, much already inevitable• Greenland ice 7m now seriously possible, but ~1000 yrs.• W Antarctic 6m, presumed 100’s of years; (?2008: faster?)
(E Antarctica 60m but thought stable)Coastal (especially delta) populations directly vulnerable; loss of coastal
wetland threatens fish breeding etc.
Climate more extreme
• Increased global precipitation but more uneven by time (e.g. fewer moist days) and space (dry get drier, wet get wetter).
• More drought AND more flood
• More and stronger storms (atmosphere as stronger heat engine)
Shift of agricultural productivity
• High northern latitudes gain, tropics lose.
Possible Atlantic Thermohaline shut-off
• NW Europe would lose its major winter heat source (>sun).
Political Actions
1988: Intergovernmental Panel on Climate Change
Assessment reports 1990 1997 2001 2007
1992: Framework Convention on Climate Change (FCCC),signed by over 160 countries , UN conf Rio 1992, effective 1994.
1997: Kyoto Protocol (legislation under the FCCC)first target: average emissions 2008–2012 below 1990 levels by 5- 8%flexibility: Joint Implementation (cheapest savings) Clean Development Mechanism (avert new emissions) Emissions Trading
2005Ratification threshold of KP achieved by Russia ratifying, but NOT the USA or Australia.Europe: emissions trading at ~ €25 / tCO2 ~ €100 / tC .Outside Kyoto: “Asia-Pacific 6” Australia, India, Japan, PR China, S Korea, USA.
2006UK publishes emission reductions legally binding in domestic law
“Avoiding Dangerous Climate Change” CUP 2006
One “wedge”:
reduce the carbon emission rate in 2055by about 1 GtC/year,
Mitigation options:Wedges
Leading wedges (one 2006 opinion)Already happenning?
More efficient vehicles
Less vehicle use
More efficient buildings
More efficient power plants
Replace coal by gas
Technically feasible?
CO2 capture at power station
CO2 capture at H2 plant
CO2 capture at coalsynfuels plant
Nuclear power
Wind power
Societally Challenging on the scale required?
Photovoltaic base power
Wind H2 cars
Biomass fuel
Reverse forest loss
Conservation soil management
PX272 revision summaryMain topics:
•Evidence of Warming•Atmospheric Greenhouse effect•Forcing and Feedbacks•Scenarios and Modelling•Consequences of Warming•Political Actions•Mitigation Options
Key Revision material:
•J Horton Review article•Assignments + f/back, particularly 2-5•Powerpoint slides on web
Key figures:
•Included here;•Expected to be able to interpret them.