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.

Evidence of Warming

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

More complete radiation balance

1370 / 4

3. Infra-red emission spectrum (over sunny mediterranean)

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

Figure TS.5

Anthropogenic Radiative ForcingsIPCC AR4 2007

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).

(ca 2002)

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

World emissions trends: growth vs mitigation commmitment

UK CO2 emissions

“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

Geological storage of carbon dioxide

736 Gt in North Sea alone (DTI)

Cost-benefit analysis

Discounting

Payback

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.