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Global Warming Lecture 3

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Global Warming Lecture 3 A departure from previous years approach. This lecture will provide a case FOR anthropogenic global warming The next will provide a case ... – PowerPoint PPT presentation

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Date added: 8 July 2019
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Title: Global Warming Lecture 3


1
Global WarmingLecture 3
  • A departure from previous years approach.
  • This lecture will provide a case FOR
    anthropogenic global warming
  • The next will provide a case AGAINST
    anthropogenic global warming
  • You job is to decide which elements you believe,
    and importantly WHY?
  • It is not the case that one lecture is correct
    and the other wrong.
  • As these lectures are supposed to represent what
    you might see at a research conference, I will
    not write notes on the board.

2
Outline
  • A link between radiative forcing and temperature
  • Human induced forcing through greenhouse gases is
    real
  • Feedbacks amplify (not damp) the effects
  • The temperature of the earth is rising

3
Climate sensitivity
4
Evidence for Milankovitch theory
(wikipedia!)
5
Px272 Lect 3 Forcing and feedback
Balance of solar incoming, and earth emitted
outgoing radiation (Ssolar const/4)
Increments relative to pre-industrial era
Assumption that solar incoming constant. Change
is made in surface temperature as a consequence
of forcing. i.e.
For a given radiative forcing we get a
temperature change given by
6
Global warming potentials (GWP)
The ratio of the radiative forcing produced over
a timescale of 100 years for 1kg of greenhouse
gas, relative to 1kg of carbon dioxide.
Greenhouse gas GWP
Carbon dioxide (CO2) 1
Methane (CH4) 25
Nitrous Oxide (N20) 298
Hydrofluorocarbons (HFCs) 12-12000
Perfluorocarbons (PFCs) 5000-12000
Sulphur hexafluoride (SF6) 22200
Houghton (2009)
7
Figure TS.5
Anthropogenic Radiative Forcings IPCC AR4 2007
8
Aerosol direct forcingNature 438, 1138 (Dec 2005)
9
Aerosol indirect forcing effect
10
Figure TS.5
Radiative Forcings IPCC AR4 2007
11
G/house gas and aerosol buildup
12
IPCC 2007
13
  • Industrial sulphate aerosols appear to have
    peaked for Greenland record.

14
Response and Feedback
Add in some feedback
f defined as
Feedback can either amplify, or damp the impact
of changes in forcing Positive feedback has
positive f, negative feedback has negative
f. Stability limit flt1 (some would claim this is
exceeded).
15
Response and Feedback
16
Water vapour feedback
Water saturation (mid troposphere) lt-Simulation
Observed-gt
17
Cloud Radiation Feedback
Potentially quite large Altitude dependent Net
highly uncertain
18
Ocean Circulation Feedback
  • Huge heat capacity
  • - delays warming
  • Circulation driven by
  • temperature difference
  • salinity difference
  • rotation of earth
  • redistributes regionallymore winter heat to NW
    Europe from ocean transport than from sun
  • global heat redistribution still dominated by
    atmosphere

19
Ice Albedo Feedback
20
Feedback means that global temperature rises are
twice what is expected for simple models
21
coupled Ocean-Atmosphere General/Global
Circulation Models
100km horizontal resn Finer (2) for ocean
than atmosphere. 20 layers atmosphere 20
layers ocean. Geography inevitably
coarse. Regionalisation redo simulation of
one region only (e.g. Europe) matched onto cruder
global simulation
22
Basic Physics
23
Features and processes
Moist processes Evaporation condensation
clouds and latent heat
Radiation processes, light and IR
Sub-resolution convection -gt effective
viscosity dispersion
Surface changes, e.g. of albedo and roughness
Atmosphere-Surface exchange heat, vapour,
liquid, momentum
24
Turbulence
Sub-resolution convection -gt effective
viscosity dispersion
25
Climate Weather
26
State of art ca 2000
-gt Major volcanic eruptions are a visible and
predictable perturbation on the climate.
27
Figure TS.23
Greenhouse gas forcing has very likely
90 caused most of the observed global warming
over the last 50 years. IPCC 2007
IPC 2007
.likely 67.. IPCC 2001
28
IPCC 2007
Previous predictions correct to show wide
error bars
29
Temperature rise from doubling CO2 (equivalent)
IPCC2007
30
Predictability
  • General claim
  • Weather chaotic (beyond two weeks)
  • but wider/longer scale climate changes
    relatively predicable.

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
Exploit Expensive OAGCM calculations
-gt calibrate simpler climate simulations
-gt mass produce climate predictions for
different future scenarios
31
SpecialReport on Emissions Scenarios
B2
  • Population peaks mid century.
  • A1 technology-led economy,
  • F fossil fuels vs ( B
    balanced ) vs T non-fossil fuelled.

B1 info service economy sustainability
global solns.
  • Population continues to increase.
  • A2 very heterogeneous world (business as
    usual)
  • B2 lower growth rate emphasis on local
    solutions

not predictions, but a range of plausible
assumptions
32
The global climate of the 21st century
IPCC S/PM 2001
33
Figure TS.28
IPCC 2007 Scenario -gt OAGCM -gt Climate
prediction
34
Figure 10.4
IPCC 2007
35
Arctic sea ice decrease
36
(ca 2002)
37
IPCC 2007
38
Observed and projected changes in extreme weather
and climate events.
IPCC S/PM 2001
39
(No Transcript)
40
OAGCM predictions (sample)
annual mean change of the temperature (colour
shading) and its range (isolines) (Unit C)
for SRES A2 and B2 . period 2071 to
2100 relative to 1961 to 1990
B2
IPCC2001
41
Projected temperatures
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