Transcript Power Point Overview of Global Climate Change

IPCC Climate Change Report
Moving Towards Consensus
Based on real world data
IPCC Consensus process is
Conservative by Nature
IPCC Consensus Evolution
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FAR: 1990: The unequivocal
detection of the enhanced
greenhouse gas effect from
observations is not likely for a
decade or more
SAR: 1995: The balance of evidence
suggestions a discernible human
influence on global climate
Getting Stronger
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TAR: 2001: There is new and stronger
evidence that most of the warming
observed over the last 50 years is
attributable to human activities
AT4: 2007: Most of the observed increase
in globally averaged temperatures since
the mid-20th century is very likely due to
the increase in anthropogenic greenhouse
gas concentrations.
Climate Modeling Evolution
Better Grid Resolution
Basic Approach
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Coefficient of doubling CO2
Leads to CO2 Stabilization
Scenarios
Basic Future Predictions
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A 2°C rise from today's temperatures
produces 30% species extinction
A 3°C warming will lead to widespread
coral deaths
Water availability in the moist tropics and
in the high latitudes will increase, but will
drop in the semi-arid low latitudes
A 1°C warming will decrease agricultural
yields in the low-latitudes; 2°C increases
yields at high latitudes
Equilibrium Temperature
 Planet radiates as a blackbody in TE with
incoming solar radiation:
A = Albedo; L = 1370 watts per sq meter
T = 278(1-A)4
T = 255K for A=0.32
This is not the right answer compared to
observations
The Role of the Atmosphere
Fo = incident flux
Ts = transmission % incoming
Tt = transmission % outgoing
Fg = Flux from ground
Fa = Flux from the atmosphere.
Fo = Fa + TtFg top of atmosphere equilibrium
Fg = Fa + TsFo outgoing ground equilibrium
F g = Fo
Let Fa = Fo –TtFg
An Inconvenient Coincidence
Preponderance of Evidence
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Want to find indicators of climate change
Requires a) a robust definition and measure of
what constitutes climate and b) an instrumental
precision sufficient to measure change
No one indicator (e.g. smoking gun) exists;
aggregate of all data then forms the
preponderance
Global mean temperature
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Contamination and data reliability/correction
problems render this approach the least
convincing
This is reflected in the relatively large error bars
on overall amplitude of warming
Consensus in Data Sets
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But different analyses use different sets of
thermometers and different selection criteria
Statistical agreement is good
Recent Trends Compared to earlier
assessments
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Shows the effect of including more of the
physics
Expected higher latitude signal
clearly seen
Reinforced with 2D Representation
Winter Signal is Strongest
Both a Surface and Tropospheric
(1-3 km) effect
Central Europe Summer Signal
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Huge statistical signal via baseline/area
test
Record Events depend on wave
form evolution
Global Dimming?
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A potential competeting affect that has
masked the true signal
Results mostly from global aerosal injection
and increase of short wave length scattering
surfaces
Convolution of rayleigh/mie scattering mix is
poorly understood
Volcanic eruptions are also important
Volcanic Eruptions
Global Aresols
 Mostly Industrial; African Source is pyrogenic
and biogenic in nature (drought related)
Convolution of positive and negative
forcings are what we observe.
 GHG produces the net positive here
And all is superimposed on El Nino
Cycle
Putting it altogether
Other indicators
 Sea Ice
 Glacial retreats and glacial mass balance
 Permafrost
 Droughts
 Water vapor feedback
 Cloud cover
 Ocean wave heights
 Sea surface temperature anamolies
Sea Ice – opening of the NW Passage
2007
2006
Glacial Retreat and Mass Balance
1941 - 2005
Wholesale Change in Mass Balance
Permafrost indicators
Summary of the Cyrosphere (frozen land)
observations
Droughts
Water vapor increases?
Cloud Cover
 Extremely difficult to really measure with any
accuracy
 Extant data are inconclusive and noisy
Wave height data shows something!
Ocean Sea Surface Temperature Response
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Its important to realize that virtually all of the
extra (heat) flux goes into the oceans
Big reservoir of heat
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0.1 degree C increase transferred (instantly)
to the atmosphere produces 100 degree C
increase.
Ocean circulation and redistribution of excess
heat is (fortunately) a slow process
But that is where the “pipeline” warming is
even if CO2 was stablized today!
Sea Level Rising
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Sea Level measured at San Francisco
Known SST oscillations increasing in
amplitude
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North Atlantic Oscillation (notice the post
1995 slope):
Future predictions remain uncertain
Physics of Atmospheric Energy Transport
is difficult
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Potential energy
Internal energy
Kinetic energy
Latent heat
Latitude dependent; vertical dependence
Complete Feedback Models too
Difficult to reliably construct
Source of Uncertainties
 Roles of clouds and aerosols in radiative
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transfer models? (e.g. scattering!)
Role of tropical convection and the water vapor
feedback loop?
How well do observations constrain the input
climate parameters?
How to weight the inputs for best fit statistical
model?
Contributions of other greenhouse gases
specifically methane from permafrost release
Global Warming Potential
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TH = Time Horizon (20 or 100 years)
Ax = increased forcing from X (Watts m^2 kg)
x(t) = decay following some hypothetical
instantaneous release of X
Denominator is relevant quantities for CO2
Nominal value for Methane is 21
Do Tipping Points Exist in Climate?
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Does the system have critical phenomena?
Or do the
various and
somewhat
unknown
feedback
mechanisms
serve to
counter this?
The Next Level of Physics in Climate
Science
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More strongly incorporates the role of various
feedbacks particularly water vapor
Identifying critical points (or lack thereof) is
essential in future models
Improved modeling of aerosols and their
scattering properties
Improved modeling of tropical convection to
better understand ocean/atmosphere heat
exchange