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Reducing Uncertainty in Predictions of Climate Change

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Title: Reducing Uncertainty in Predictions of Climate Change


1
Reducing Uncertainty in Predictions of Climate
Change
University of Washington, Program on Climate
Change February 11, 2010
2
The perception of a scientific controversy is
often exaggerated in the media
3
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5
Hero of the movie is a Climatologist!
6
Intergovernmental Panel on Climate Change
  • 2007 IPCC Report
  • Started 2004
  • Completed February 2007
  • 152 Authors
  • 450 contributors
  • 600 expert reviewers
  • 30,000 review comments
  • Contents
  • Summary for Policymakers
  • Technical Summary
  • 11 Chapters
  • Frequently Asked Questions
  • 5000 literature references
  • 1000 pages

7
The IPCC Sequence of Findings
IPCC (1990) The unequivocal detection of the
enhanced greenhouse effect from
observations is not likely for a decade
or more. IPCC (1995) The balance of
evidence (gt50) suggests a discernible
human influence on global climate IPCC (2001)
Most of the warming of the past 50 years is
likely (gt66) to be attributable to human
activities. IPCC (2007)
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9
One of the most important outcomes of your study
could be a clear statement of our present
ignorance -Climate Change Panel Respondent (1978)
Over 97 of climate scientists believe humans
are causing the planet to warm. -EOS, American
Geophysical Union (2009)
10
The World Has Warmed
NASA/GISS
  • Globally averaged, the planet is about 1.5F
    warmer over the past century.

11
Consistent Patterns of Warming
  • Mountain glaciers are retreating
  • Arctic sea ice is decreasing
  • Greenland is melting
  • Snow/permafrost decreasing
  • Sea level is rising
  • Ocean heat content is increasing
  • More intense droughts
  • Atmospheric moisture increasing
  • Heavier rainfall events
  • Increased heat waves
  • Decreased cold spells,

WARMING IS UNEQUIVOCAL
12
The IPCC Sequence of Findings
IPCC (1990) The unequivocal detection of the
enhanced greenhouse effect from
observations is not likely for a decade
or more. IPCC (1995) The balance of
evidence (gt50) suggests a discernible
human influence on global climate IPCC (2001)
Most of the warming of the past 50 years is
likely (gt66) to be attributable to human
activities. IPCC (2007) Warming is
unequivocal, and most of the warming of
the past 50 years is very likely (gt90)
due to increases in greenhouse gases.
13
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15
Where Do We Go From Here? Climate Projections for
the 21st Century
11 F
You are here
3.5 F
16
  • Sources of Uncertainty in Future Projections
  • How much will CO2 (and other man-made GHGs)
    increase from the burning of fossil fuels?
  • How much will the climate warm in response to a
    given increase in CO2?

17
  • Climate Sensitivity
  • The equilibrium change in global mean surface
    temperature that results from a doubling of CO2.

Charney Report (1979)
18
The Greenhouse Effect
Without Greenhouse Effect Global-mean Temperatur
e 0 F With Greenhouse Effect Global-mean
Temperature 60 F
Without Greenhouse Effect Global-mean Temperatur
e 0 F With Doubling of CO2 Global-mean Te
mperature 62 F
  • The Greenhouse Effect is natural.
  • Most important greenhouse gases Water Vapor
    (60) and CO2 (25).
  • Global warming results from an anthropogenic
    enhancement of the GHE.

19
  • Climate Feedback
  • A sequence of interactions that may amplify
    (positive) or dampen (negative) the response of
    the climate to an initial perturbation.
  • Example Snow/Ice Positive Feedback Loop

20
Climate Sensitivity Depends On Feedbacks Water
Vapor
All models predict a strong positive feedback
from water vapor.
21
IPCC Assessments Water Vapor Feedback
1990 The best understood feedback mechanism is
water vapor feedback, and this is intuitively
easy to understand
22
Water Vapor Feedback
Atmospheric Water Vapor (kg/m2)
Satellite observations illustrate how water vapor
enhances regional differences in ocean
temperature.
1.
Ocean Surface Temperature (K)
2.
Greenhouse Effect (W/m2)
3.
1. Warmer oceans ? more water vapor. 2. More
water vapor ? larger Greenhouse Effect. 3. Larger
GHE ? warmer oceans.
23
IPCC Assessments Water Vapor Feedback
1990 The best understood feedback mechanism is
water vapor feedback, and this is intuitively
easy to understand
24
IPCC Assessments Water Vapor Feedback
1990 The best understood feedback mechanism is
water vapor feedback, and this is intuitively
easy to understand 1992 There is no
compelling evidence that water vapor feedback
is anything other than positivealthough there
may be difficulties with upper tropospheric
water vapor
25
IPCC Assessments Water Vapor Feedback
1990 The best understood feedback mechanism is
water vapor feedback, and this is intuitively
easy to understand 1992 There is no
compelling evidence that water vapor feedback
is anything other than positivealthough there
may be difficulties with upper tropospheric
water vapor 1995 Feedback from the
redistribution of water vapor remains a
substantial source of uncertainty in climate
models
26
IPCC Assessments Water Vapor Feedback
1990 The best understood feedback mechanism is
water vapor feedback, and this is intuitively
easy to understand 1992 There is no
compelling evidence that water vapor feedback
is anything other than positivealthough there
may be difficulties with upper tropospheric
water vapor 1995 Feedback from the
redistribution of water vapor remains a
substantial source of uncertainty in climate
models 2001 The balance of evidence favours
a positive clear-sky water vapour feedback of
magnitude comparable to that found in (model)
simulations
27
IPCC Assessments Water Vapor Feedback
1990 The best understood feedback mechanism is
water vapor feedback, and this is intuitively
easy to understand 1992 There is no
compelling evidence that water vapor feedback
is anything other than positivealthough there
may be difficulties with upper tropospheric
water vapor 1995 Feedback from the
redistribution of water vapor remains a
substantial source of uncertainty in climate
models 2001 The balance of evidence favours
a positive clear-sky water vapour feedback of
magnitude comparable to that found in (model)
simulations 2007 Observational and modelling
evidence provide strong support for a combined
water vapour/lapse rate feedback of around the
strength found in GCMs
28
Testing Model Predictions of Water Vapor
Models capture Moistening of tropical
atmosphere during warm (El Nino) events. Drying
of tropical atmosphere during cold (La Nina)
events.
Pinatubo
La Nina (cold)
El Nino (warm)
El Nino
La Nina
29
Global Cooling and Drying after Mt. Pinatubo
Temperature (C)
Water Vapor (mm)
  • Atmosphere cools and dries following eruption.
  • Climate models successfully reproduce observed
  • cooling and drying.

Eruption of Mt. Pinatubo June 1991
30
Testing Water Vapor Feedback
Observed
  • Model without water vapor feedback significantly
    underestimates cooling.
  • Water vapor amplifies pre-existing temperature
    change (either warming or cooling).

31
Climate Sensitivity Depends On Feedbacks Clouds
-

Surface T
Reflected Sunlight
Greenhouse Effect
?
Cloud Cover


Cloud feedback is uncertain in both magnitude and
sign.
32
Cloud Feedback in Models A Case Study
IPCC TAR Models
(2001)
Change in Low Cloud Amount (/K)
33
Cloud Feedback in Models A Case Study
Fall 2003
GFDL
Change in Low Cloud Amount (/K)
2xCO2 Climate Sensitivity (K)
NCAR
34
The Problem CloudsRegional contribution to
intermodel spread in cloud feedback
Subtropical marine stratocumulus clouds are
responsible for most (2/3) of the uncertainty in
cloud feedback in current models.
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37
http//www.atmos.washington.edu/2008Q2/101/student
_cloud_photos/SC_j_reuer.jpg
38
Resolving Uncertainties
  • Improved observations and more sophisticated
    models are important tools to resolving the
    uncertainties in cloud feedback, but ...

Cloud Radar
GFDL Model
39
Cloud Feedback Puzzle
Model Predicted Change in Low Cloud from 2xCO2
Model Simulated Change in Low Cloud From
Observable (ENSO) Variability
?
Change in Low Cloud Amount (/K)
40
Key Climate Feedbacks Current model estimates
of climate feedbacks
Adapted from Gregory et al. (2009)
Negative Positive
Snow/Ice
Water Vapor
Negative Positive
Climate Feedback Strength (W/m2/K)
  • Water vapor provides a strong positive feedback
    in all models.
  • Clouds and the carbon cycle are potentially
    strong, but very uncertain.

41
Climate Feedbacks Interact
Current Model Range
Model Range w/out Water Vapor Feedback
  • The presence of a strong positive feedback from
    water vapor amplifies both the magnitude of
    climate change and the impact of uncertainty in
    other feedbacks.
  • This makes it hard to reduce uncertainty at high
    sensitivities (Roe and Baker 2007)

42
Global Warming is NOT Fair
  • The poorest countries do not contribute
    significantly to the problem - but they will pay
    the greatest cost in adapting to it.

43
Thank you
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