Download Climate change science

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Climate Change Science
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Prepared for Westar Business Meeting
Sept. 21-23, 2005
by
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Jay Gulledge, Ph.D.
Senior Research Fellow
Pew Center on Global Climate Change
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State of the science
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• The earth is warming (unequivocal)…
• …at an unprecedented rate (high confidence)
• Effects of warming are being observed now
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(clear observations): Arctic melting, Sea-level rise,
Desertification, altered precipitation, etc.
• Greenhouse gases are increasing due to
human activities (unequivocal)
• Warming of past several decades is largely
caused by human activities (high confidence)
• Warming will continue for a long time in the
future (high confidence)
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Building the Scientific Consensus
• 1990; First Assessment Report of the IPCC
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“The unequivocal detection of the enhanced greenhouse effect from
observations is not likely for a decade or more.”
• 1995; Second Assessment Report of the IPCC
“The balance of evidence suggests a discernable human influence on the
global climate.”
+ • 2001; Third Assessment Report of the IPCC (confirmed by NAS)
“There is new and stronger evidence that most of the warming observed
over the last 50 years is attributable to human activities.”
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• 2005; Joint [11] Science Academies’ Statement: Global Response to
Climate Change
– The scientific understanding of climate change is now sufficiently clear
to justify nations taking prompt action.
– a lack of full scientific certainty about some aspects of climate change
is not a reason for delaying an immediate response…
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Building the Scientific Consensus
• Scientists were not always certain about global warming
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and human-induced climate change.
• Their willingness to draw conclusions about it increased
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gradually, only as evidence mounted over three decades.
• Scientists are naturally skeptical; they have consistently
underestimated rate and magnitude of projected change.
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• It is only with years of examination, reexamination,
synthesis, and debate that scientists reach consensus.
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• The consensus on climate change is now solid.
+ • The remaining uncertainties do not weaken the consensus
because they are relatively insignificant.
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The Scientific Framework
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• How do we know we can trust the science?
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• Studying complex systems, like the climate,
requires a strong scientific framework
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• Individual studies or data sets can be nitpicked.
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• But a multi-faceted framework underpinned
by sound theory holds withstands scrutiny of
a few individual parts.
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ON
TI
VA )
ER ata
BS (d
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constructed from
complementary
components that
together make
up the scientific
method.
O
+ • The framework is
hy T H
si E
ca O
l p RY
rin
cip
le
s)
The Scientific Framework
(p
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UNDERSTANDING
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• Omitting any of the
+ components results
in weak science.
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RECONCILIATION
(data correction
& modeling)
The Scientific Framework
+ • A hole is not
necessarily
fatal – minor
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adjustments
might fill it.
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ON
TI
VA )
ER ata
BS (d
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can withstand a
few small holes.
O
+ • A good framework
(p
ys T H
ica EO
lp R
rin Y
ci p
le
s)
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UNDERSTANDING
RECONCILIATION
(data correction
& modeling)
The Scientific Framework
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TH
rs E
tp O
rin RY
cip
les
)
ON
TI
VA )
ER ata
BS (d
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start appearing
and can’t be
fixed does the
framework
fall apart.
O
+ • Only if lots of hole
(f i
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UNDERSTANDING
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• This usually happens
when the theory is
+ wrong.
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RECONCILIATION
(data correction
& modeling)
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THEORY: Enhanced Greenhouse Effect
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•Heat-trapping gases in
atmosphere make Earth
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habitable
+• A natural phenomenon but
amplified by human activity
(greenhouse gas emissions)
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• Too much of a good thing!
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Scientific Framework for Global Warming
• THEORY (first principles)
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– Human-enhanced greenhouse predicts:
• Rise in greenhouse gas (GHG) concentrations
• Surface warming unique to age of industrialization
• Atmospheric amplification of surface warming
• Planetary energy imbalance (more in than out)
• OBSERVATION (detection using data)
– Surface & atmospheric temperature measurements
– Driver measurements (solar, volcanic, GHG, SO4, etc.)
• RECONCILIATION (data correction & attribution)
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– Removal of systematic bias from data sets
– Physics-based modeling to see if data support theory
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OBSERVATION
• A rise in greenhouse gases began with the industrial age.
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Source: IPCC
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OBSERVATION & RECONCILIATION
CO2 Concentration in Ice Core Samples and
Projections for Next 100 Years
BAU projection
700
Projected
(2100)
650
600
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Projected
BAU human
contribution
by 2100
550
500
450
400
Current concentration
Current
(2001)
350
Human contribution so far
300
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250
200
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150
400,000
300,000
200,000
Years Before Present
(B.P. -- 1950)
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100,000
0
CO2 Concentration (ppmv)
Vostok Record
IPCC IS92a Scenario
Law Dome Record
Mauna Loa Record
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OBSERVATION: Surface warming
• Surface temperature has risen about 1 degree F since 1880
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OBSERVATION: Surface warming
• This trend is unique to the industrial age within the last two
+ millennia. Simply suggests new mechanism today.
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A Disagreement: The Hockey Stick
McIntyre & McKitrick
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Threw out 70% of data before 1600
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A Disagreement: The Hockey Stick
McIntyre & McKitrick
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Does not validate against thermometers
(Blue – MBH98; Yel/Grn – M&M; Red - thermometers)
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A Disagreement?
• Is there a disagreement?
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– Not really
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– M&M use inappropriate data and their results do not
validate against instrumental records or pass
standard statistical tests
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– More than a dozen independent reconstructions
have been published (only M&M not peer-reviewed)
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– All but M&M obtained the same qualitative results:
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•
•
•
•
Warm period between 1000 – 1400
Little Ice Age between 1400 - 1900
Unprecedented average temperature last 20 years
Unprecedented rate of warming in the last 20 years
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The ‘Hockey Stick’ in Perspective
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 The hockey stick is not the central piece of
evidence for human-induced climate change
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 Plays a confirmatory role; doesn’t explain change
 Detection (observations) and attribution (modeling)
studies provide the strongest evidence
 The hockey stick is not a sole product of
Michael Mann and his collaborators
 A dozen other studies confirm main conclusions
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 The hockey does not a depict a warm 20th
century overall.
 Early 20th century was cool; late was very warm
 The high rate of change in last half of 20th century
is the take-home message.
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The ‘Hockey Stick’ in Perspective
 Validated against instrumental records
 Based on accepted statistical and
paleoclimatology methods
 Consistent with physical understanding of the
climate system
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 Indicates that the rate of contemporary global
warming is unprecedented over 2000 years
and that it coincides with human activities.
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OBSERVATION: Atmospheric amplification
• Amplification of
surface warming
in the troposphere.
+ • Is it happening? The
tropics show cooling!
+ • Many KNOWN
problems with
+ tropospheric
measurements.
+ • Must ask if the data
are biased.
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RECONCILIATION: Atmospheric amplification
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Warming amplification
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Monthly
Decadal
Data fit
Data
don’t fit
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RECONCILIATION: Atmospheric amplification
 The only data sets that actually conflict with
theory are from satellites and weather balloons,
which contain known biases.
 Not internally consistent: agree with theory on a
short time frame but not on a long time frame and
the departure only occurs in the tropics,
suggesting a systematic drift in the instruments.
 New (Sept. 2005) peer-reviewed studies show that
the discrepancies can be remedied or reduced by
new drift correction methods.
 Within an established scientific framework, bad
data are more common than bad theory.
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OBSERVATION & RECONCILIATION: Ocean
• Ocean heat content
is increasing over time.
+ • Since 1880, the earth
absorbed 0.85 W m-2
+ more energy than it
has emitting to space.
+ • This energy imbalance
is consistent with
enhanced greenhouse
+ effect.
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RECONCILIATION: Modeling for attribution
 Attribution is assigning cause
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 Physics-based (mechanistic) models are
used to see if nonbiased data support theory.
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 Climate models incorporate all major drivers,
both natural and anthropogenic:
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 Natural: solar luminosity, volcanic emissions,
carbon cycle feedbacks
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 Anthropogenic: greenhouse gases, sulfate
aerosols, land use change, carbon cycle
feedbacks
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RECONCILIATION: Modeling for attribution
• Some drivers are
+natural, others are
anthropogenic.
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• Natural drivers force
models to data during
early 20th century.
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• Anthropogenic drivers
force models to the
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data during late 20th
century.
observed
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•Both are REQUIRED!
models
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The Scientific Framework
+• Climate change science
has progressed rapidly
in recent years and we
+ understand climate
change quite well.
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ON
TI
VA )
ER ata
BS (d
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• The holes are mostly
mostly in the data,
+ but are being filled
in quickly of late.
O
• In the end, we have
+ only few holes in the
framework.
(p
ys T H
ica EO
lp R
rin Y
cip
le
s)
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UNDERSTANDING
RECONCILIATION
(data correction
& modeling)
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The Scientific Framework
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 When looking at the framework as whole, one finds
that anomalous observations are exceptional, and
actually are reconcilable in most cases by removing
systematic bias.
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 No plausible alternative theories have been posited
to explain spurious results.
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 When anomalous results fall outside the
established framework and are not used to develop
a new one, they do not lead to new insights.
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For More Information
Pew Center reports:
• The Science of Climate Change: Global and U.S.
Perspectives by Tom Wigley (National Centers for
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Atmospheric Research)
+ • A Synthesis of Potential Climate Change Impacts
on the United States by Joel Smith (Stratus Consulting)
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• Observed Impacts of Global Climate Change in the
U.S. by Camille Parmesan (University of Texas-Austin), and
Hector Galbraith (Galbraith Environmental Sciences and
University of Colorado-Boulder)
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For More Information
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www.pewclimate.org