4°C g
global warming:
g
regional patterns and timing
Richard Betts, Mike Sanderson, Debbie Hemming,
Mark New, Jason Lowe, Chris Jones
© Crown copyright Met Office
4°C+ conference, Oxford University, 25.9.09
IPCC SRES emissions scenarios
© Crown copyright Met Office
Van Vuuren
and Riahi
(2008)
1
Model projections of global warming with
IPCC SRES emissions scenarios
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IPCC (2007)
Comparison of SRES scenarios with
actual emissions
© Crown copyright Met Office
Van Vuuren
and Riahi
(2008)
2
Using climate model ensembles to
assess confidence in projections
• Multi-model ensemble: set of (mostly) different models
• IPCC 4th Assessment Report (AR4) – 23 models
• Perturbed physics ensembles: set of variants of one model
• ClimatePrediction.net – HadCM3 model (1500+ variants)
• Met Office Hadley Centre (MOHC) “QUMP” project – HadCM3 model
(17 variants)
• Simple
Si l climate
li t model
d l ttuned
d tto th
the above
b
complex
l models
d l
• IPCC “likely range of warming” statements
• Combination of the above
• UKCP09 – mostly HadCM3, with some input from IPCC AR4 models
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A1B
scenario
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3
Global warming with A1B scenario:
all IPCC models
“High
High-end
end”::
simulations
with 4°C
warming by
by 2090s
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Pattern of warming by 2090s, A1B
Mean of “high-end” IPCC simulations
(3 models, mean global warming 4.3°C)
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Temperature change (°C) relative to 1961-1990
4
Precipitation changes by 2090s, A1B
Mean of “high-end” IPCC simulations
(3 models, mean global warming 4.3°C)
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Precipitation change (%) relative to 1961-1990
Global warming with A1B scenario:
MOHC ensemble
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5
Pattern of warming by 2090s, A1B
Mean of “high-end” MOHC simulations
(9 simulations, mean global warming 4.6°C)
© Crown copyright Met Office
Temperature change (°C) relative to 1961-1990
Precipitation changes by 2090s, A1B
Mean of “high-end” MOHC simulations
(9 simulations, mean global warming 4.6°C)
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Precipitation change (%) relative to 1961-1990
6
A1FI
scenario
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Pattern of warming by 2090s, A1FI
Mean of “high-end” MOHC simulations
(14 simulations, mean global warming 5.4°C)
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Temperature change (°C) relative to 1961-1990
7
Precipitation changes by 2090s, A1FI
Mean of “high-end” MOHC simulations
(14 simulations, mean global warming 5.4°C)
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Global warming with A1FI scenario:
MOHC ensemble
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8
Importance of carbon sinks for slowing
CO2 rise
Emissions
Change in atmospheric
concentration
IPCC (2007)
© Crown copyright Met Office
Carbon remo
ovals from atmosphere (G
Gt C)
The free ecosystem service that has
been buying us time may not last…
100
Carbon uptake by plants in 20th
centuryy has buffered the p
past
CO2 rise
50
0
But climate change
may put this into
reverse
–50
50
–100
Cox et al
(2000)
–150
1850
1900
vegetation carbon
soil carbon
1950
2000
2050
2100
© Crown copyright Met Office
9
Effects of climate-carbon cycle
feedbacks on atmospheric CO2 rise
with CO2-climate feedbacks
without CO2-climate feedbacks
CO2 conc
centrations (ppmv)
1000
Cox et al
(2000)
IS92a “business-as-usual” scenario
800
600
400
200
1900
1950
2000
2050
2100
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Multi-model assessment of carbon
cycle feedbacks (C4MIP):
A2 emissions scenario
Friedlingstein
et al (2006)
© Crown copyright Met Office
10
Range of global warming projections
for A1FI (high emissions) scenario,
including carbon cycle feedbacks
Simple
model
tuned to complex
Global mean
temperature:
SRES A1FImodels,
consistent with IPCC method
8
90th %ile
6
median
5
10th %ile
4
3
2
o
C abo
ove pre-industrial
7
1
0
1980
2000
2020
2040
2060
2080
2100
Year
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Exceedance of global warming
thresholds, A1B, no carbon cycle
feedbacks: ClimatePrediction.net
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11
Conclusions
• Current CO2 emissions are near (but not above) upper end of IPCC
scenarios
i
• 4°C global warming (relative to pre-industrial) is possible by the
2090s, especially under high emissions scenario
• Many areas could warm by 10°C or more
• The Arctic could warm by 15°C or more
• Annual precipitation could decrease by 20% or more in many areas
• Carbon cycle feedbacks expected to accelerate warming
• With high emissions, best guess is 4°C in 2070s
• Plausible worst case: 4°C by 2060
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