Transcript Myles Allen slideshow no.1

Uncertainty in climate science:
what it means for the current debate
Myles Allen
Department of Physics, University of Oxford
[email protected]
University of Oxford
Three kinds of uncertainty
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Big picture uncertainty: what is the chance that
climate scientists have got it all wrong?
Large-scale projection uncertainty: how much global
warming should we expect over the coming decades
and centuries?
Small-scale prediction uncertainty: what does this
mean for flood risk in OX1/OX2?
University of Oxford
Big picture: global emissions continue to rise
Copenhagen Diagnosis
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And the climate system continues to warm – on
multi-decade if not sub-decade timescales
University of Oxford
January 2010 – the warmest on record:
but not everywhere
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But can we trust the record?
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Yes. The impact of the “climategate” revelations
on the instrumental temperature record
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Multiple indicators of “unequivocal” warming:
Arctic sea ice in September 2005 & 2007
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Uncertainty in projected warming over the next
few decades
14 years
Global temperature
response to
greenhouse gases
and aerosols
Solid: climate model
simulation
Dashed: recalibrated
prediction using
HadISST & CRUTEM
data to August 1996
(Allen et al, 2000)
University of Oxford
There was a time when people took 14-year
climate forecasts seriously
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The article in question
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Uncertainty in projected warming over the next
few decades
14 years
Global temperature
response to
greenhouse gases
and aerosols
Solid: climate model
simulation
Dashed: recalibrated
prediction using
HadISST & CRUTEM
data to August 1996
(Allen et al, 2000)
University of Oxford
Uncertainty in projected warming over the next
few decades
Global temperature
response to
greenhouse gases
and aerosols
Solid: climate model
simulation
Dashed: recalibrated
prediction using
HadISST & CRUTEM
data to August 1996
(Allen et al, 2000)
Forecast verification
01/01/00 to 31/12/09
University of Oxford
Photo: Dave Mitchell
But what does this mean for flood risk in OX1?
South Oxford on January 5th, 2003
University of Oxford
Models predict increasing winter rainfall in North
West Europe over the next 80 years
IPCC
University of Oxford
Are recent UK floods affected by climate
change? Pall et al 2010
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Aim: to quantify the role of increased greenhouse
gases in precipitation responsible for 2000 floods.
Challenge: relatively unlikely event even given 2000
climate drivers and sea surface temperatures (SSTs).
Approach: large (multi-thousand-member) ensemble
simulation of April 2000 – March 2001 using forecastresolution global model (90km resolution near UK).
Identical “non-industrial” ensemble removing the
influence of increased greenhouse gases, including
attributable SST change, allowing for uncertainty.
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Performing simulations using distributed
computing: climateprediction.net
>300,000 volunteers (50,000 active), 90M model-years
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Autumn 2000
in the ERA-40
reanalysis…
…and in one
of the wetter
members of
our ensemble.
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Risk of floods in the year 2000, with and without
the influence of increased greenhouse gases
2x increase in risk
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Uncertainties in the science: the current state of
play
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Uncertainty in basic causes is climate change is
relatively low: IPCC (2007) concluded human
influence was “very likely” the cause of most of the
warming over the past 50 years – meaning a 10%
chance that it wasn’t.
Uncertainty in large-scale trends still around a factor
of two – meaning changes predicted for 2040 might
occur in 2030 or 2050 – does this matter?
Uncertainty in the impacts of climate change, and
the costs for nations, organisations and individuals,
are still very high.
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