university of oxford uncertainty in climate science: what it means for the current debate myles...
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University of Oxford
Uncertainty in climate science:what it means for the current debate
Myles AllenDepartment of Physics, University of Oxford
University of Oxford
Three kinds of uncertainty
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?
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Copenhagen Diagnosis
Big picture: global emissions continue to rise
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And the climate system continues to warm – on multi-decade if not sub-decade timescales
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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
Global temperature response to greenhouse gases and aerosolsSolid: climate model simulationDashed: recalibrated prediction using HadISST & CRUTEM data to August 1996(Allen et al, 2000)14 years
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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
Global temperature response to greenhouse gases and aerosolsSolid: climate model simulationDashed: recalibrated prediction using HadISST & CRUTEM data to August 1996(Allen et al, 2000)14 years
University of Oxford
Uncertainty in projected warming over the next few decades
Global temperature response to greenhouse gases and aerosolsSolid: climate model simulationDashed: recalibrated prediction using HadISST & CRUTEM data to August 1996(Allen et al, 2000)Forecast verification 01/01/00 to 31/12/09
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But what does this mean for flood risk in OX1?
South Oxford on January 5th, 2003
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oto
: Da
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ll
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Models predict increasing winter rainfall in North West Europe over the next 80 years
Figure 10.9
IPCC
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Are recent UK floods affected by climate change? Pall et al 2010
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 forecast-resolution 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
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.