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Attributing and Predicting Climate Change Sylvia Knight climateprediction.net Atmospheric, Oceanic and Planetary Physics, University of Oxford

Tolu Aina, Myles Allen, Carl Christensen, Dave Frame, Ellie Highwood, Jamie Kettleborough, Claudio Piani, Neil Massey, Ben Sanderson, Bob Spicer, David Stainforth, Daíthí Stone. and about 100,000 other people worldwide!

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“In the light of new evidence and taking into account the remaining uncertainties, most of the observed warming over the last 50 years is likely (meaning a better than a 2 in 3 chance) to have been due to the increase in greenhouse gas concentrations” Source: IPCC Third Assessment Report, 2001

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Hindcasting Past Climate Anthropogenic only:

Despite the vast complexity of climate models they can simulate the observed climate change in some global variables very well. All:

Natural only:

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And now for the next century: carbon dioxide trends

Note different scale! Source: IPCC Third Assessment Report

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Source: IPCC Third Assessment Report, 2001 Oxford University

2080 temperature change (K)

2080 precipitation change (%)

We can produce very detailed predictions of climate change with no idea of how reliable they might be Source: Dr. Mat Collins, Hadley Centre

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Sources of Uncertainty and How to Include Them In a Climate Forecast „

Natural Variability: The climate is chaotic with variations on timescales from minutes to centuries. Solution: Initial Condition Ensembles

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Forcing uncertainty: Changes due to factors external to the climate system e.g. greenhouse gas emissions (natural and anthropogenic), solar radiation etc. Solution: Scenarios for possible futures.

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Model uncertainty: Different models could be as could at simulating the past but give a different forecast for the future? Solution: Perturbed-Physics Ensembles

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The problem with dealing with uncertainty in climate change prediction Objective: find as many as possible alternative, equally realistic, model versions that respond differently to increasing carbon dioxide, to explore the full range of possibilities. Perturbed Physics Ensemble

Initial Condition Ensemble

Forcing Ensemble

Overall Grand Ensemble

Standard model set-up

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10000s

Model Versions

10s

10s

Simulations Oxford University

Estimating effective climate sensitivity from short 2xCO2 runs

Climate Sensitivity: the equilibrium response of globally averaged temperature to a doubling of Carbon Dioxide Oxford University

A shortage of models with high climate sensitivities?

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Ranges of opinion in climate sensitivity (Morgan and Keith, 1995)

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Initial climateprediction.net experiment „ „

Using simplified model ocean to keep runs short 15-year calibration, 15-year control, 15-year 2xCO2

Double CO2 15 yr, 2 x CO2

Calibration 15 yr spin-up

Diagnostics from final 8 yrs.

Derived fluxes

15 yr, base case CO2

Control

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Time-evolving frequency distribution Remove models that are unstable in the control.

Few remaining negatively drifting 2xCO2 model versions are an unrealistic consequence of using a slab ocean.

Stainforth et al., Nature, 2005 Oxford University

Not The Day After Tomorrow: why we got some negative sensitivities…

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Still they come: 47334 climateprediction.net simulations passing initial quality control

Traditional range

Courtesy of Ben Sanderson Oxford University

Can observations rule out high sensitivities? Bad CMIP-2 coupled models

Original model

Single perturbations

Good

Stainforth et al, 2005

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Responses to Pinatubo forcing blue = 0.5K sensitivity, deep red = 20K sensitivity

Frame et al, 2005

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Uncertainty in global warming under two scenarios of future emissions

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High risk of substantial warming even with today’s greenhouse gas levels

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High risk of substantial warming even with today’s greenhouse gas levels

Can we really talk about a ‘safe’ stabilisation limit?

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Regional responses: temperature and precipitation Standard model version

Low sensitivity model

High sensitivity model

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Regional Behaviour – European Precipitation Mediterranean Basin

Northern Europe

Winter Winter

Summer Summer

Annual

Annual

Unpublished analysis from climateprediction.net: Source: David Stainforth

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Record hot events are more likely in a generally warmer world

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Summer 2003 temperatures relative to 2000-2004

From NASA’s MODIS - Moderate Resolution Imaging Spectrometer, courtesy of Reto Stöckli, ETHZ

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Heat-wave blamed for US$12.3 billion uninsured crop losses + US$1.6 billion forest fire damage

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Excess mortality rates in early August 2003 indicate 22,000 - 35,000 heat-related deaths

Daily mortality in Baden-Württemberg Oxford University

But a single heat-wave is a weather event: how can we pin down the role of climate change? „

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The immediate cause of the heat-wave was a persistent anti-cyclone over Northwest Europe. There is still no evidence that human influence on climate makes such circulation patterns more likely. Instead, we ask how human influence on climate has affected the risk of such a weather event (however induced) causing such an intense heat-wave?

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Was the hot summer of 2003 due to climate change?

Anthropogenic emissions of greenhouse gases have at least doubled the risk of a summer like 2003 By 2050, it could be that hot every other summer Stott, Stone & Allen, Nature, 2004 Oxford University

Photo courtesy of Dave Mitchell

South Oxford on January 5th, 2003

“Climate is what you expect, weather is what you get” (Lorenz)

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Model-simulated changes in extreme rainfall in southern England

4-year event

12-year event

2090 2000

1860

30-year event

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“Plaintiffs ... must show that, more probably than not, their individual injuries were caused by the risk factor in question, as opposed to any other cause. This has sometimes been translated to a requirement of a relative risk of at least two.” (Grossman, 2003) „

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The contribution of past greenhouse gas emissions to some current climate risks may already exceed 50%, the threshold for civil tort actions. Over the coming decade, both the cost and the inevitability of climate change will become clearer, fuelling demands for compensation for: – – – –

Flooding Heat wave damages and deaths Threats to water supplies, especially from glacial sources Coastal erosion etc. Oxford University

By the 2030s, >50% of anthopogenic GHG loading will be due to post-1990 emissions

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But what could be done? „

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How can an oil company or coal miner avoid selling a product whose use involves increasing atmospheric CO2? Simple: they bury (“sequester”) the equivalent amount of carbon. Of course, this would make oil or coal more expensive, which would hurt – but how much? “All OECD countries besides the US impose big taxes on fuel, but curiously it hasn’t reduced consumption.” Lord Browne, BP (Financial Times)

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But what could be done? „

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Fossil fuels are still remarkably cheap, since we pay for the cost of extraction (and cartel-like profits), not the cost of their impact. If politicians were to apply the “Polluter Pays Principle” to producers of fossil fuels, this would change rapidly: it might well make more sense to sell carbon-neutral fuel than risk liability.

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Climateprediction.net: the world’s largest climate modelling facility

Since September 2003, 105,000 participants in 142 countries (20,000 in Germany) have completed 106,000 45 -year GCM runs computed 7 million model years donated 8,000 years of computing time Oxford University

Members of the public download and run a full 3-D climate model on their personal computers

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www.climateprediction.net

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