Attributing and Predicting Climate Change

Transcription

1 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!

2 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

3 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:

4 And now for the next century: carbon dioxide trends Note different scale! Source: IPCC Third Assessment Report

5 Source: IPCC Third Assessment Report, 2001

6 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

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

8 Parameters perturbed Critical Relative Humidity (RHcrit) - related to the cloud cover distribution in a grid box. Accretion constant (CT) - related to growth of rain droplets and lifetime of clouds. Condensation nuclei concentration (CW) - affects water holding capacity and lifetime of clouds. Ice fall velocity (VF1) Parameter: RHcrit CT CW - land CW - sea VF1 Range: ( ) 5x x10-4 1x10-4 2x10-3 2x10-5 5x Standard values 0.7 1x10-4 2x10-4 5x10-5 1

9 Climate Sensitivity

10 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 Standard model set-up Overall Grand Ensemble 10000s 10s 10s Model Versions How do we evaluate all these models? Simulations

11 Estimating effective climate sensitivity from short 2xCO 2 runs Climate Sensitivity: the equilibrium response of globally averaged temperature to a doubling of Carbon Dioxide

12 A shortage of models with high climate sensitivities?

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

14 Initial climateprediction.net experiment Using simplified model ocean to keep runs short 15-year calibration, 15-year control, 15-year 2xCO 2 Double CO2 15 yr, 2 x CO 2 Diagnostics from final 8 yrs. Calibration Derived fluxes 15 yr spin-up 15 yr, base case CO 2 Control

15 Time-evolving frequency distribution Remove models that are unstable in the control. Few remaining negatively drifting 2xCO 2 model versions are an unrealistic consequence of using a slab ocean. Stainforth et al., Nature, Jan. 2005

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

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18 Still they come: climateprediction.net simulations passing initial quality control Traditional range Courtesy of Ben Sanderson

19 Can observations rule out high sensitivities? Bad CMIP-2 coupled models Good Original model Single perturbations Stainforth et al, 2005

20 Responses to Pinatubo forcing blue = 0.5K sensitivity, deep red = 20K sensitivity Frame et al, 2005

21 Uncertainty in global warming under two scenarios of future emissions

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

23 High risk of substantial warming even with today s greenhouse gas levels Can we really talk about a safe stabilisation limit?

24 Regional responses: temperature and precipitation Standard model version Low sensitivity model High sensitivity model

25 Regional Behaviour European Precipitation Mediterranean Basin Northern Europe Winter Winter Summer Summer Annual Annual Unpublished analysis from climateprediction.net: Source: David Stainforth

26 September 2003 climateprediction.net classic experiment launched June 2004 Thermohaline circulation experiment distributed

27 September 2003 climateprediction.net classic experiment launched June 2004 Thermohaline circulation experiment distributed August 2004 climateprediction.net goes BOINC Berkeley Open Infrastructure for Network Computing

28 Climateprediction.net: the world s largest climate modelling facility Since September 2003, 105,000 participants in 142 countries (514 in Russia) have completed 115, year GCM runs computed 8 million model years donated 8,000 years of computing time

29 The most powerful computer in the world?

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

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32 All climateprediction.net results are available to any scientist who wants to propose some analysis

33 Current experiment: September 2005 Sulphur cycle experiment launched

34 Future Experiments: February Full coupled ocean-atmosphere run to be launched Climate change season: January May 2006 How well does each model do at reproducing the climate of ? Find out which models we believe more than others What climate does each model predict for ? A probability-based climate forecast for the 21 st century

35 Future Experiments: End of 2006 PRoviding REgional Climate for Impact Studies (PRECIS) regional model included Scientists in any country can propose a region of interest Regional model embedded in GCM distributed Public decides which region they want to model Results returned to proposing scientists for analysis

36 Record hot events are more likely in a generally warmer world

37 Summer 2003 temperatures relative to From NASA s MODIS - Moderate Resolution Imaging Spectrometer, courtesy of Reto Stöckli, ETHZ

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

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

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

41 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

42 South Oxford on January 5 th, 2003 Photo courtesy of Dave Mitchell Climate is what you expect, weather is what you get (Lorenz)

43 Model-simulated changes in extreme rainfall in southern England 4-year event 12-year event year event

44 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) 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.

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

46 But what could be done? How can an oil company or coal miner avoid selling a product whose use involves increasing atmospheric CO 2? 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)

47 But what could be done? 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. The technology to capture and remove carbon dioxide from the atmosphere exists and is already in use. It would double or even treble the cost of fossil fuels.