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Climate Change : The State of Knowledge
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Transcript of Climate Change : The State of Knowledge
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Climate Change : The State of Knowledge
Bryson Bates
Leader, Pathways to Adaptation Theme
22 April 2009
Climate Adaptation National Research Flagship
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Presentation outline
● Human vs geological time scales
● Observed global trends
● Observed national trends
● Climate change projections for WA
● Extremes
● Concluding remarks
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Drivers of climate change
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Climate has always changed
New
Scientist, 2008
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Geologic & human time scales
Past super-greenhouse conditions: 50 My BP CO2~ 1,000 ppm; no polar ice; sea level ~ 120 m
above present
250 My BP CO2~ 10 to 20 x present level (~ 385 ppm); 50 to 95% extinction rate
Advent of humans ~ 2.2 to 2.4 My BP Civilisation started ~ 12 Ky BP Current rate CO2 increase 200 x faster than that over last
650 Ky Without mitigation & abatement, burning all known coal
reserves will raise atmospheric CO2 ~ 2,000 ppm
Estimated arrival time for next ice age: ‘now’ to 20 Ky
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Enhanced greenhouse effect
GHGs are a natural part of the atmosphere: support life
Water vapour is most abundant GHG: humans have little impact
Humans have most impact on CO2, CH4, N2O: net effect
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Global fossil fuel emissions
SRES (2000) growth rates in % y -1 for 2000-2010:
A1B: 2.42 A1FI: 2.71A1T: 1.63A2: 2.13B1: 1.79B2: 1.61
Observed 2000-2006 3.3%
Recent emissions
1990 1995 2000 2005 2010
CO
2 E
mis
sion
s (G
tC y
-1)
5
6
7
8
9
10Actual emissions: CDIACActual emissions: EIA450ppm stabilisation650ppm stabilisationA1FI A1B A1T A2 B1 B2
1850 1900 1950 2000 2050 2100C
O2 E
mis
sion
s (G
tC y
-1)
0
5
10
15
20
25
30Actual emissions: CDIAC450ppm stabilisation650ppm stabilisationA1FI A1B A1T A2 B1 B2
20062005
2007
Global Carbon Budget update; Raupach et al. 2007, PNAS
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Observations vs IPCC projections
Rahmstorf et al. (2007)
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Rahmstorf et al. (2007)
Observations vs IPCC projections
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Global average temperatures are rising
CR
U, U
EA
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Global average temperatures are rising
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Global average temperatures are rising
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Lags in the response of climate to emissions
IPCC 2001, SYM, Figure 8.3
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Past 12 years have been unusual
CSIRO Climate change: the latest science
Very wet in the north & west
Very dry over southeast Qld, southern NSW and SA, Victoria, eastern Tas and southwest WA
Feb 1997 – Jan 2009
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Minimum & maximum temperatures
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Temperature projections (2050)
Winter Summer
B1 B1A1B A1BA1F1 A1FI
23 GCMs; 1980–1999 baselineSource: http://www.climatechangeinaustralia.gov.au/
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Wind speed projections (2050)
Winter Summer
B1 B1A1B A1BA1F1 A1FI
23 GCMs; 1980–1999 baselineSource: http://www.climatechangeinaustralia.gov.au/
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Rainfall projections (2050)
Winter Summer
B1 B1A1B A1BA1F1 A1FI
23 GCMs; 1980–1999 baselineSource: http://www.climatechangeinaustralia.gov.au/
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Specific projections
● SW rainfall projected to decrease by 2 to 20% by 2030 & 5 to 60% by 2070
● SW summer temperatures projected to increase between 0.5 to 2.1 ºC by 2030 & 1 to 6.5 ºC by 2070
● Average annual number of days above 35 ºC in Perth to increase from 28 to 36-67 by 2070
● SW winter temperatures projected to increase between 0.5 & 2 ºC by 2030 & 1 & 5.5 ºC by 2070
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Potential impacts of climate change
Greater risks to major infrastructure due to increases in extreme weather eventsMore damage to buildings; transport, energy & water services; telecommunications
More heat-related deaths for people aged over 65 1115 deaths per year at present in the 5 largest capital cities, increasing to 2300-2500 per year by 2020
Greater risks for coastal flooding from sea-level rise and storm surges(global sea level rise of 1 metre or more possible by 2100)
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Key points on weather & climate extremes
● Infrequent events at either the low or high end of a variable of interest – low probability, high impact
● Small change in average of a variable can be accompanied by large changes in I-F-D characteristics
● Wide range possible within unchanging climate – difficult to attribute individual event to climate change
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Climate change & extremes
0 2 4 6 8
0.0
0.1
0.2
0.3
0.4
0.5
Climate variable
Fre
quen
cy
How will changes in
extremes be manifested?
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Rainfall extremes
● Occur on different scales in space-time● intermittent processes
● poor observations
● Not 'resolved' by computational grids in GCMs – need 'downscaling' methods
● topographic effects
● coastal effects
● subgrid-scale processes (e.g. convection)
● Changes do not scale with specific humidity changes: more complex
● Statistics vary over a range of time scales (temporal clustering)
● Changes in rainfall means cannot be used to reliably infer changes in extremes
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Value added by dynamical downscaling
200 km 65 km 4 km
2030
2070
fraction
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Concluding remarks
Our climate will continue to change due to natural & human-induced forcing
Present evidence for climate change is compelling
Prognosis for WA is hotter, & drier for SW (NW uncertain)
Climate/weather extremes – difficult topic & an active area of research
Believe/disbelieve – stay informed & manage the risk
Future management strategies will need to be:
adaptive rather than static based on a scenario & portfolio approach