Climate Change : The State of Knowledge

Climate Adaptation National Research Flagship Bryson Bates Leader, Pathways to Adaptation Theme 22 April 2009

Presentation outline ●

Human vs geological time scales

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Observed global trends

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Observed national trends Climate change projections for WA

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Extremes

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Concluding remarks

Drivers of climate change

Climate has always changed

Geologic & human time scales      

Past super-greenhouse conditions:

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50 My BP CO 2 ~ 1,000 ppm; above present no polar ice; sea level ~ 120 m 250 My BP CO 2 ~ 10 to 20 x present level (~ 385 ppm); 95% extinction rate 50 to Advent of humans ~ 2.2 to 2.4 My BP Civilisation started ~ 12 Ky BP Current rate CO 2 650 Ky increase 200 x faster than that over last Without mitigation & abatement, burning all known coal reserves will raise atmospheric CO 2 ~ 2,000 ppm Estimated arrival time for next ice age: ‘now’ to 20 Ky

Enhanced greenhouse effect 

GHGs are a natural part of the atmosphere: support life

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Water vapour is most abundant GHG: humans have little impact

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Humans have most impact on CO 2 , CH 4 , N 2 O: net effect

30 25 20 15 10 Actual emissions: CDIAC 450ppm stabilisation 650ppm stabilisation A1FI A1B A1T A2 B1 B2 10 5 0

Recent emissions

1850 1900 1950 2000 2050 9 8 7 6 5 1990 2100 Actual emissions: CDIAC Actual emissions: EIA 450ppm stabilisation 650ppm stabilisation A1FI A1B A1T A2 B1 B2 1995 2006 2005 2007

Global Carbon Budget update; Raupach et al. 2007, PNAS

2000 2005 2010

SRES (2000) growth rates in % y -1 for 2000-2010: A1B: 2.42

A1FI : 2.71

A1T: 1.63

A2: 2.13

B1: 1.79

B2: 1.61

Observed 2000-2006 3.3%

Observations vs IPCC projections

Rahmstorf et al. (2007)

Observations vs IPCC projections

Rahmstorf et al. (2007)

Global average temperatures are rising

Global average temperatures are rising

Global average temperatures are rising

Lags in the response of climate to emissions

IPCC 2001, SYM, Figure 8.3

Past 12 years have been unusual

Very wet in the north & west Very dry over southeast Qld, southern NSW and SA, Victoria, eastern Tas and southwest WA CSIRO

Climate change: the latest science

Feb 1997 – Jan 2009

Minimum & maximum temperatures

Temperature projections (2050)

B1 Winter A1B A1F1 B1 Summer A1B A1FI 23 GCMs; 1980 –1999 baseline Source: http://www.climatechangeinaustralia.gov.au/

Wind speed projections (2050)

B1 Winter A1B A1F1 B1 Summer A1B A1FI 23 GCMs; 1980 –1999 baseline Source: http://www.climatechangeinaustralia.gov.au/

Rainfall projections (2050)

B1 Winter A1B A1F1 B1 Summer A1B A1FI 23 GCMs; 1980 –1999 baseline Source: http://www.climatechangeinaustralia.gov.au/

Specific projections ●

SW rainfall projected to decrease by 2 to 20% by 2030 & 5 to 60% by 2070

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SW summer temperatures projected to increase between 0.5 to 2.1 ºC by 2030 & 1 to 6.5 ºC by 2070

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Average annual number of days above 35 ºC in Perth to increase from 28 to 36-67 by 2070

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SW winter temperatures projected to increase between 0.5 & 2 ºC by 2030 & 1 & 5.5 ºC by 2070

Potential impacts of climate change Greater risks to major infrastructure due to increases in extreme weather events

More 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)

Key points on weather & climate extremes ●

Infrequent events at either the low or high end of a variable of interest – low probability, high impact

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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

Climate change & extremes 0 2 4 Climate variable 6 8

How will changes in extremes be manifested?

Rainfall extremes ●

Occur on different scales in space-time

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intermittent processes

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poor observations Not 'resolved' by computational grids in GCMs – need 'downscaling' methods

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topographic effects coastal effects subgrid-scale processes (e.g. convection)

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Changes do not scale with specific humidity changes: more complex

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Statistics vary over a range of time scales (temporal clustering)

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Changes in rainfall means cannot be used to reliably infer changes in extremes

2030

Value added by dynamical downscaling

200 km 65 km 4 km fraction 2070

Concluding remarks 

Our climate will continue to change due to natural & human-induced forcing

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Present evidence for climate change is compelling

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Prognosis for WA is hotter, & drier for SW (NW uncertain) Climate/weather extremes – an active area of research difficult topic & Believe/disbelieve – stay informed & manage the risk

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Future management strategies will need to be:

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adaptive rather than static

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based on a scenario & portfolio approach