Climate Change : The State of Knowledge

Bryson Bates

Leader, Pathways to Adaptation Theme

22 April 2009

Climate Adaptation National Research Flagship

Presentation outline

● Human vs geological time scales

● Observed global trends

● Observed national trends

● Climate change projections for WA

● Extremes

● Concluding remarks

Drivers of climate change

Climate has always changed

New

Scientist, 2008

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

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

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

Observations vs IPCC projections

Rahmstorf et al. (2007)

Rahmstorf et al. (2007)

Observations vs IPCC projections

Global average temperatures are rising

CR

U, U

EA

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

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

Minimum & maximum temperatures

Temperature projections (2050)

Winter Summer

B1 B1A1B A1BA1F1 A1FI

23 GCMs; 1980–1999 baselineSource: http://www.climatechangeinaustralia.gov.au/

Wind speed projections (2050)

Winter Summer

B1 B1A1B A1BA1F1 A1FI

23 GCMs; 1980–1999 baselineSource: http://www.climatechangeinaustralia.gov.au/

Rainfall projections (2050)

Winter Summer

B1 B1A1B A1BA1F1 A1FI

23 GCMs; 1980–1999 baselineSource: http://www.climatechangeinaustralia.gov.au/

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

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)

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

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?

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

Value added by dynamical downscaling

200 km 65 km 4 km

2030

2070

fraction

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