Indirect (secondary and tertiary) effects of pressures on climate

2011

Direct effects on climate, such as those outlined in Section 2.2.3, trigger indirect effects further down a complex chain of cause and effect. These are products of the profound and pervasive influence of climate, both on a host of natural processes that underpin the condition and trend of ecosystems, and on a range of demographic, economic and social processes and systems. The complex nature of the effects of changes in climate is illustrated in Figure 3.16 in relation to human health.

Australia’s Fifth national communication on climate change (under the United Nations Framework Convention on Climate Change)42 draws on the work of the IPCC25 to outline a wide range of indirect effects of climate change:

  • decreased water availability and water security, due to
    • reduced rainfall in southern Australia and south-west Western Australia
    • increased evaporation, which reduces run-off to streams and recharge of groundwater systems
  • coastal zone impacts, such as inundation from sea level rise
  • damage to energy, water, communications and built infrastructure
  • a decline in agricultural productivity due to increased drought and fire
  • damage to iconic natural ecosystems, such as the Great Barrier Reef and Kakadu National Park
  • a decline in biodiversity.

Other sources identify additional indirect effects of climate change, such as:

  • likely increases in the frequency of days of extreme bushfire risk,5658 and of dust storms, linked to widespread reductions in levels of soil moisture25
  • changes to human health, including
    • some positive, particularly in the first part of the century, when some areas will benefit from a reduction in cold weather
    • some negative, resulting from factors such as more frequent and intense heatwaves, particularly later in the century (Table 3.1), and possible extension in the range of various disease vectors (notably mosquitoes).13,25,59

In the baseline case, any increase in number of deaths is due to the expanding and ageing of the population. The next three cases are best-estimate cases and use the 50th percentile rainfall and relative humidity and 50th percentile temperature for Australia. The final case (right-hand side) is an illustrative ‘bad-end story’ that uses the 10th percentile rainfall and relative humidity and 90th percentile temperature for Australia (a hot, dry extreme).

  Baseline—no human-induced climate change No-mitigation case Global mitigation with CO2-e stabilisation at 550 ppm by 2100 Global mitigation with CO2-e stabilisation at 450 ppm by 2100 Hot, dry extreme case
  Number of temperature-related deaths in 2030 and 2100
Region 2030 2100 2030 2100 2030 2100 2030 2100 2030 2100
ACT 300 333 280 250 278 285 276 295 275 262
NSW 2 552 2  754 2 316 1 906  2  290 2  224 2  268 2  334 2  255 2 040 
NT 63 61 63 407 63 93 64 76 64 768
Qld 1  399 1  747 1  276 5 878  1  274 1  825 1  278 1  664 1  286 11 322
SA 806 811 770 704 766 735 762 750 758 740
Tas 390 375 360 240 357 313 354 327 352 211
Vic 1  788 1  966 1  632 1 164  1  614 1  586 1  599 1  673 1  589 1 021 
WA 419 515 418 685 419 529 419 519 420 835
Australia 7  717 8  562 7  115 11 234 7  061 7  590 7  020 7  638 6  999 17 199

ACT = Australian Capital Territory; CO2-e = carbon dioxide equivalent; NSW = New South Wales; NT = Northern Territory; ppm = parts per million; Qld = Queensland; SA = South Australia; Tas = Tasmania; Vic = Victoria; WA = Western Australia

Source: Garnaut13

Box 3.3 Victorian heatwave, January 2009

During the second half of January 2009, Victoria experienced an unprecedented heatwave. Maximum day-time and night-time temperature records were broken by significant margins, and new records were set for the duration of extreme heat. From 27 to 31 January, much of Victoria experienced maximum temperatures 12–15 °C above normal. For three of these days (28–30 January), the maximum was above 43 °C, peaking at 45.1 °C on January 30.

Table A Temperatures in Victoria, 26 January – 1 February 2009
  Maximum day-time temperature (°C) Maximum night-time temperature (°C) Mean temperature (°C)
Monday 26 January 25.5 14.4 19.9
Tuesday 27 January 36.4 16.6 26.5
Wednesday 28 January 43.4 18.8 31.1
Thursday 29 January 44.3 25.7 35.0
Friday 30 January 45.1 25.7 35.4
Saturday 31 January 30.5 22.5 26.5
Sunday 1 February 33.8 20.3 27.0

The impact of the heatwave on public health was clearly identifiable and substantial. The effects were similar to those of the catastrophic 2003 European heatwave, which had an estimated total excess mortality of 70 000. In Victoria, the Department of Health calculated a figure of 374 excess deaths over the average number in the same weeks of the preceding five years (an increase of 62% in all-cause mortality).

In addition to this marked spike in mortality, there was a pronounced impact on morbidity, which was reflected in increases in ambulance emergency case load (46% over the three hottest days), locum general practitioner visits (almost four-fold increase in heat-related attendances), and emergency room attendances (eight-fold increase in heat-related presentations). Not surprisingly, as shown in Figure A, the elderly were the group most affected, with people over 75 years of age being disproportionately represented in both mortality and morbidity.

As with any extreme climatic event, estimating the extent to which climate change played a role over and above natural variability is problematic. Nevertheless, an increase in the frequency of such extreme temperature-driven events is entirely consistent with the now decades-long upward trend of average temperatures and with the results from studies modelling a broad range of climate change scenarios.

(2011). Climate: Indirect (secondary and tertiary) effects of pressures on climate . In: Australia state of the environment 2011, Australian Government Department of the Environment and Energy, Canberra, https://soe.environment.gov.au/theme/climate/topic/indirect-secondary-and-tertiary-effects-pressures-climate, DOI 10.4226/94/58b65c70bc372