The Chief Scientist Discusses Questions Regarding the Current Floods and Australia’s Climate. (January 28, 2011)

A fortnight ago Australia's Chief Scientist, Professor Penny Sackett contributed an opinion piece to The Sydney Morning Herald regarding what science can contribute to the understanding of the events leading up to the flooding of so much of the nation.

Below we reprint Professor Sackett's appraisal as presented on her blog of January 18, 2011.

Why did this happen? Why now? Why here? Science can’t yet answer all the questions that will be asked, but I have tried to anticipate some questions where current science can shed some light.

Are these floods unusual or rare? 

Summer floods of this magnitude are rather rare.  For example, many parts of Queensland are now experiencing their highest-ever recorded floods ^{1, 2}, while other areas are feeling floods of a size that have occurred only a few times over the last century ^{3, 4}.  Scientists at the Bureau of Meteorology, however, are not surprised that Australia is witnessing strong flooding now as La Niña periods often bring widespread rain and flooding to our country^{5, 6, 7}.

La Niña is a natural driver of climate variability that occurs when the temperature of the surface of the central to eastern Pacific Ocean is significantly lower than normal.  During La Niña, different parts of the Earth experience particular changes in local climate for a period of time (generally a year).  In Australia, this typically means cooler than normal temperatures and increased winter, spring and summer rainfall, particularly over eastern and northern Australia^{5, 7}.  La Niña is contrasted with its opposite condition called El Niño, which is associated with an increased risk of dry conditions and warmer temperatures across large areas of Australia, often resulting in major drought, the brunt of which Australia has also felt in the past.

At the moment, we are experiencing a very strong La Niña event.  Records from the Bureau of Meteorology show that most of Australia’s worst floods have occurred during La Niña periods⁶, (including the previous strong La Niña events in 1955 and 1974) when widespread and severe flooding occurred in eastern Australia².  The current strong La Niña period we are now experiencing is expected to last for a few more months yet, with La Niña events typically ending in the Australian autumn⁸.

Is this flooding due to climate change induced by long-term global warming?

International scientists have found that El Niño and La Niña events have been occurring for quite some time, long before the most recent effects of global warming9.  So it is important to not confuse the local and short-term climate variability that is associated with El Niño and La Niña events, with the longer term pattern of climate change.

However, since precipitation levels are linked to how much water vapour is in the air, the long-term heating of the world’s oceans due to global warming may be associated with heavier monsoons¹⁰.  As for La Niña itself, we don’t yet know how climate change will affect its patterns and strength.  Scientists are actively investigating possible connections, but the exact mechanisms and effects are yet to be understood.  Their work is of vital importance, particularly to Australians.

While the question of how the future pattern of La Nina and other ocean events may change as the earth warms is a matter of study, scientists are reasonably confident that global warming will be associated with an increase in the severity or frequency of many types of severe weather and related events such as floods, droughts, cyclones and bushfires^{11, 12}.

Since localised geography affects weather patterns, different types of extreme events will take place at different places around the globe.  For example, mountain ranges and ocean currents have large, but different impacts on the weather patterns in their local regions.  In Australia, the effects of long-term climate change make it likely that south-eastern Australia and many parts of western Australia will experience more frequent and more severe droughts, whereas northern Australia may experience more severe monsoonal rains, tropical storms and flooding due to storm surges^11,12.

Given the power of nature, a nature that sustains us and challenges us, it is not possible to avoid all impacts of extreme weather events, whether they be caused by short-term climate variability like La Niña, or longer-term changes in the whole earth system, such as global warming.   Where we can help to avoid increased extreme weather events, by acting to mitigate climate change caused by global warming, for example, we should.  We must.

But it is equally important to recognise that there is much more to do as well, by learning from the experience of today’s devastation to adapt our infrastructure, social systems and commerce to be more resilient to events that we cannot avoid tomorrow.  We owe that to those who are currently feeling the effects of nature’s force this summer.

References

[1] Bureau of Meteorology (2011). Annual Australian Climate Statement 2010 [Accessed 13 January 2011]

http://www.bom.gov.au/announcements/media_releases/climate/change/20110105.shtml

[2] National Climate Centre (2011). An extremely wet December leads to widespread flooding across eastern Australia. Special Climate Statement 24. available at http://www.bom.gov.au/climate/current/special-statements.shtml

[3] For example, Bureau of Meteorology (2011). Known floods in the Brisbane & Bremer River Basin [Accessed 13^th January 2010] http://www.bom.gov.au/hydro/flood/qld/fld_history/brisbane_history.shtml

[4] For example, Bureau of Meteorology (2011). Latest River Heights for Brisbane R at City Gauge #

 [Accessed 17 January 2011] http://reg.bom.gov.au/fwo/IDQ65389/IDQ65389.540198.plt.shtml

[5] Yeo, SW (2002). Flooding in Australia: A review of events in 1998. Natural Hazards, 25, 177-191

[6] Bureau of Meteorology (2010). Climate Education: Floods [Accessed 13^th January 2011] http://www.bom.gov.au/lam/climate/levelthree/c20thc/flood.htm

[7] Bureau of Meteorology (2005). El Niño, La Niña and Australia’s Climate

http://www.bom.gov.au/info/leaflets/nino-nina.pdf

[8] Bureau of Meteorology, 2008. Australian Climate Influence: La Niña, [Accessed 13^th January 2011]

http://www.bom.gov.au/watl/about-weather-and-climate/australian-climate-influences.shtml?bookmark=lanina

[9] Carrè, Matthieu; et al. (2005). “Strong El Niño events during the early Holocene: stable isotope evidence from Peruvian sea shells”. The Holocene 15 (1): 42–7. doi:10.1191/0959683605h1782rp

[10] Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor and H.L. Miller (eds.) Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, 2007. Chapter 3: Observations: Surface and Atmospheric Climate Change http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch3.html 

[11] Australian Academy of Science, 2010. The Science of Climate Change: Questions and Answers.

http://www.science.org.au/reports/climatechange2010.pdf

[12] Jones, R.N. and Preston, B.L., 2006. Climate Change Impacts, Risk and the Benefits of Mitigation, CSIRO, Victoria http://www.csiro.au/files/files/pb9u.pdf