The Earth’s dynamics are complex and interrelated. For example, the chemical composition of magma below volcanoes in Indonesia has historically been linked to crop failures in Europe! This example from the eruption of Mount Tambora in 1815, where it is thought that temperatures caused the “the Year without a summer”. Meronen et al (2012) demonstrated that the gasses (such as sulphur dioxide) released from volcanic eruptions will have severe impacts on weather systems. These weather impacts include temperature but are also likely to cause other impacts either directly or indirectly, particularly precipitation resulting in major floods, particularly in Europe (Fagan 2000); though elsewhere there were flooding events that are apparently correlated. These floods often caused catastrophic damage.
Recently, of course, many many people have been affected in some way by, in some places, the worst floods recorded since, well, records have been documented in Australia. I've seen a few explanations of the "why" including the following three main ones:
• On social media I’ve seen the flooding attributed to the practice of “cloud seeding”,
• I’ve also seen in the broader media the flooding attributed solely to anthropogenic climate change.
• The Bureau of Meterology lies the blame squarely on La Nina.
I’ll address all of the above and raise a hypothesis which is different, but in some way related to all of them.
Cloud seeding (introducing chemicals or particles into the atmosphere to encourage water droplets to form or increase in size) is sometimes recognised a as mechanism to increase the chance of rainfall. It is worth noting though, that statistically it is very difficult to prove that cloud seeding does much at all. The technique (if it can be called that), is applied mainly at dry times on the ground but when there is moderate atmospheric water content. Cloud seeding was tested in South East Queensland during the desperately bad drought from 2006 (Tessendorf et al 2012), though it was not possible to determine if clouds were formed due to the seeding material, or simply due to natural updrafts of air (one of the ways that clouds are formed naturally). I can find no record that cloud seeding took place in eastern Australia preceding the weather event, but it is worth noting that the volume/mass of seeding material needed would rule out seeding as causing the huge scale of rainfall.
The second reason I outlined above, is anthropogenic climate change. It is unfortunate that this has been attributed as a cause by many public figures and organisations, because it is impossible to attribute a single weather event to a climatic situation. Climate is a statistical representation of longer-term weather patterns and so one weather event does not demonstrate the climate, or a climate change. I will also note that if climate change was a factor in this weather event it is different from observed extreme weather events in Australia, where over the last several decades the incidence and frequency of storms and floods has decreased. Even models of storm frequency shows a decrease in frequency and a higher rate of break up of storms before impacting on the Australian landmass due to anthropogenic climate change (e.g. Abbs 2012). So, I have trouble pinning this flood event on anthropogenic climate change, or even natural climate change.
The third reason outlined seems to be the most likely of the three listed, and indeed I cannot argue with it much, except to potentially add a geological factor. Yes, you guessed it, volcanic eruptions. On the 15th of January this year, there was an extreme eruption of the Hunga Tonga –Hunga Ha'apai volcano. On facebook I re-posted a video, that demonstrated the scale of the eruption. The immediate particulates and aerosols (including sulphur dioxide) generated by the eruption past through the atmosphere across northern Queensland in the next several days. This material continued to circulate in various levels in the atmosphere over the subsequent weeks. So, a hypothesis is that if you combine the increased air moisture as a result of Coral Sea water temperature during this El Nina weather pattern we are in, combined with the blocking high pressure system in southern Australia (a common Australian summer climatic feature), with the natural effect of a huge volume of natural “cloud seeding” sourced from the volcanic eruption, this may have resulted in the extreme rainfall in eastern Australia. This would reflect the historical impacts on weather and floods resulting from volcanic events elsewhere in the world over recorded history, and reasonable enough that I think it worth considering.
Of course, speculation as to the “why” does not help those who have been so adversely affected (even killed) during the floods, but having some idea as to “why” can help us plan for future weather events. As a former Lismore resident, my thoughts go out to those in Lismore as well as those further up and down the coastal strip who are still living through the damage of the floods.
For some old posts on how volcanic eruptions from the Tonga area can affect the beaches of our coastline click here:
Pacific Islands on Holiday to the North Coast
Tonga Comes to Visit Again
References/bibliography:
*Abbs, D. (2012). The impact of climate change on the climatology of tropical cyclones in the Australia region. CSIRO Climate Adaptation Flagship Working paper No.11.
*Fagan, B (2000) The little Ice Age: How Climate Made History, 1300-1850, Basic Books, New York.
*Meronen, H. et al (2012) Climate effects of northern hemisphere volcanic eruptions in an Earth System Model, Atmospheric Research, pp107-118.
*Tessendorf, S.A. et al (2012) The Queensland Cloud Seeding Research Program, American Meteorological Society, vol 93: issue 1.
