|2011-01-26 14:00:11||Vulnerability: guest blog post requiring feedback|
The Brisbane floods of 1893 and 1974 both resulted from a cyclonic rain depression. This was not the cause of the 2010/11 floods and let us be clear, here we are not just talking about Brisbane or even Queensland floods but to widespread heavy precipitation and flooding which have occurred in Sri Lanka, Southern Africa, Eastern Australia, Brazil and other places.
The cause of these floods has been the build-up of water vapour in the troposphere during the last El Nino, exacerbated by global warming making the build-up much larger than usual. Water vapour is of course the most powerful of greenhouse gases and its build-up contributed to heightening the warming effects of the 2009/10 El Nino and drought conditions in many of the places now affected by floods.
This was followed in mid-2010 by onset of a La Nina, a cooling event which, coming into contact with record build-up of water vapour, has resulted in record precipitation, largely in the southern hemisphere due to the Coriolis effect.
It is self evident that what came down must have initially gone up as water vapour. What made it go up in such volume if not atmospheric warming and if the latter, what caused it if not global warming induced by the greenhouse effect?
Heavy rainfall in December 2010 - January 2011 is not the result of normal interaction between El Nino and La Nina. Were this the case, we should have expected major flooding of the magnitude recently experienced much more frequently but this has not been the case.
The 2010/11 floods point to two things long predicted by climate scientists: 1. Growth in the number and frequency of extreme climate events and: 2. Greater climate sensitivity to increasing temperature than hitherto indicated by climate models. Both are due to an increase in the presence of greenhouse gases in the atmosphere such as water vapour produced by feedback arising from anthropogenic global warming.
A problem facing much of Queensland is that vast areas of the State are now saturated, just before on-set of the wettest period of the year. Cyclonic rain depressions are common from February to April, with potential to produce further rainfall over central and northern parts of Queensland, causing further flooding.
In Australia, we should expect that as global warming continues, extreme climate events such as drought, heat-waves and flooding will occur sooner, become more frequent and increasingly severe, as may the strength of El Nino and La Nina events.
The effect of the floods have been disastrous. They hit the Eastern States of Australia hard, nowhere harder than in Queensland where tragic loss of life has resulted. In that State, they have flooded an area larger than France and Germany combined.
Flooding has damaged over 30,000 homes and thousands of businesses, forced evacuation of small towns, flooded over 50 coal mining operations, killed crops and livestock over a huge area causing food shortages and higher prices, destroyed commodities such as cotton and oil seed crops, cut road and rail links and damaged thousands of kilometers of roads.
Property repairs are likely to cost over $30 billion and full recovery will take years. Economic consequences have yet to be calculated but it is already clear that government expenditure will have to increase at a time when public revenue from mining and associated activities will fall, forcing governments to borrow, impose new taxes and divert expenditure on social programs such as education, health and welfare programs.
What have we learned from this disaster? We should have learned its causes, how vulnerable we are to extreme climate events, the need for action to reduce their occurrence and severity and how difficult and costly it is to protect ourselves from their effects.
An immediate and obvious lesson is not to rebuild on land which is vulnerable to flooding as a result of rainfall or high tides raising river levels but to move to higher ground. Protection against future extreme precipitation events such as those experienced in 2010/11 is very limited, and largely unaffordable.
One measure which can and should be taken is to limit the global warming which is occurring and has been responsible for build-up of water vapour in the atmosphere, resulting in such heavy rainfall. This can be done by reducing anthropogenic greenhouse gas emissions until their concentration is reduced to pre-industrial levels of ~280 ppm.
This is not a measure which can be effectively taken by Australia alone. It requires concerted action by all countries, particularly the top 20 emitters, collectively responsible for over 80 percent of global emissions in 2007.
Australia is the world’s largest exporter of coal and CO2. It needs to consider whether it is cheaper to maintain that position and pay for the consequences of an increasing number of severe climate events or reduce its emission and export of greenhouse gases, develop a lower carbon economy and put itself in a position of being able to demand that other countries do the same.
Defence against flooding is very limited, very expensive and of doubtful effectiveness, particularly in preventing inundation of flood plains such as those on which the cities of Brisbane, Rockhampton and Cairns are built.
The prime cause of the 2010/11 floods was global warming resulting in build-up water vapour in the atmosphere. It should be addressed by adopting and enforcing measures to reduce greenhouse gas emissions. In the event that such action is not taken, it should be accepted that events of the kind experienced in 2010/11, as well as longer drought and higher temperature will re-occur with increasing frequency, severity and cost.
Scientists and economists have both pointed out that prevention is better than cure and a lot cheaper.
"The prime cause of the 2010/11 floods was global warming resulting in build-up water vapour in the atmosphere." This is a very strong statement, quite a bit stronger than what we said in the recent newspaper article.
How close to the edge are we on this one?
Cool, heightening awareness of extreme events with global warming is one way where we can make inroads into public perception. If we can propagate that message (accurately) we can turn this ship around (he types with fingers crossed!).
Having said that, I think this post crosses over the line in a couple of areas. One already pointed out by Neal, and this sentence:
"The cause of these floods has been the build-up of water vapour in the troposphere during the last El Nino, exacerbated by global warming making the build-up much larger than usual"
I don't know that the"cause" has been El-Nino. Water vapor having a residence time measured in days, doesn't make that a viable proposition. It's the global warming (& ocean heat) that is driving this. The whole El Nino-La Nina warm/cool thing is irrelevant. Despite La Nina being a "globally" cool phenomenon, it causes a lot of warming around Australia & NZ (speaking from experience past & current). The huge floods in Sri Lanka, the Philippines & Brazil too were exacerbated by extremely warm SST's. The next strong El-Nino will just shift the locations of freak flooding.
And let's not forget, the long-term outlook for much of Australia is drought. Horrendous & tragic flooding associated with global warming enhanced La-Nina won't change that.
Don't mean to be a drag man!. I just don't want our words to be "legitimately" used against us in the future, if we make claims that are unsupportable. Still think we can get the message across without exaggeration.
|2011-01-26 22:32:59||More comments|
Apologies but I do have some concerns over some parts of the text. You correctly draw the connection between global warming and the trend in more frequent heavy downpours. But you also directly attribute the cause of a single weather event with climate change. As far as I'm aware, there is no peer reviewed research that does that. Specific comments:
"What made it go up in such volume if not atmospheric warming and if the latter, what caused it if not global warming induced by the greenhouse effect?" - one possible explanation is that El Nino transitioned very quickly to La Nina, faster than usual, so the La Nina was able to push more moist air towards Australia than usual. I don't know if that's the case, there is still study into this currently underway, but the point is it's dangerous to ascribe climate change to a single weather event when there might be specific weather reasons.
"Greater climate sensitivity to increasing temperature than hitherto indicated by climate models" - how does a single flood or series of floods prove higher climate sensitivity? Do you mean warming leads to more water vapor which changes cloud cover which is a positive feedback? If so, there is some evidence for this (Dessler 2010) but it's a matter of uncertainty - Dessler's evidence for positive feedback is not yet statistically significant. Seems a shaky statement.
"The prime cause of the 2010/11 floods was global warming resulting in build-up water vapour in the atmosphere" - I have to disagree with this statement. My understanding is La Nina is the prime cause. Global warming either made it worse and/or increased the likelihood of the heavy downpours.
Generally, this article is great and does well in drawing attention to the significance of climate change in regard to floods. But beware of overstating the state of the science - you can undermine your central message with a single false statement, as the FEU debacle taught us.
I agree with the previous comments and I would add that we should back up all our assertions with references, peer-reviewed where possible, or pronouncements by recognised academic or research organizations, or non-reviewed comments by established experts in the field. As bloggers, some of us anonymous, we can't expect our readers to treat us as authorities.
I didn't understand the latter part of this sentence: This was followed in mid-2010 by onset of a La Nina, a cooling event which, coming into contact with record build-up of water vapour, has resulted in record precipitation, largely in the southern hemisphere due to the Coriolis effect.
The Coriolis effect makes objects travelling away from the Equator veer to the east and vice versa. It's not clear to me why this should result in relatively more precipitation in the S Hemisphere.
Having said that, I think that a subject like this is ideal for Skeptical Science but it needs more careful wording, more admission of uncertainty as to the attribution of the floods to AGW, and more references to or quotes from credible authorities.
|Thank you for your comments, all of which are accepted and will be taken into account during re-write.|