Via email from Tom Wigley (climate scientist) with a request to post here:
"Comment on 1000-yr return period. Roger Pielke makes some interesting points. For scientific background on this issue, including examples of how one can usefully employ the return period concept, see my 2009 paper in Climatic Change, 97(1-2), 67-76, “The effect of changing climate on the frequency of absolute extreme events.” This paper is a low level exposition on extremes, return periods, risk, and related ideas. It was originally written in 1988, but is still (even today, 2023) relevant.
First paragraph:
" In some areas of climate impact analysis, the possible impact of a changing mean climate has been dismissed by some writers either because of a belief that society can adapt to a slowly changing mean and/or because expected rates of future changes lie within or not far outside those experienced in the past. The two standard counter arguments to this optimistic view are: (1) the future will lead to much longer periods of protracted change in one direction, with final conditions well into the no-analogue region; and/or (2) the main impacts will accrue through changes in the frequency of extremes. In the literature on greenhouse effect, lip service is often paid to the effect of changes in the frequency of extremes. But just how will a slowly changing mean affect the frequency of extremes? Quantitative discussions of this subject are rare."
As an engineering design tool the N year event has proven to be resilient. However few understand the concept and it is subject to misuse. As a communication tool for conveying risk it's easily exploited for political or careerist advantage.
In my industry (water utilities) we talk about design to prevent statisiclally rare(ish) events; 1 in 200 or 500 yr drought event protection or 1 in 40yr flood event protection. Both have volume and time dimensions. I wholly accept it is a difficult concept to explain to the public and I've toyed with a few others that might help; e.g. tossing a 2 sides coin does not mean you will always get a different answer each time. (In the long run the answer will alternate (regress?) to the mean but any run of answers will be very different.
If we retire the concept, what shall we replace it with? Is there another concept which better conveys the truth which doesn't require a relatively advanced understanding of statistics? I wonder what the probability is that a layperson coming in cold would read this article with sufficient concentration to grasp its meaning in much depth. I'm sure that the USGS definition requires considerable background training to understand. And even then there is the question of how to understand the way the statistics is used, which is tendentious 90% of the time, even if it is used pragmatically e.g. for insurance purposes. I would prefer sticking with the concept AND more often producing articles like this so that there may be more understanding not just of this issue, but statistics in general.
The execrable Mann once again does his thing, i have read several such critiques of it but zero in main stream media, which as always is narrative control. They just ignore what we are saying here.
Because it doesn't fit the narrative.
In calgary we had a big flood in 2013 which the usual suspects instantly termed a "500 year flood". Except later that year a paper from the U of C showed that 2013 was only the 5th worst flooding in the Bow River basin in the previous 130 years.
oops.
Searching but have not found it yet, i read about it in the calgary Herald.
I'm a gardener and so i have a rain gage and i keep track of rain to an extent.
The 2005 flood was called a 100 year event while 2013 was called 500 year, but in 2005 i registered 17" of rain in June whereas in 2013 i saw 9".
So its all about where and how fast, completely random.
They simply don't care about corrections like the one you provide here, they need the extinction click bait and Mann is happy to provide it
To extend your explanation, a 1000 year event is defined for a specific area. If there are 1000 such areas in the country then an event could be expected every year. Would provide plenty of fodder for hysteria.
Roger, I would bet money that the "decorated climate scientist" knows the real meaning. He is just using exaggeration and obfuscation to push his politics. You're too polite.
The concept should be retired only if, and I can see that condition is being realised, the damage it does is getting too much.
This is another problem of 'thinking slow and fast' a la Daniel Kahneman; people see a time reference and shut down part of their slow mental process which would help them to realise that time has nothing to do here.
In fact, terms such as 1 in 1000 year flood are descriptors of SIZE, and not occurrence. It is not bogus or irrelevant or useless. The concept was not meant to be used except for design purposes and as a measure of size and unlikelihood.
Having worked in water resources planning for several decades, I couldn't agree more with your conclusions!! "N-year" events are useful in providing a risk framework, but too often misleading to the lay person on the city council or county board.
While we're correcting terminology, could we eliminate the phrase "climate-related deaths." Climate is defined as an average, and I don't know of any average that actually killed someone. "Weather-related deaths" would be far more accurate and less ominous in tone.
Terrific explanation. I intuitively knew the N-year convention was bogus but hadn't tried to suss it out. You have done it and I sure as heck could not have.
"This week I watched one of the world’s most visible climate scientists, Michael E. Mann, go on national TV and in process show that he had no idea what the concept actually means."
After many years as an environmental scientist, I knew the definition of science had changed when I saw the emotional defense of Michael Mann's work back in the day. Things have only gotten more interesting in the intervening years.
I tried to animate the concept several years ago.
http://polistrasmill.blogspot.com/2012/11/non-random-thoughts-about-random.html
Via email from Tom Wigley (climate scientist) with a request to post here:
"Comment on 1000-yr return period. Roger Pielke makes some interesting points. For scientific background on this issue, including examples of how one can usefully employ the return period concept, see my 2009 paper in Climatic Change, 97(1-2), 67-76, “The effect of changing climate on the frequency of absolute extreme events.” This paper is a low level exposition on extremes, return periods, risk, and related ideas. It was originally written in 1988, but is still (even today, 2023) relevant.
First paragraph:
" In some areas of climate impact analysis, the possible impact of a changing mean climate has been dismissed by some writers either because of a belief that society can adapt to a slowly changing mean and/or because expected rates of future changes lie within or not far outside those experienced in the past. The two standard counter arguments to this optimistic view are: (1) the future will lead to much longer periods of protracted change in one direction, with final conditions well into the no-analogue region; and/or (2) the main impacts will accrue through changes in the frequency of extremes. In the literature on greenhouse effect, lip service is often paid to the effect of changes in the frequency of extremes. But just how will a slowly changing mean affect the frequency of extremes? Quantitative discussions of this subject are rare."
As an engineering design tool the N year event has proven to be resilient. However few understand the concept and it is subject to misuse. As a communication tool for conveying risk it's easily exploited for political or careerist advantage.
In my industry (water utilities) we talk about design to prevent statisiclally rare(ish) events; 1 in 200 or 500 yr drought event protection or 1 in 40yr flood event protection. Both have volume and time dimensions. I wholly accept it is a difficult concept to explain to the public and I've toyed with a few others that might help; e.g. tossing a 2 sides coin does not mean you will always get a different answer each time. (In the long run the answer will alternate (regress?) to the mean but any run of answers will be very different.
Personally, I find mean repeat interval a more useful concept. It also changes but over time the sample mean approaches the true mean.
PS. Many of us think of Michael Mann as Judith Curry's Evil Twin!
If we retire the concept, what shall we replace it with? Is there another concept which better conveys the truth which doesn't require a relatively advanced understanding of statistics? I wonder what the probability is that a layperson coming in cold would read this article with sufficient concentration to grasp its meaning in much depth. I'm sure that the USGS definition requires considerable background training to understand. And even then there is the question of how to understand the way the statistics is used, which is tendentious 90% of the time, even if it is used pragmatically e.g. for insurance purposes. I would prefer sticking with the concept AND more often producing articles like this so that there may be more understanding not just of this issue, but statistics in general.
The execrable Mann once again does his thing, i have read several such critiques of it but zero in main stream media, which as always is narrative control. They just ignore what we are saying here.
Because it doesn't fit the narrative.
In calgary we had a big flood in 2013 which the usual suspects instantly termed a "500 year flood". Except later that year a paper from the U of C showed that 2013 was only the 5th worst flooding in the Bow River basin in the previous 130 years.
oops.
Searching but have not found it yet, i read about it in the calgary Herald.
I'm a gardener and so i have a rain gage and i keep track of rain to an extent.
The 2005 flood was called a 100 year event while 2013 was called 500 year, but in 2005 i registered 17" of rain in June whereas in 2013 i saw 9".
So its all about where and how fast, completely random.
They simply don't care about corrections like the one you provide here, they need the extinction click bait and Mann is happy to provide it
To extend your explanation, a 1000 year event is defined for a specific area. If there are 1000 such areas in the country then an event could be expected every year. Would provide plenty of fodder for hysteria.
I realise that; it is one of many uses outside engineering, but if it is used to mean anything more than size, then it is being used in error.
Roger, I would bet money that the "decorated climate scientist" knows the real meaning. He is just using exaggeration and obfuscation to push his politics. You're too polite.
The concept should be retired only if, and I can see that condition is being realised, the damage it does is getting too much.
This is another problem of 'thinking slow and fast' a la Daniel Kahneman; people see a time reference and shut down part of their slow mental process which would help them to realise that time has nothing to do here.
In fact, terms such as 1 in 1000 year flood are descriptors of SIZE, and not occurrence. It is not bogus or irrelevant or useless. The concept was not meant to be used except for design purposes and as a measure of size and unlikelihood.
Love when you show up Mann.
Having worked in water resources planning for several decades, I couldn't agree more with your conclusions!! "N-year" events are useful in providing a risk framework, but too often misleading to the lay person on the city council or county board.
While we're correcting terminology, could we eliminate the phrase "climate-related deaths." Climate is defined as an average, and I don't know of any average that actually killed someone. "Weather-related deaths" would be far more accurate and less ominous in tone.
More grist for your mill, sir.
Terrific explanation. I intuitively knew the N-year convention was bogus but hadn't tried to suss it out. You have done it and I sure as heck could not have.
"This week I watched one of the world’s most visible climate scientists, Michael E. Mann, go on national TV and in process show that he had no idea what the concept actually means."
After many years as an environmental scientist, I knew the definition of science had changed when I saw the emotional defense of Michael Mann's work back in the day. Things have only gotten more interesting in the intervening years.