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Perils and Pitfalls of Event Attribution

By: Dr. Ricky Rood , 6:37 PM GMT on March 11, 2011

Perils and Pitfalls of Event Attribution

Some of you may have noticed a story that originated in the Green Blog by John Rudolf on the New York Times website (March 9, 2011) about the Russian heat wave in the summer of 2010. The news story reports on a paper to appear in Geophysical Research Letters by Randy Dole and co-authors who conclude that in the historical record there is evidence of similar events of comparable intensity. It follows, they argue, that the Russian heat wave cannot be attributed to climate change – rather it is a very rare event. (Paper at GRL website, NOAA Description of Dole et al. article, Jeff Masters blog and analysis) For a variety of reasons I followed how this story propagated around the blogs and news services for the next 24 hours. It was picked up by many sites including, quickly, by the (according to comment writers on this blog) mysterious Steven Goddard (any more on that story?).

As it happens, I am writing an article for Earthzine with Christine Shearer on how scientists and the media engage each other about extreme events (Shearer blog on WU). When it is ready, I will proudly announce it and provide a link. That article will focus on a sociological analysis of extreme weather and the media. This blog will touch on a couple of the issues we raise in that article, but mostly it will be a scientist's point of view on the discussion of the value of pursuing the attribution of single events to climate change in a context largely described by public discourse.

Event Attribution: A public question that arises after every new extreme event is: can this event be attributed to climate change? At this point in time, I cannot imagine the answer to that question ever being, convincingly, yes. Scientists often rely on the statement: no single event can be attributed to climate change, but this event is not inconsistent with climate change. I have used that answer; perhaps, I repeat the mantra (Pakistan: A Climate Disaster Case Study). On thinking about that answer, it is more than useless. But then thinking about the question, it is, depending on your point of view: a natural question, a naïve question, an ill-posed question, or a leading question.

Why do I say that I cannot imagine the answer to such an event attribution question being convincingly yes?

Dole et al. study attribution, and they do it magnificently. Their strategy is to do a physical, statistical, and process analysis of historical information. If they find like events in the historical data, then that makes it impossible to attribute the event, wholly and solely, to climate change. This implies an odd metric: an event that is “caused” by climate change must be different than any event that has been previously measured. Do we have to have some Day After Tomorrow event where physical principles are suspended and the world moves to a whole new set of behavior?

The probability that looking through all of the observations, all of the history, that you are going to find a “like event” is high. I say “like event,” because there will be some differences no matter what. Of course, it has been hot in Moscow before, so there is some atmospheric pattern that yields “hot in Moscow.” We find like events and then, maybe, the current event is 10 degrees hotter and two weeks longer; it’s a obvious record. But is it climate change?

More likely than a obvious record, there will be another event that is similar, about the same, but not quite. Then it becomes the same question as, was Henry Aaron better than Babe Ruth? Aaron hit more home runs, but there are lots of other differences that experts point to and argue about: length of season, quality of pitching, … . Throw in Barry Bonds and Mark MacGwire; they hit a lot of home runs. Well maybe the physics (or physiology) of Bonds and MacGwire are different? Is climate change weather on steroids?

Suppose you look through the record and find that the current event is 10 degrees warmer and 2 weeks longer. Is it climate change? Do you know whether or not that if you had just one more year of observations, that you would not find out that that next year had a similar hot period. What about similar events in the medieval warm period? The data system was relatively sparse 100 years ago; maybe we just missed the event. So even if we find an event that is more intense, more persistent, then we have the problem - have we really observed the historical extremes? Have we observed all natural variability? This will always challenge the public and political discourse on event attribution - always.

More likely than finding an event that is extraordinarily different, we find an event that’s about the same length of time, but one degree warmer. Is the thermometer good enough? Are the instrument sites good - have they changed? What about the urban heat island? What about regional water management projects? Good scientific investigation and analysis can account for these issues, but in any event they are sources of differences, which as in the Aaron versus Ruth argument, are irreducible. Perhaps an extreme record can be established, but then, would that be climate change?

It is hard to see how playing the game of defining extreme events and then attributing that event to “climate change” can ever be won. It is often possible to isolate with statistical certainty descriptions that the emissions of greenhouse gases have influenced an event, but that represents one of those paths of nuanced explanation. Such nuanced explanation, again, assures there is not a definitive "yes" in the public and political discourse. In fact, it seems like it is a game that necessarily leads to controversy, and controversy is the fuel of talk radio, blogs propagating around the world, and the maintenance of doubt.

But what about that question of attribution? Let’s say you find an event that is rare, that is extreme, but not a new record - does that really say that the event today, right now, is not climate change?

In a very basic, old fashioned way, weather and climate are different descriptions of the same thing. They depend on how we, somewhat arbitrarily, define how we want to organize the observations. Crudely, we average weather to make climate. Since we work from the premise that climate change will be slow, for the most part the same type of weather events will make up the old (natural) climate and the new (changed) climate. Over time, the frequency of events will change, what were rare events in the old climate, might just be less rare events in the new climate. I pose, however, that even in a world that is on average four degrees warmer than today, there will be a seventy two degree, sunny day in the spring in Washington D.C. Do we then march through the days 50 years from now and say, “old climate,” “new climate?” The idea of isolating a single event on a single day or a persistent event and asking if it is caused by climate change – does that make sense? Is it even meaningful given the definition of climate? How did we arrive at the question of climate change being a causative of a weather event?

I want to restate the previous paragraph in a different way. Let’s assume that climate is averaged weather. Then climate is defined by a mean, a standard deviation, and a set of more sophisticated parameters that describe statistical distributions. What we have come to call the natural climate is defined by certain values of the mean and measures of deviations from the mean. The future, changed, warmer climate will have different values of the mean and the measures of deviations. With the presumption that the warming of the climate is incremental, then the majority of the events in the warmer climate will be like the events in the “natural” climate. Therefore, just because a like event existed in the "natural" climate does not mean that the current event is not part of the "changed" climate. There are NOT two climates - a natural one and a changed one - with our job being to determine if we have flipped from one to another. When we say that there will be more extreme events in the changed climate, it does not necessarily mean there will be a relentless unwavering string of records. There will, perhaps, be more events that have been previously rare. But, it is not climate change causing weather events.

As you study climate change, it becomes clear that talking about independent isolated events is not especially productive when trying to address attribution questions. Climate is an average, or perhaps better, an accumulation of weather events. As such it is important to consider how a large number of events act in concert, in correlation, in cohesion.

One other point that I want to make: The practice of isolating a single event and attributing that event to climate change, is one of the most effective ways of opening up scientific investigation to effective scientific criticism. (see Pielke, Sr. et al. 2007) A single-event attribution claim is an open and appropriate invitation to those with knowledge of or interest in local information to investigate the attribution claim. Almost inevitably this leads to identification of more sources of uncertainty, which like the Aaron versus Ruth argument, are irreducible. This necessarily contributes to controversy, and controversy is the fuel of talk radio, blogs propagating around the world, and the maintenance of doubt.

This entire process of event attribution is one place where scientific investigation of the climate interfaces with the media. Therefore, it is also a place where, by definition, scientific investigation interfaces with the political argument. My analysis above suggests that, as framed by the public discourse, the pursuit of the path of event attribution and the explicit or implicit linkage of that attribution to climate change is scientifically questionable. This stands in contrast to the scientific pursuit of extreme events in historical context and the evaluation of whether their frequency of occurrence is changing. Politically or in terms of informing the public, the primary product of the pursuit of event attribution is to build and maintain doubt. The exception to doubt maintenance would be if a definitive, metaphorical smoking gun was discovered. But what is the probability of such a smoking gun being discovered in this process? A different perspective is needed on the role of extreme events in climate and the attribution of such events to global warming. As climate scientists, we have to think about what these studies mean to the body of our field’s communication of climate change.


And here is

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Reader Comments

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406. iceagecoming
4:16 AM GMT on March 26, 2011
Quoting cyclonebuster:
Ya'll get it yet?

I am starting to like it more and more.
Still partial to dark energy for the long run.

Endless Universe: Beyond the Big Bang

Member Since: December 31, 1969 Posts: Comments:
405. iceagecoming
3:10 AM GMT on March 26, 2011
Concerning but not replying to № 390
(would not want to ruffle any feathers)

Fossil DNA Proves Greenland Once Had Lush Forests; Ice Sheet Is Surprisingly Stable

Climate theories over-turned

The research results are the first direct proof that there was forest in southern Greenland. Furthermore Willerslev found genetic traces of insects such as butterflies, moths, flies and beetles. But when was that? According to most scientific theories to date, all of southern Greenland and most of the northern part were ice-free during the last interglacial period 125,000 years ago, when the climate was 5 degrees warmer than the interglacial period we currently live in.

This theory however, was not confirmed by Willerslev and co-workers subsequent datings. He analysed the insects' mitochondria, which are special genomes that change with time and like a clock can be used to date the DNA. He also analysed their amino acids which also change over time. Both datings showed that the insects were at least 450,000 years old.


Oh, it got warm before AGW, must be some evil energy
company plot to sway science. AHHHHH
Member Since: December 31, 1969 Posts: Comments:
402. sirmaelstrom
1:13 AM GMT on March 26, 2011
Quoting cyclonebuster:

Calculate how many gigatonnes of cold water flow through the tunnels per year if needed while at the same time producing electrical power?

LOL. Given our past discussions on the subject, I wouldn't know where to begin. If I recall, you've done a lot of calculations on the subject. Anyway, I would think your next course of action would be to get someone to finance building a working small scale prototype to demonstrate that they can do what you say they can: produce energy and regulate SSTs. I have no idea what the specifics would be. I do recall the Youtube videos you posted, but I don't think that a few yards of PVC pipe and dye are going to be enough to convince anyone.

Edited for grammar/wording.

Added: I'm out for a bit...I may check back later tonight.
Member Since: December 31, 1969 Posts: Comments:
399. sirmaelstrom
1:03 AM GMT on March 26, 2011
Concerning but not replying to № 390:

I don't think I can be fairly accused of trying to select "conservative" estimates here as I took the estimates from a Skeptical Science post from February 2011. Perhaps the site is somewhat more conservative than Climate Progress though.

Anyway, my first question is whether the Petermann event is calculated within the 540 cu km value; if it is then it should be noted that an event such as the Petermann one will greatly skew the average for the year. The Petermann event wasn't really that unusual. Of course the value is specified as be "inland ice" so maybe it's not being included.

My next point would be that this is only a one-year observation. Also, as the graph from Skeptical Science notes, there are several estimates that have been done within the past five years, several that have been done concurrently. I'm not sure that simply because a study was concluded/published later it necessarily "refutes" all earlier studies. In particular the study with the lowest estimate alleged that previous measurements were overestimated due to incorrect/insufficient corrections for rebound of crust under melting ice. Unless subsequent studies addressed this I can't really see how the previous study in necessarily "refuted". More than likely, the spread in estimates is likely indicative of the uncertainty and difficulty in measuring the ice melt.

* * *

As far as the perceived censorship: I have no idea by what process the post was removed--I didn't flag or minus it myself--but I can see why Admin might do it. All the post did was complain that there were twenty posts or so that MichaelSTL couldn't see because he had ignored them. He seemed to be suggesting that people that he has ignored don't have a right to comment, which is a bit inflammatory and would just lead to argumentative responses. If he's going to "Ignore" people, he should perhaps actually ignore them.
Member Since: December 31, 1969 Posts: Comments:
397. sirmaelstrom
12:26 AM GMT on March 26, 2011
№ 388
Quoting weatherboy1992:
Algebra equation. Given a volume of 3 million cubic kilometers, an ice lose in 2010 of 200 cubic kilometers, and an annual acceleration of 20 cubic kilometers a year, solve for the year the Greenland ice sheet disappears!

From a strictly mathematical standpoint...

mass=3000000-melt; where melt=integral(200+20t)

This yields melt=200t-10t² and mass=3000000-200t-10t²

I am going to solve it the lazy way (LOL):

Graphing m=3000000-200t-10t² below:

See here.

Looks like just under 540 years. Setting m=0 and solving for t yield about 537.814 years.

* * *

Now, from a practical standpoint, it's a stretch to assume that the rate of acceleration of melt will be over the next 500 years, especially considering the short periods of observation. Note also that near the end of the 500 year period, ice would have to be melting at over 10,000 gigatons per year to keep up with the graph. Values such those do not seem realistic.

Member Since: December 31, 1969 Posts: Comments:
385. sirmaelstrom
2:12 AM GMT on March 25, 2011
Quoting weatherboy1992:
That was helpful, thanks sirmaelstrom.

You're welcome.
Member Since: December 31, 1969 Posts: Comments:
383. sirmaelstrom
1:20 AM GMT on March 25, 2011
№ 380

Well...I'm not MichaelSTL but I'll take it...

According to data gleaned from the following two links:

http://www.skepticalscience.com/Various-estimates -of-Greenland-ice-loss.html

Pretty wide spread of estimates and significant uncertainties in the long-term, with most having short observation times of 5-10 years, as can be seen in the graph below:

The most recent estimates (the last five years or so) give estimates of about 110 to 290 Gt (Gigatons) per year, or given the total ice sheet mass of about 3 million Gt, between 0.004-0.01% mass loss per year.

I would say long-term acceleration is also somewhat uncertain since it relies on very short observation intervals as well--especially the GRACE gravity estimate--but here is a graph from the Skeptical Science link:

Acceleration results are given in the graph; the corresponding percentages are about 0.0007 ± 0.00003%/yr for the mass balance method, and 0.0006 ± 0.0003%/yr for the gravity method.

I hope I was helpful.
Member Since: December 31, 1969 Posts: Comments:
379. iceagecoming
5:21 PM GMT on March 24, 2011

Climate Change Likely Caused Polar Bear to Evolve Quickly

Climactic changes might currently be threatening the survival of polar bears (Ursus maritimus), but similar shifts appear to have played an important part in bringing the species into existence in the not too distant past.

Researchers announced today that they have sequenced the mitochondrial genome of an ancient polar bear. The genetic traces they found in the bear's 110,000- to 130,000-year-old jawbone reveal that the species likely split from brown bears (U. arctos) just 150,000 years ago, at a time when specializing in arctic living quickly became an advantage rather than a liability.

The species' rapid evolution sheds new light on one of the emblematic species of climate change. Although the breed has become a popular flagship species for the issue, scientists knew little about how past climate affected the bear's evolutionary success.


Well, looks like climate change created a new bear,
just like the end of the last glaciation removed
the mega fauna from Northern Hemisphere.

Just listened to a NPR story on Curt Stager on how
we may have helped that extinction. And that Lake
Champlain does not ice over anymore. Really, these
Paleoclimategeologistpeerreviewed Dr's need to get out of the classroom a little more frequently.


And they claim he was a climate warming sceptic.



I do appreciate all the modern technology that allows
me to poke holes in all these issues.
It is liberating.
Member Since: December 31, 1969 Posts: Comments:

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Dr. Ricky Rood's Climate Change Blog

About RickyRood

I'm a professor at U Michigan and lead a course on climate change problem solving. These articles often come from and contribute to the course.

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