Tuesday, September 15, 2009

Good science, wrong answer

Sometimes it happens that somebody does good science, but has arrived at a wrong answer. Since most of us think that the answer has to be right (and I'll agree that it's better when it is), this will take some explaining. Let's go back to what science is about -- trying to understand the universe in ways that can be shared. Good science, then, is something that leads to us understanding more about the universe.

For my illustration, I'll go back to something now less controversial than climate. In the 1980s, paleontologists David Raup and J. J. Sepkoski advanced the idea that mass extinctions, such as the one that clobbered the dinosaurs, were periodic. Approximately every 26 million years, for the last about 250 million years, they observed a spike in the extinction rate. Not all were as large as the one that got the dinosaurs.

It so happened that they were at the University of Chicago, in the Department of Geophysical Sciences, and so was I. Further, I was working with time series for my master's thesis. So I asked them about working with their data and seeing what I would find with my very different approach. They were gracious and spent some time explaining what I was looking at, knowing that I didn't think they were right. By my approach, indeed, their idea did not stand. My approach, however, was not a strong one, being susceptible to some important errors. So I never published about it. Still, along the way, I learned more both about time series, and about paleontological data. So that's a plus making the periodic extinction idea 'good science' -- I, at least, learned more about the universe, even if not enough to make original contribution.

One mark of good science is that it prompts further research. Raup and Sepkoski, in their original paper, had made a reasonable case. 'reasonable' being that it could not be shot down by any simple means. 'simple' meaning that the answer was already in the scientific literature. So to knock down the case, itself a normal process in science, the critics had to do some research to show how weaknesses or errors in one or more of the following lead to the erroneous conclusion:
* The statistical methods
* The geological time scale
* The paleontological data (extinction figures, and their dating)

The idea was not sensitive to the geological time scale used, so that fell away fairly quickly. The statistical methods did develop a longer-lasting discussion -- new ones devleoped, flaws in the new and the old methods described (and then discussion about whether the claimed flaws were real).

Most interesting to me, and I think where the greatest good for the science was, was going back to the data. In saying that the extinctions were periodic, one carried the image of something crashing into the earth (like the meteor that did in the dinosaurs) and killing off huge numbers of species (and genera, and families) very quickly. One of the data problems, then, was getting accurate dates for the time of extinction. Often the data could only say that the things went extinct sometime within a several million year window. That's a problem, as then your view of whether it was periodic could depend on whether you put the date of extinction at one end of the geological period or another. So people went to work on getting better dates for when the species went extinct.

Also, I noted above that the original idea applied to the last 250 million years. The reason was, when they started that was as far back as you could go with reasonable data. So work also went in to trying to push back the period of reasonable data.

I don't know what the field ultimately concluded about the idea. I do know that the work to advance or refute the idea resulted in more data about when species went extinct, and better dates for when they did. Further, those newer and better data are themselves useful for learning more about the universe -- there's more to be gained than just answering the original question about whether mass extinctions were periodic.

So, not only did the original publication result in more being learned about the universe, but it was in a way that enables even more learning to happen. That makes it good science. The original idea might have been wrong, but it definitely was good science.

I've focused on the side of scientific merit here. There was a lot of, well, unprofessional, response as well. You can read about both parts in The Nemesis Affair: A Story of the Death of Dinosaurs and the Ways of Science by David Raup. Part of it was because the idea that any mass extinction had to do with things crashing in to the earth was still new, and still widely not accepted. Then this idea comes up and says that not only does it happen (bad enough) but it had happened many times, and happens regularly.

11 comments:

Jesús said...

I tend to think that science is not the answer that you get, but the (scientific) method by which you reached that answer. That's why I've always thought of Arrhenius' climate sensitivity as the right answer (4ºC, well within the current uncertainty range) but the wrong science (overestimated sensitivity with infraestimated emissions). But, in the light of this article, at least he fostered further and crucial research! What would you say?

This is a bit off topic (paleontology remind me of it), so I'll understand if there's no room for an answer ;-):
1) do you know if the expected warming can be described as rapid or even abrupt compared to paleoclimatological precedents?
2) I heard that climate change has been suggested as a cause for events of mass extinction, but in general those are cooling events. Do you know if there is any warming event suggested as a cause of mass extinctions?

Thanks!

Hank Roberts said...

For a contrast with the scientists' approach, look at the Chicago economists, then and now, also contending with a history of repeated disasters:
http://krugman.blogs.nytimes.com/2009/09/14/freshwater-rage/

Hank Roberts said...

Jesús --

--
PETM for one; and see
http://www.google.com/search?q="Peter+Ward"+"Green+sky"

-- http://scholar.google.com/scholar?sourceid=Mozilla-search&q=%22global+warming%22+%22rate+of+change%22

Penguindreams said...

Jesus: To translate Hank slightly -- the Paleocene-Eocene Thermal Maximum. That's about 56 million years ago. I'm not sure, though, that it counts as one of the mass extinctions. Of course deciding which are the 'mass' extinctions is a debatable matter.

Arrhenius is partly a good example. The 'overestimate' involved, though, was that he was incorporating both CO2 and Water Vapor. But not so separately as we would today -- the measurements he worked with combined both effects.

The two most massive mass extinctions are the end-Permian and the end-Cretaceous. Both were cooling periods. Both had massive vulcanism, and both had large impact events.

Hank: Krugman's earlier magazine article pointed to a crucial point -- the 'freshwater schools' of economics, Chicago being one, had left observables for elegant mathematical theories. In climate, our equivalent would be the folks, say, who 'proved' that summer is not warmer than winter, or the recurring 'proofs' that there is no greenhouse effect. The mathematics might be correct, but they're not grounded in observation.

Jesús said...

Thanx for the explanations!

PS. I couldn't find a paleoclimatological perspective on the rate of change in GoogleScholar, but no problem ;) )

Penguindreams said...

Ah, yes. The time scale problem.

For us living today, or just us thinking on human time scales, 30 years is a pretty long time. The paleoclimatologists, once you get back to the tens of millions of years ago (like the Paleocene, or the Cretaceous-Tertiary boundary) are usually extremely happy if they can get 10-30 centuries resolution. They seldom can answer about rates of climate change in a way that is comparable to our modern interests about modern climate change.

On the other hand, sometimes they can. You just have to look hard, and find a particularly nice setting. Lakes, for instance, often leave annual layering. If you can find lake sediments that are the right age, you can get some very detailed information. Your problem is, lakes are small (hard to find) and short lived (geologically speaking, so your chances of having preserved rock are slim, even if you knew where the lake used to be).

Jesús said...

Thanks for your answer! I've been tracking back why I thought that we could get higer paleoclimatological resolutin and it seems that Grenland ice cores (GISP2) must be one of those rare exceptions, as they seem to provide higher resolution for recent events (D-O and Younger Dryas):

(1) D-O: "about 11,500 years ago, averaged annual temperatures on the Greenland icepack warmed by around 8°C over 40 years, in three steps of five years (see Alley (2000), Stewart, chapter 13) - 5°C change over 30-40 yrs more common. "
http://en.wikipedia.org/wiki/Dansgaard-Oeschger_cycles#Effect

In fact, according to the referred Allen 2000, GISP2 provide annual resolution! for some indicators.

(2) Younger Dryas: "The transitions each occurred over a period of a decade or so.[6]"
http://en.wikipedia.org/wiki/Younger_Dryas#Abrupt_climate_change

Where reference [6] points to Alley 1993:
"Oxygen isotope data from Greenland ice cores[2-4] [...]the Younger Dryas ended abruptly, over a period of about 50 years [...] dust concentrations[2][4] in these cores show an even more rapid transition (20 years)."

So I guess that this is exceptional and possible because it refers to a (geologically) recent period.

Penguindreams said...

The ice cores are why I added the comment about if you're looking farther back. For the last 15,000 years or so, the Greenland cores give us annual resolution. Back to around 100,000 years, it's a few years. Richard's comments about the transition time that you quote are milder than he's said in person (or at least, than he was saying in person when I knew him at Penn State in the early 90s), where his comment on the Younger Dryas was "However fast you believe a climate change can happen, that's how fast it was."

You might enjoy his book, if you haven't seen it yet, The Two Mile Time Machine, which is about the work on using the Greenland ice cores to figure out what has happened with climate. It's aimed at general readers, and, knowing Richard, should be both an educational read, and very enjoyable one.

quasarpulse said...

Can you point to one of the mathematically-correct "proofs" that there is no greenhouse effect? I'd be interested to see such a creature, as most such purported "proofs" I've seen have been extraordinarily painful to read.

Denis said...

Am looking for data on the earth's climate (temperature & CO2 level) going back 250 million years (such as it is). (That's about the time it takes for one revolution about our Galaxy.)

If anyone has suggestions on that (apart from "Good Luck fella"), a brief email please, at denis@ablesfamily.com & thanks

Penguindreams said...

A compilation of CO2 data is in Royer et al., at ftp://ftp.ncdc.noaa.gov/pub/data/paleo/climate_forcing/trace_gases/royer2006co2.txt

And a self-consistent model reconstruction is
ftp://ftp.ncdc.noaa.gov/pub/data/paleo/climate_forcing/trace_gases/phanerozoic_co2.txt

As you may be guessing, a place to look for paleoclimate data is the NCDC http://www.ncdc.noaa.gov/paleo/paleo.html