Nuclear Winter - science or myth?

[Gokul43201]

What, if any, will be the effects of a large scale nuclear war (~a few Mt distributed over major cities in at least 2 industrialized countries), on global climate in the months and years following the event? How well does the current state of science in this field permit an answer to the above question, and what conclusions can be made to different levels of uncertainty?

 

[Andre]

I don't know, but what we do know is the effect of large aerosol producing volcanoes on the weather. For instance the 'recent' Agung, El Chichon and Pinatubo volcanoes in http://www.metoffice.gov.uk/research/hadleycentre/pubs/brochures/2005/clim_green/slide31.pdf, causing the year without summer in 1816, is that equivalent to a nuclear winter?

 

[vanesch]

I thought that the extinction at the K-T boundary was due to such a "nuclear" (impact) winter scenario, or is this put in doubt ?

 

[mheslep]

From Freeman Dyson's book http://books.google.com/books?id=Ca...BA&sig=VVVOiyUD15imEdTaZLw_KnSXVKQ#PPA260,M1":

... I judge the nuclear winter theory to be sloppy piece of work, full of gaps and and unjustified assumptions. As a human being, I hope fervently that it is right... since I am a scientist dedicated to truth, I will criticize nuclear winter theory as harsly as I would criticize any other half-baked scientific theory.

and more relevant to the AGW politics of today:

...Few of my colleagues have had the courage to make this ... response

 

[Gokul43201]

From Freeman Dyson's book http://books.google.com/books?id=Ca...BA&sig=VVVOiyUD15imEdTaZLw_KnSXVKQ#PPA260,M1":

Do you have a reference that is not a quarter of a century old? I don't doubt that early versions were filled with holes, but I'm curious if all the recent work is also debunked or discredited.

Robock, Alan, Luke Oman, Georgiy L. Stenchikov, Owen B. Toon, Charles Bardeen, and Richard P. Turco, "Climatic consequences of regional nuclear conflicts" Atm. Chem. Phys., 7, 2003-2012 (2007)

Robock, Alan, Luke Oman, and Georgiy L. Stenchikov, "Nuclear winter revisited with a modern climate model and current nuclear arsenals: Still catastrophic consequences" J. Geophys. Res., 112 13107 (2007)

Toon, Turco, Robock, Bardeen, Oman, and Stenchikov, "Atmospheric effects and societal consequences of regional scale nuclear conflicts and acts of individual nuclear terrorism" Atm. Chem. Phys., 7 1973-2002 (2007)

Toon, Robock, Turco, Bardeen, Oman, and Stenchikov, "Consequences of regional-scale nuclear conflicts" Science, 315 1224-1225 (2007)

Most/all of the above papers can be accessed from here: http://climate.envsci.rutgers.edu/nuclear/

 

[Gokul43201]

I don't know, but what we do know is the effect of large aerosol producing volcanoes on the weather. For instance the 'recent' Agung, El Chichon and Pinatubo volcanoes in http://www.metoffice.gov.uk/research/hadleycentre/pubs/brochures/2005/clim_green/slide31.pdf, causing the year without summer in 1816, is that equivalent to a nuclear winter?

I don't know how good or bad such a comparison would be, but I can't think of very much better empirical data to use (nuclear tests, for instance, are not great to use because they are much smaller, and designed specifically to avoid civilization and hence minimize the size of dust plumes that might affect climate). The differences, however, are notable, and might be enough to make any extrapolation useless. For instance, with volcanic activity far removed from urban settlements, almost all long term climatic effects are supposedly due to sulfates that get dispersed in the atmosphere. This is not the case with a nuclear event.

I thought that the extinction at the K-T boundary was due to such a "nuclear" (impact) winter scenario, or is this put in doubt ?

I think this may be the best theory currently, but perhaps it's not the only one. I don't know if alternate theories even come close, but I know very little about this field. But, for whatever it's worth, I too am not aware of anything new that has put it in doubt, but I was also not aware that it was essentially the cooling period following impact that was proposed as the cause of extinction.

 

[mheslep]

Do you have a reference that is not a quarter of a century old? I don't doubt that early versions were filled with holes, but I'm curious if all the recent work is also debunked or discredited.

Thanks for the links.

When I read 'nuclear winter' I think of the term as made infamous by the paper by Sagan, Turco, Toon, Ackerman, and Pollack; and then the Cold and the Dark book by Erlich, Sagan, Donald Kennedy (now Science editor) and Roberts. In that 1983 work they claimed an average global temperature drop of http://books.google.com/books?id=ht...BA&sig=SFuiZf0h9OKOYWCmPqctwyqtsi0#PPA570,M1" without much qualification. Sagan then went on ABC's Nightline in '91 and predicted that the Kuwaiti oil fires would cause similar effects.(To his credit Sagan later acknowledged his error). On this topic it is only these nuclear winter publications and public announcements that I cite as examples of bad science, because only they have claims outlandish enough to warrant the term 'winter' IMO.

As far as I can see the newer work is talking about 4 to 10C drops and cooling 'signals' from Pinatubo and the like; I have no idea of their validity, though I'm skeptical of the large reliance on the NASA model - creating again the falsification problem.

 

[Andre]

Our knowlegde level about the cause of the K-T extinction is increasing more a definite maybe. Speculations include global climate changes due to *natural* causes, as the number of dino species decreased below the famous iridium layer, associated with the Chicxulub crater, under the sediments of the Yucatán. But there is also the mega basalt flood Volcano in India, the Deccan Traps.

There used to be an hypothesis that a mega imact can trigger antipodal flood basalt mechanism, and indeed at that point in time 65 Ma, India was possibly antipode to the Caribean. However a problematic challenge for that hypothesis is dating, it seems that the Deccan traps predate the Chicxulub with a few 100,000 years. Hence it might be that the volcano was more important for the extinction than the impact. Note that the Deccan Traps were a few orders of magnitude heavier than anything we know in recent times

This compares with the superlatives of both, the greatest extinction of all times, the Permo-triassic event codates closely with the largest known volcanic events, the Siberian traps, erupting 3 million cu km, versus http://users.bendnet.com/bjensen/volcano/largerup.html of the Tambora.

Of course, no matter how many dust particles are in the air, it does not change the time required for it to settle again. So even after the Siberian Traps the air would be clear again after few years.

 

[D H]

From my readings, current thinking is that the Deccan traps and the Chicxulub impactor dealt Earth a one-two punch. Moreover, the Shoemaker-Levy impact with Jupiter has lead some to speculate that multiple impactors hit the Earth around the same time. Multiple craters appear to have more or less the same age. Chicxulub was possibly one of many. Tycho on the Moon is posited as another impactor from the same family; see http://www.boulder.swri.edu/~bottke/Reprints/Bottke_2007_Nature_449_48_Baptistina_KT.pdf

How big was it? The crater is 180 km in diameter. It takes a huge explosion make this large a crater. Our largest nuclear weapons pale in comparison. Wikipedia cites 500 zettajoules, or two million times as powerful as the Emperor Bomb. Using the K-T extinction as a justification for the nuclear winter hypothesis is not valid because of the huge difference in scale between Chicxulub and our weaponry, even if we lit off all of our weapons at once.

 

[Ivan Seeking]

..."Our research supports that there would be worldwide destruction," said Michael Mills, co-author of the study and a research scientist at the University of Colorado at Boulder. "It demonstrates that a small-scale regional conflict is capable of triggering larger ozone losses globally than the ones that were previously predicted for a full-scale nuclear war."

Combined with the climatic impact of a regional nuclear war -- which could reduce crop yields and starve hundreds of millions -- Mills' modeling shows that the entire globe would feel the repercussions of a hundred nuclear detonations, a small fraction of just the U.S. stockpile. After decades of Cold War research into the impacts that a full-blown war between the Soviet Union and the United States would have had on the globe, recent work has focused on regional nuclear wars, which are seen as more likely than all-out nuclear Armageddon. Incorporating the latest atmospheric modeling, the scientists are finding that even a small nuclear conflict would wreak havoc on the global environment (.pdf) -- cooling it twice as much as it's heated over the last century -- and on the structure of the atmosphere itself.

Mills' work, which appears online today in the Proceedings of the National Academies of Science, used a model from National Center for Atmospheric Research to look at the impact of throwing 5 million metric tons of black carbon, or soot, into the atmosphere. [continued]

http://blog.wired.com/wiredscience/2008/04/regional-nuclea.html

 

[fluidistic]

Humans already have exploded hundreds of atomic bombs and some H-bombs, of course not over cities (well, except in Japan). From this stupidity Earth is contaminated, especially the calcium... But I don't think it affected the climate till now. Now it is forbidden to test nuclear bombs... after having damaged Earth. (The wave under the floor of an h-bomb could be detected on seismograph and it is said to make approximately 3 times the circumference of the Earth). Yet nothing about nuclear winter.

 

[Ivan Seeking]

Proximity to the ground determines the amount of material thrown into the atmosphere, so one would have to consider the altitude at which the blast occurred as well as the size of the blast in order to compare the results to the study mentioned above. Note also that many tests were done over water which would not eject large quantities of soot into the atmosphere.

 

[vanesch]

Humans already have exploded hundreds of atomic bombs and some H-bombs, of course not over cities (well, except in Japan). From this stupidity Earth is contaminated, especially the calcium...

It's a good thing that atmospheric tests stopped, but one must not exaggerate: at the peak in 1963, the average dose received by atmospheric tests was 0.15 mSv/year which has, by now, dropped to 0.005 mSv/year.

As a comparison, the natural background dose you receive each year from natural processes is on average 2.4 mSv/year (but depends on the place where you live).

http://en.wikipedia.org/wiki/Background_radiation

 

[fluidistic]

I didn't want to exaggerate. That's what I've read some years ago. I can't find any sources for now. But maybe an important observation, from wikipedia "La Communauté européenne a fixé des doses de radioactivité à ne pas dépasser dans les aliments : le lait ne doit pas dépasser 500 Bq/l pour l'iode 131. Dans certains länder allemands, les normes sont beaucoup plus sévères (100 Bq/l en Sarre, 20 Bq/l en Hesse et Hambourg)."
Which says that the European Community has established a maximum dose of radioactivity for milk. (Which is well known to contain calcium). I'm pretty sure this resolution is quite new compared to the beginning of the atomic bomb era.
So trust what you want, but it seems that calcium was more affected by radioactivity than "the global environment".

 

[vanesch]

Which says that the European Community has established a maximum dose of radioactivity for milk. (Which is well known to contain calcium). I'm pretty sure this resolution is quite new compared to the beginning of the atomic bomb era.
So trust what you want, but it seems that calcium was more affected by radioactivity than "the global environment".

No, this has to do with two other issues, which have nothing to do with nuclear bomb tests: Chernobyl on one hand, and German politiking against nuclear power on the other.

What counts, in the end, is what is the dose of effective ionising radiation that a member of the public receives (in the "reference group"), and how this compares to natural doses and their fluctuations that these people undergo in any case.

To give you an idea, each chemical element has to it what's called a "radiotoxicity", which gives you the ratio of the *engaged dose* from that chemical element per unit of activity of that element.

The engaged dose is the total dose, over 50 years, that you will receive from the ingestion or inhalation (the two are different), the mobility of the element in your body, the biological elimination and the radioactive decay, and the relative sensitivity of different organs to radiation. One has established biological models for most of the elements, done the calculation of the effective doses one gets from it, and that gives you the "radiotoxicity". For ingestion, for nasty elements from 10^-7 Sv/Bq to more benign elements of 10^-10 Sv/Bq, and most are around 10^-8 or 10^-9 Sv/Bq. These things are worse for inhalation, as the lungs are more sensitive, and the elimination is less.

 

[fluidistic]

Okay, thank you, at least I learned something about it. So what I've read some years ago was just exaggeration I guess.