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Science

Peer-Review Process Confirms Contrails Climate Effect 37

Posted by timothy from the tarnished-golden-opportunity dept.
An anonymous reader writes: "According to NPR, researcher David Travis (who was mentioned in two previous articles has been published in today's issue of nature as confirming jet contrails effects on the earth's climate. The publication of this paper in arguably the most prestigious peer-reviewed scientific journal of all should help serve to assuage the spurious doubts many slashdotters voiced back in May."
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Peer-Review Process Confirms Contrails Climate Effect More

Peer-Review Process Confirms Contrails Climate Effect

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  • Should be "Nature". (Score:3, Funny)

    by Futurepower(R) ( 558542 ) on Thursday August 08, 2002 @05:27PM (#4035848) Homepage

    "today's issue of nature"

    should be: "today's issue of Nature". Nature is a science magazine.

    (This is another example that shows us that dropping out of high school is a terrible thing.)


    • > "today's issue of nature"

      > should be: "today's issue of Nature". Nature is a science magazine.

      I dunno 'bout that. After all, today is Thursday, and according to the tenants of Last Thursdayism we're due a new issue of nature today.

  • Duh? (Score:1, Insightful)

    by The Rogue86 ( 588942 )
    I'm afraid that it doesnt take a genuis to figure out that putting extra smoke in the sky is going to make more clouds and so forth......

    But alas it does take one to prove it.

    kudos to David Travis.
  • unless you live in a cold climate ( that is ) ....

    My question then becomes - do we need Contrail "spoilers" on the wings of aircraft ( probably at a reduced milage/kph rate ) and if so, what's the best design or would they even disperse enough to have contrails disappear?
    • Okay so contrails are bad... unless you live in a cold climate ( that is ) ...

      Bzzt. Naive. Global warming affects all climate zones. Some naive Canadian journalists have naively suggested that global warming would benefit Canada, because areas too cold for farming would now become arable. Or they have suggested it would be good for the summer tourist industry. Dim.

      But the effects are proving unpredictable. Will there be enough rain? Currently arable areas are experiencing drought. I have already written here about the shocking results of the Repeat of Henry Larsen's voyages [climateark.org] through the Northwest passage. The first traversal of the Northwest passage, in 1903, took Amundsen three years, because of the ice. Larsen's first trip took him 850 days, because of the ice. The vessel that repeated the voyage in 2000, easily traversed the passage, from Vancouver to Halifax in just 100 days, and encountered almost no ice...

      • Following up my wn post with some further info [wisc.edu]. This article touches on the repeat of the first west to east voyage through the Northwest Passage. But it also talks about the threat of melting permafrost.

        In the high Arctic the soil is frozen year round. Normally the top six inches or so melts long enough for plants to grow during the brief Arctic summer. But the soil below that top six inches remains frozen.

        Now it is melting, and this is a terrible development. This article says:

        When plants grow here in the Arctic, they absorb carbon from the air. But when they die they don't decay like plants in the south because they are frozen so much of the year. Eventually all that dead plant matter becomes part of the permafrost. And that makes Arctic tundra, at least until now, an important carbon sink. In fact, Arctic tundra contains one-third of the earth's stored soil carbon.

        But now the permafrost is melting, releasing eons of stored carbon. Much of this carbon will be released as Methane, which is 30 times more damaging than Carbon Dioxide.

        The scientist being interviewed estimated that recently thawed rotting vegetation from melting permafrost represented 3% of the amount of carbon flowing into the atmosphere from the combustion of fossil fuels.

        Global warming frightens me. And now I have learned of yet another reason to worry.

        • ""

          You're trying to compare a non-fossil fuel to combustion of fossil fuels. You need to find how much carbon dioxide is naturally released and compare to that.

          It is reasonable to compare the coal fires in China to combustion of fossil fuels. But you have to check whether the "combustion of fossil fuels" includes natural fires, whether coal fires are included in the other statistic, and whether they are considered natural or artificial.

          • You're trying to compare a non-fossil fuel to combustion of fossil fuels. You need to find how much carbon dioxide is naturally released and compare to that.

            Combustion is not required for Carbon to enter the atmosphere. Ordinary rotting of organic matter is also a source of both CO2 and Methane.

            The original article stated, and I quoted, the amount of CO2 that the scientist believed entered the atmosphere as a result of the decomposition of previously frozen permafrost. His estimate was that it was 3/100ths as much as entered the atmosphere from burning fossil fuels. And he suggested the rate was rapidly increasing.

            This is not like the natural release of carbon from a carbon sink, like a forest, when the forest burns. Permafrost is, well, permanent. It was laid down from at least the beginning of the last ice age. Possibly before the current cycles of ice ages. Ie. tens or hundreds of thousands of years.

            • The previous post said "represented 3%...", indicating that the 3% was part of that total.

              And now you're saying "entered the atmosphere"; do you mean "might enter the atmosphere"?

              According to the Arctic Ocean circulation theory, ice ages might happen when the Arctic warms up (the Earth is colder now than it tends to be), the ice melts, the Arctic Ocean absorbs a lot more sunlight, much more water vapor (the primary greenhouse gas) is produced..and a catastrophic amount of snow falls on the continents, beginning the growth of the glaciers.

              If we're 25-100 years from the start of a new ice age, it wouldn't be surprising if melting all that ice also thaws the permafrost. As the tundra is less reflective than ice, it should warm up more quickly...and only the last 10,000 years of accumulation will decompose because the level below that had decomposed just before the most recent ice age. I don't know how deep this might be...I'm not finding info on tundra soil depth. Many web sites say that land plants grow very slowly and footprints may remain visible for years, but there are also many shallow lakes. It would only take one inch per year of accumulation to produce a 1,000 foot depth over 12,000 years. But then why doesn't the soil in Kansas have over 1,000 feet of black soil? And where does each year's plant growth get its necessary minerals from -- from bedrock far below?

              Hmm... I wonder to what depth oxygen could penetrate. Do anaerobic bacteria also generate methane? Ah, yes they do; of course -- that's the suspected source of geologic methane deposits. So all that's needed is warmth to produce methane from organic matter.

              • The previous post said "represented 3%...", indicating that the 3% was part of that total.

                Let me encourage you again to read this article [wisc.edu]. It is quite interesting. And the questions you have all show my summary of it didn't do it justice. Your question about the depth of the permafrost is answered.

                Once you get below the active layer, which is the surface layer of the soil that thaws every year, it can be permanently frozen. And most permafrost we know in the north has been frozen for a long period of time. And it can be really thick, sometimes even over a thousand meters thick.

                The article describes the process of climbing down 30 feet into Tuktoyaktuk's community freezer.

                You ask:

                But then why doesn't the soil in Kansas have over 1,000 feet of black soil?

                "Black soil"? You mean "top soil"? Top soil is full of dead plant matter. Well, it rots. It decomposes. At least in Kansas it does.

                How deeply does oxygen penetrate permafrost? I think the answer is that it doesn't. Apparently it doesn't even penetrate marshes and bogs that well, or we wouldn't be turning up 2000 year old bog [mesh5.com] men. [mummytombs.com]

                • I saw the 1,000 meters of permafrost mentioned. I wasn't able to find the depth which would have accumulated since the last ice age. If an ice age is usually preceded by an arctic thaw, the tundra material before the last ice age would have already decomposed and won't contribute more methane.

                  Yes, I was referring to former topsoil. Rather than Kansas having hundreds of feet of accumulated topsoil, the Kansas Geological Survey [ukans.edu] doesn't even map it. Perhaps erosion is so powerful that it washes away topsoil faster than it can be formed -- but if that were the case it should be gone. If permafrost material accumulates faster than topsoil accumulates in faster-growing warm climates, either topsoil is removed faster in warmer climates or the removal is blocked by the arctic climate. (I used the term "permafrost material" because I suspect that the many shallow lakes contribute an amount similar to that of trundra plants).

                  And I agree that oxygen wouldn't penetrate thawed permafrost very deeply, which is why I was wondering if anaerobic bacteria generate methane. They do, so we don't have to wait for oxygen to penetrate thawed permafrost, as decomposition will start as soon as it warms up (I'm sure there already are bacteria frozen in there so there is no travel time).

                  So we might be watching a thawing that triggers the next ice age; one is expected soon so it is not surprising. The methane from the permafrost might increase temperatures briefly, but it only lasts 50 years in the atmosphere and then its "greater warming than carbon dioxide" behavior will be gone. (By what percent would permafrost methane increase the amount of methane in the atmosphere?)

  • If I understood the article correctly, jet contrails, locally counteract global warming, shifting the temperature down 1.8 degrees centigrade.

    I guess I should tell those airport expansion opponents they're ruining the local microclimate...
    • If I understood the article correctly, jet contrails, locally counteract global warming, shifting the temperature down 1.8 degrees centigrade.

      Nope. You read it wrong. They compared the difference in temperature between night and day. The existence of jet contrails are correlated to a smaller difference in temperature -- presumably, the days were cooler, and the nights were warmer than normal.

      The idea is that sunlight bounces off the top of the contrails during the day, and reflects back into space. Thus, less energy is added to the environment during the day, which means that the jets have the immediate effect of cooling the earth, but only during the day.

      However, the heat radiated up from the ground also gets reflected right back to the ground, just as if you'd put a big blanket over the earth. This has the effect of generally warming the earth, during both day and night.

      So, there are all sorts of questions which are, hopefully, outside the scope of an article like this. I'm not sure, because I've only read the brief linked writeup, not the real [nature.com] paper published in Nature. Reading the paper costs money to read, and I'm cheap.

      The questions I immediately have is: do the contrails have the net effect of increasing or decreasing the total amount of energy stored in the earths environment, i.e., do they actaually cool or warm the earth? Which has a bigger effect -- the light reflecting off the top and into space, or the heat reflected back onto the surface? What are the magnitudes of each of these effects across different seasons? What are the effects across different regions of the world? What effect does this actually have on the climate -- rainfall patterns, regional mean termperatures, or regional temperature variance.
      • Since contrails dissipate after a short while and planes fly more during the daytime than during nightime wouldn't the reflective effect tend to be stronger than the retentive effect?

  • Repeatability? (Score:2, Interesting)

    by U96 ( 538500 )
    I could agree that contrails are bad and I'm willing to acknowledge that global warming is a problem, but I'm worried that there's some bad science happening here. Maybe I've missed something, but just because the temperatures where different on those 3 days from averages during the same month over the past 23 years, how can you assume this was caused by the absence of the contrails? Wouldn't you need to be able to repeat the experiment several times before you could rule out a fluke? "Travis's team compared the average daily high and low temperatures over North America from 11 to 14 September 2001, with climatic records from 1977 to 2000, matching the weather over those three days with similar weather in September from historical records."
    • You get all commercial airflight to cease next month, and I'll be sure to write down the temperatures.

      Tim
    • Wouldn't you need to be able to repeat the experiment several times before you could rule out a fluke?

      Hmmm. Can I remind you that this "experiment" covered every part of the USA? Since the USA is a big country, finding the same effect all over is better than just testing a single location.

      I'd be willing to ground the entire US commercial air-fleet for another experiment, to build more confidence though.

      • I wasn't suggesting we ground all aircraft again. I was just wondering whether the results are reliable given that it was a one-time event. I suppose someone has chosen their statistics carefully.
    • I could agree that contrails are bad

      Who are you agreeing with? No-one claimed they're bad. They only claimed there was an effect.

      how can you assume this was caused by the absence of the contrails?

      I haven't paid the money to read the real article (instead of the brief writeup), but I have to assume that they don't say that contrails caused this. That's the sort of thing clueless AP reporters and Slashdot "editors" do, not scientists. The article probably says something, "Here is a measurement. Here is the statistical significance of the correlation between changes in this measurement and 9/11. Here is a possible explanation for this correlation. The end."

      Wouldn't you need to be able to repeat the experiment several times before you could rule out a fluke?

      No, of course not. You should take an introductory statistics class, where this kind of stuff is explained more clearly. You can never rule it out as a fluke, no matter how many experiments you do. The best you can ever do is state the probability that it was a fluke. You can even state the probability when you get a sample size of one. I'm assuming that they've done exactly that in the real article, but again, I haven't paid to read it.

      Now, of course the fact that the expirament is not easily repeatable does create a conundrum. Even if they did get a result with, say, p < 0.05, it's impossible for us to know how many researchers tried how many dozens (or even hundreds) of different measurements before finding a statistically significant one. If the scientific communinity, as a body, went fishing for data after the event, it's pretty much assured that they're going to find something statistically significant to report on, along with a bunch of stuff which is not statistically signficant. By the very nature of a peer-review journal like Nature, it's a given that the non-statistically significant stuff simply won't get published, and thus not show up on Slashdot's doorstep...

  • Peer review doesn't mean the research is right... (Score:3, Insightful)

    by Peter T Ermit ( 577444 ) on Thursday August 08, 2002 @05:55PM (#4035992)
    It just means that it passes the giggle test. Sometimes it doesn't even mean that. (Nature had its transgenic corn thing and Science had its bubble fusion recently.) It's a big mistake to confuse the imprimatur of a science journal with acceptance by the scientific community.
  • that TNG
    episode [startrek.com]
    where flying around at warp speeds was going to destroy the universe.
  • And I'm supposed to believe that this "obviously proves" something? They would be a lot more believable if they included other possible causes that they were able to DISPROVE. Smells like somebody is grasping at straws to get their grant renewed.
  • Obviously, the contrails can initiate cloud formation and cause a local affect, but whatever premature energy transfer occurs (condensation, precipitation, absorption, reflection) would have occured eventually. Looking at the big picture, the amount of energy introduced into the atmosphere by an aircraft is insignificant, even though it can initiate a significant weather event. It's a "robbing Peter to pay Paul" kind of thing.

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