KESKUSTELU

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So at least in one high-latitude location, hydrates seemed to be newly giving up their methane, while reports of thawing permafrost and bubbly arctic lakes streamed in as well. But what did all the bubbling—seen and presumably unseen—really amount to? Atmospheric chemist Edward Dlugokencky of the National Oceanic and Atmospheric Administration's Earth System Research Laboratory in Boulder, Colorado, and colleagues analyzed NOAA measurements of atmospheric methane made on samples collected weekly from 1983 to 2008 at 46 sites around the world. Atmospheric methane had been increasing until the late 1990s, when it leveled off. Then in 2007, its abundance bumped up.

Taking into consideration numerous factors—including latitudinal patterns of change in atmospheric methane and shifting regional climates—Dlugokencky and his colleagues concluded that the recent methane jump was not driven by melting hydrates and permafrost. Instead, it seemed to be due to some combination of the high northern-latitude warmth in 2007 that is accelerating emissions from wetlands there; biomass burning contributing methane in the tropics; and heavy rains in Indonesia and the eastern Amazon encouraging tropical wetlands emissions. But because methane stopped increasing in the polar Northern Hemisphere in 2008, "the Arctic has not yet reached a point of sustained increased CH4 emissions from melting permafrost and CH4 hydrates," the group wrote in GRL. Dlugokencky summed up their conclusions at the AGU meeting: "Despite all the media hype, I don't think we're yet at an arctic tipping point."

Tipping points for both methane hydrates and permafrost will come, Archer predicts—but they will probably happen slowly. It takes time, he notes, to get from an atmospheric warming driven by carbon dioxide to an amplifying warming driven by atmospheric methane. It takes time for the ocean to warm. It takes time for that warmth to penetrate into hydrates. And it takes quite a bit of that penetrating heat to melt hydrates.

Once freed, the methane has to reach the atmosphere through the obvious obstacle of the overlying sediment. The ocean presents an impediment of its own. Bubbles may never reach the surface. Methane leaks out of bubbles, reacts with air dissolved in sea water, and becomes oxidized to form carbon dioxide. Even methane that reaches the atmosphere intact gets oxidized within about 10 years.

Folding all of those processes into an admittedly still-crude model, Archer and his colleagues get a warming of about 0.5°C, whether the ultimate carbon dioxide warming is a very modest 2°C or an extreme 7°C. The catch is that once the methane is converted into long-lived carbon dioxide, it prolongs that added warming for thousands of years.

So to scientists, the methane threat looks less like a catastrophe than an aggravation of a problem that already scares them. But "media people are all the time trying to have a doomsday story" about methane, says Walter Anthony. Not that scientists are blameless. "Quite a few scientists have maybe exaggerated a bit," Heimann acknowledges.

Metaanikohu - paljon melua lähes tyhjästä:

Nyt kyllä maallikko tipahti täysin!

Hiilidioksidi on lämmittänyt ilmastoa kiihtyvällä vauhdilla?

Metaania on kuitenkin jostain ilmestynyt hurjia määriä. Ilmasto sen sijaan on viilennyt viimeisinä vuosina. Viime vuosi oli kylmin globaalisti piiitkään aikaan. Samaan aikaan metaania on siis tullut ilmakehään enenevässä määrin. Ilmasto ei kuitenkaan lämmennyt?

Mistäs nyt tuulee? Niin, tiestysti, viivehän siinä on. Kummallista kun sitä viivettä ei ole ollut hiilidioksidin kanssa? Onko ilmastopolitiikassa ja koko ilmastohäslingissä enää mitään mieltä.

Tutkijat eivät tiedä, mistä metaania on yhtäkkiä tullut, mutta kuitenkin he tietävät, että ilmasto hiilidioksidin takia lämpenee 3-5 astetta 50 vuodessa. Hey c'moon. kuulostaako uskottavalta? Minusta ei?

Mikähän mättää?

[Yhdistin tähän ketjuun kolme uusinta metaaniketjua] - Phony