"Derretimento de "metano em gelo" provocou aquecimento.."

Tópico em 'Media' iniciado por ecobcg 30 Mai 2008 às 17:13.

  1. ecobcg

    ecobcg
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    Melting of methane ice triggered long-ago warming surge: study


    by Staff Writers
    "Paris (AFP) May 28, 2008
    Melting of methane ice unleashed runaway global warming some 635 million years ago, according to a study released Wednesday that has implications for today's climate-change crisis.
    Release of the potent greenhouse-gas, at first in small amounts and then in massive volumes, brought a sudden end to the planet's longest Ice Age, its authors believe.

    During the "Snowball Earth" era, Earth froze over completely, with glaciers that crept down into the tropics and possibly even reached the equator.

    The chill was self-sustaining, because the ice formed a brilliant white shell that reflected the Sun's rays, preventing the surface from warming.

    After a frozen slumber lasting 155 million years, Earth warmed dramatically.

    How this happened has been fiercely disputed, although all agree that the event changed the planet's climate system and ocean chemistry forever.

    Publishing in the weekly British journal Nature, scientists in the United States and Australia point the finger at methane clathrates -- methane-rich ice that forms under ice sheets at specific temperatures and pressures.

    The researchers believe that the ice sheets on Snowball Earth became unstable, which released pressure on the clathrates.

    They began to evaporate, releasing the methane, which helped to warm the planet slightly. This thawed more clathrates and fuelled the warming and so on, creating a vicious circle or "positive feedback" in scientific parlance.

    Methane is a prodigious greenhouse gas, being 30 times more efficient than CO2 in trapping solar heat.

    Martin Kennedy, a geologist at the University of California Riverside who led the study, said the evidence comes from hundreds of marine sediment samples taken in South Australia.

    Analysis of them for oxygen isotopes gave a signature of melting waters in ice sheets and destabilisation of clathrates by the meltwater.

    Kennedy says the findings have a bearing on a much-feared positive feedback today -- the release of methane from frozen soil in Canada, Siberia and Alaska, and from clathrates that are below sea level, at the continental margins of the ocean.

    Billions of tonnes of methane are locked up in these reservoirs, and the big worry is that it could take a relative small rise in temperature to start unleashing the gas, which would then trigger an unstoppable warming cycle.

    "One way to look at the present human influence on global warming is that we are conducting a global-scale experiment with Earth's climate system," said Kennedy.

    "We are witnessing an unprecedented rate of warming, with little or no knowledge of what instabilities lurk in the climate system and how they can influence life on Earth."

    If the end of Snowball Earth is a guide, positive feedbacks, "once initiated, change the climate to a wholly different state," he observed.

    If the mechanism for clathrates' feedback is now clearer, the scientists have still to explain how much forcing was needed for the vicious circle to set in motion -- and whether we are approaching any similar threshold today with the CO2 from fossil fuels.

    Meanwhile, other research, also published in Nature, explains a mysterious fall in temperature which was noted in 1945 and has irked climate investigation for decades.

    The fall was not due to a sudden cooling as some have suggested, but to different ways in which sea temperatures were measured by ocean-going ships, it says.
    "

    in www.terradaily.com
     
  2. José M. Sousa

    José M. Sousa
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    Já não bastava este problema, agora os japoneses e outros, querem explorar comercialmente os clatratos:

    http://www.odac-info.org/node/1780

    «[...] make it abundantly clear that widespread extraction and use of even a seemingly small fraction of the world’s methane hydrates would be extremely undesirable from a global climate perspective, if such use results in further unconstrained emissions of CO2 (or methane).»
     
  3. psm

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    Já tinha posto alguns posts em relação a este assunto.Este assunto dos hidratos de metano é que é perigoso.
     
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  4. José M. Sousa

    José M. Sousa
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    http://climateprogress.org/2008/09/23/has-runaway-climate-change-begun

    Has runaway climate change begun?
    The UK’s Independent reported today some pretty shocking news in “Exclusive: The methane time bomb“:
    The first evidence that millions of tons of a greenhouse gas 20 times more potent than carbon dioxide is being released into the atmosphere from beneath the Arctic seabed has been discovered by scientists.
    The Independent has been passed details of preliminary findings suggesting that massive deposits of sub-sea methane are bubbling to the surface as the Arctic region becomes warmer and its ice retreats.
    Assuming these findings are published in a peer-reviewed publication, as is planned, they should be taken quite seriously for four reasons. First, many fear that a huge methane release is what happened during the Permian-Triassic extinction event and the Paleocene-Eocene Thermal Maximum. Second, releasing even a small fraction of the sub-sea methane would make a stabilizing greenhouse gas emissions at non-catastrophic concentrations all but impossible.
    Third, as NOAA reported earlier this year, levels of methane rose sharply last year for the first time since 1998:

    Fourth, the findings are apparently based on very new and credible in situ measurements:
    Scientists aboard a research ship that has sailed the entire length of Russia’s northern coast have discovered intense concentrations of methane — sometimes at up to 100 times background levels — over several areas covering thousands of square miles of the Siberian continental shelf.
    In the past few days, the researchers have seen areas of sea foaming with gas bubbling up through “methane chimneys” rising from the sea floor. They believe that the sub-sea layer of permafrost, which has acted like a “lid” to prevent the gas from escaping, has melted away to allow methane to rise from underground deposits formed before the last ice age.
    They have warned that this is likely to be linked with the rapid warming that the region has experienced in recent years….
    Since 1994, Igor Semiletov of the Far-Eastern branch of the Russian Academy of Sciences “has led about 10 expeditions in the Laptev Sea but during the 1990s he did not detect any elevated levels of methane. However, since 2003 he reported a rising number of methane “hotspots,” which have now been confirmed using more sensitive instruments.” Why now?
    Dr Semiletov has suggested several possible reasons why methane is now being released from the Arctic, including the rising volume of relatively warmer water being discharged from Siberia’s rivers due to the melting of the permafrost on the land.
    The Arctic region as a whole has seen a 4C rise in average temperatures over recent decades and a dramatic decline in the area of the Arctic Ocean covered by summer sea ice. Many scientists fear that the loss of sea ice could accelerate the warming trend because open ocean soaks up more heat from the sun than the reflective surface of an ice-covered sea.
    The article notes that the “preliminary findings of the International Siberian Shelf Study 2008″ are “being prepared for publication by the American Geophysical Union.” Until that happens, it will be difficult to know what to make of all this. You can read what some other scientists say about these preliminary reports here. Stay tuned.
    The time to act is yesterday.

    artigo do jornal Independent

    Exclusive: The methane time bomb
    Arctic scientists discover new global warming threat as melting permafrost releases millions of tons of a gas 20 times more damaging than carbon dioxide
    By Steve Connor, Science Editor
    Tuesday, 23 September 2008
    The first evidence that millions of tons of a greenhouse gas 20 times more potent than carbon dioxide is being released into the atmosphere from beneath the Arctic seabed has been discovered by scientists.
    The Independent has been passed details of preliminary findings suggesting that massive deposits of sub-sea methane are bubbling to the surface as the Arctic region becomes warmer and its ice retreats.


    Underground stores of methane are important because scientists believe their sudden release has in the past been responsible for rapid increases in global temperatures, dramatic changes to the climate, and even the mass extinction of species. Scientists aboard a research ship that has sailed the entire length of Russia's northern coast have discovered intense concentrations of methane – sometimes at up to 100 times background levels – over several areas covering thousands of square miles of the Siberian continental shelf.
    In the past few days, the researchers have seen areas of sea foaming with gas bubbling up through "methane chimneys" rising from the sea floor. They believe that the sub-sea layer of permafrost, which has acted like a "lid" to prevent the gas from escaping, has melted away to allow methane to rise from underground deposits formed before the last ice age.
    They have warned that this is likely to be linked with the rapid warming that the region has experienced in recent years.


    Methane is about 20 times more powerful as a greenhouse gas than carbon dioxide and many scientists fear that its release could accelerate global warming in a giant positive feedback where more atmospheric methane causes higher temperatures, leading to further permafrost melting and the release of yet more methane.
    The amount of methane stored beneath the Arctic is calculated to be greater than the total amount of carbon locked up in global coal reserves so there is intense interest in the stability of these deposits as the region warms at a faster rate than other places on earth.
    Orjan Gustafsson of Stockholm University in Sweden, one of the leaders of the expedition, described the scale of the methane emissions in an email exchange sent from the Russian research ship Jacob Smirnitskyi.
    "We had a hectic finishing of the sampling programme yesterday and this past night," said Dr Gustafsson. "An extensive area of intense methane release was found. At earlier sites we had found elevated levels of dissolved methane. Yesterday, for the first time, we documented a field where the release was so intense that the methane did not have time to dissolve into the seawater but was rising as methane bubbles to the sea surface. These 'methane chimneys' were documented on echo sounder and with seismic [instruments]."
    At some locations, methane concentrations reached 100 times background levels. These anomalies have been seen in the East Siberian Sea and the Laptev Sea, covering several tens of thousands of square kilometres, amounting to millions of tons of methane, said Dr Gustafsson. "This may be of the same magnitude as presently estimated from the global ocean," he said. "Nobody knows how many more such areas exist on the extensive East Siberian continental shelves.
    "The conventional thought has been that the permafrost 'lid' on the sub-sea sediments on the Siberian shelf should cap and hold the massive reservoirs of shallow methane deposits in place. The growing evidence for release of methane in this inaccessible region may suggest that the permafrost lid is starting to get perforated and thus leak methane... The permafrost now has small holes. We have found elevated levels of methane above the water surface and even more in the water just below. It is obvious that the source is the seabed."


    The preliminary findings of the International Siberian Shelf Study 2008, being prepared for publication by the American Geophysical Union, are being overseen by Igor Semiletov of the Far-Eastern branch of the Russian Academy of Sciences. Since 1994, he has led about 10 expeditions in the Laptev Sea but during the 1990s he did not detect any elevated levels of methane. However, since 2003 he reported a rising number of methane "hotspots", which have now been confirmed using more sensitive instruments on board the Jacob Smirnitskyi.
    Dr Semiletov has suggested several possible reasons why methane is now being released from the Arctic, including the rising volume of relatively warmer water being discharged from Siberia's rivers due to the melting of the permafrost on the land.
    The Arctic region as a whole has seen a 4C rise in average temperatures over recent decades and a dramatic decline in the area of the Arctic Ocean covered by summer sea ice. Many scientists fear that the loss of sea ice could accelerate the warming trend because open ocean soaks up more heat from the sun than the reflective surface of an ice-covered sea.
     

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