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Affichage des articles dont le libellé est Mer. Afficher tous les articles
Affichage des articles dont le libellé est Mer. Afficher tous les articles
mercredi 4 septembre 2013
lundi 26 août 2013
Science points to a new global warming source: the sea
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| Lightning strikes on the Pacific Ocean on Panama Bay on June 24, 2013. Oceans that grow more acidic through Man's fossil fuel burning emissions, can amplify global warming by releasing less of a gas that helps shield Earth from radiation, a study said Sunday. |
Oceans that grow more acidic through Man's fossil fuel burning emissions, can amplify global warming by releasing less of a gas that helps shield Earth from radiation, a study in Nature Climate Change said Sunday.
And the authors warned the potentially vast effect they uncovered is not currently factored into climate change projections.
Scientists say that Man's carbon dioxide (CO2) emissions contribute to planetary warming by letting the Sun's heat through the atmosphere but trapping heat energy reflected back from Earth, so creating a greenhouse effect.
They also lower the pH balance of the world's oceans, making them more acidic, and hamper production of dimethyl sulphide (DMS), a sulphur compound, by plankton, said the study.
DMS released into the atmosphere helps reflect incoming radiation from the Sun, reducing surface temperatures on Earth.
Using climate simulations, the team said an 18 percent decline in DMS emissions by 2100 could contribute as much as 0.48 degrees Celsius (0.9 deg Fahrenheit) to the global temperature.
"To our knowledge, we are the first to highlight the potential climate impact due to changes in the global sulphur cycle triggered by ocean acidification," the authors wrote.
"Our result emphasises that this potential climate impact mechanism of ocean acidification should be considered in projections of future climate change."
They warned that ocean acidification may also have other, yet unseen, impacts on marine biology that may provoke further declines in DMS emissions.
Explore further: Dire outlook despite global warming 'pause': study
More information: dx.doi.org/10.1038/nclimate1981
Journal reference: Nature Climate Change
© 2013 AFP
16 hours ago
Read more at: http://phys.org/news/2013-08-science-global-source-sea.html#jCp
And the authors warned the potentially vast effect they uncovered is not currently factored into climate change projections.
Scientists say that Man's carbon dioxide (CO2) emissions contribute to planetary warming by letting the Sun's heat through the atmosphere but trapping heat energy reflected back from Earth, so creating a greenhouse effect.
They also lower the pH balance of the world's oceans, making them more acidic, and hamper production of dimethyl sulphide (DMS), a sulphur compound, by plankton, said the study.
DMS released into the atmosphere helps reflect incoming radiation from the Sun, reducing surface temperatures on Earth.
Using climate simulations, the team said an 18 percent decline in DMS emissions by 2100 could contribute as much as 0.48 degrees Celsius (0.9 deg Fahrenheit) to the global temperature.
"To our knowledge, we are the first to highlight the potential climate impact due to changes in the global sulphur cycle triggered by ocean acidification," the authors wrote.
"Our result emphasises that this potential climate impact mechanism of ocean acidification should be considered in projections of future climate change."
They warned that ocean acidification may also have other, yet unseen, impacts on marine biology that may provoke further declines in DMS emissions.
Explore further: Dire outlook despite global warming 'pause': studyMore information: dx.doi.org/10.1038/nclimate1981
Journal reference: Nature Climate Change
© 2013 AFP
16 hours ago
Read more at: http://phys.org/news/2013-08-science-global-source-sea.html#jCp
lundi 19 août 2013
dimanche 18 août 2013
Une puce électronique pour dessaler l’eau de mer
Une nouvelle technique de dessalement basée sur une réaction chimique se révèle peu couteuse.
Des chercheurs de l’université du Texas à Austin et de celle de Marburg en Allemagne ont collaboré avec la société Okeanos Technologies pour fabriquer une puce électronique permettant de dessaler l’eau de mer. Le principe est simple : l’eau de mer s’écoule entre plusieurs micro-canaux de 22 microns de diamètre. Chacun d’entre eux se divise en deux.
Au point de séparation, une électrode impose une tension qui oxyde les ions chlorure. La disparition de ces ions provoque un gradient de champ magnétique qui pousse les ions chargés positivement vers la sortie. Les ions chargés négativement sont alors attirés par ceux chargés positivement. Un canal contient donc les ions chargés, tandis que dans le deuxième coule une eau partiellement dessalée.
Les avantages de cette approche sont sa simplicité de mise en œuvre, son besoin en énergie limité puisque des piles du commerce suffiraient à l’alimenter, et donc son faible coût. Reste cependant à améliorer le rendement. A ce jour, le taux de désalinisation est de seulement 25% maximum. Un taux qui doit impérativement atteindre les 99% pour que l’eau soit considérée comme potable.
Paru dans le journal Angewandte Chemie, ces travaux proposent une alternative prometteuse aux techniques actuelles dont la distillation ou l’osmose inverse, très efficaces mais très chères à mettre en œuvre.
Par Audrey Loubens, journaliste scientifique
16 août 2013
Des chercheurs de l’université du Texas à Austin et de celle de Marburg en Allemagne ont collaboré avec la société Okeanos Technologies pour fabriquer une puce électronique permettant de dessaler l’eau de mer. Le principe est simple : l’eau de mer s’écoule entre plusieurs micro-canaux de 22 microns de diamètre. Chacun d’entre eux se divise en deux.
Au point de séparation, une électrode impose une tension qui oxyde les ions chlorure. La disparition de ces ions provoque un gradient de champ magnétique qui pousse les ions chargés positivement vers la sortie. Les ions chargés négativement sont alors attirés par ceux chargés positivement. Un canal contient donc les ions chargés, tandis que dans le deuxième coule une eau partiellement dessalée.
Les avantages de cette approche sont sa simplicité de mise en œuvre, son besoin en énergie limité puisque des piles du commerce suffiraient à l’alimenter, et donc son faible coût. Reste cependant à améliorer le rendement. A ce jour, le taux de désalinisation est de seulement 25% maximum. Un taux qui doit impérativement atteindre les 99% pour que l’eau soit considérée comme potable.
Paru dans le journal Angewandte Chemie, ces travaux proposent une alternative prometteuse aux techniques actuelles dont la distillation ou l’osmose inverse, très efficaces mais très chères à mettre en œuvre.
Par Audrey Loubens, journaliste scientifique
16 août 2013
dimanche 21 juillet 2013
The Great Sahara Sea That Almost Was
In 1874, Captain Francois-Elie Roudaire, a geographer in the French army proposed a daring idea. No doubt inspired by the successful completion of the Suez canal a few years earlier, he suggested the creation of a 120-mile-long canal that would connect the Mediterranean Sea to a part of the Sahara Desert in Algeria that lies below sea level. The result would be the flooding of more than 3000 square miles of territory. Roudaire hoped that such a huge body of water would not only allow ships to navigate into the interior of North Africa, it would also significantly change the local climate. All at a cost of a mere 25 million francs.
Waterfront property in Timbuctoo.
The engineer behind the construction of the Suez Canal, Ferdinand de Lesseps, gave Roudaire's scheme his blessing, which was all the French public needed to hear, what with de Lesseps being a national hero and all. The French Academy of Sciences pitched in with a special commission and the French government pledged 35,000 francs to get the ball rolling. Most of this was earmarked to send an expedition, led by Roudaire, to North Africa to study the feasibility of the plan.
The London Times said that the plan "dazzles the imagination, yet it has a sufficiently substantial basis to satisfy several shrewd traders in African commerce and some distinguished engineers." The Daily News called the project "the most remarkable that has ever been devised."
This new sea "is sure to be frequented by trading vessels," reported the British magazine All the Year Round, "to carry off the produce of its banks, which will eventually be dotted with groves of date and coconut palms...Hotels, perhaps towns, will spring up on picturesque and eligible sites; luxurious house-boats will float in its most sheltered and shady creeks..."
Roudaire worked tirelessly for the next eight years, but as scientists and engineers gradually turned against the scheme — the former citing bad geography and geology and the latter an expense that had ballooned to over a billion francs — the idea slowly grew out of favor. Not the least problem was the discovery that the chott (a dry salt lake) nearest the Mediterranean was actually above sea level. Roudaire tried to save his scheme by lengthening his canal from about ten miles long to more than a hundred miles while also decreasing the area that would be flooded.
But in spite of all his efforts, the plan was eventually abandoned. Roudaire died not long afterward, at the age of 48 in 1885, of a fever picked up during his final expedition.
Although the Sahara Sea fell out of favor with engineers, politicians and the public, the sheer grandness and audacity of the idea appealed to a best-selling science fiction author. Jules Verne had already alluded to the scheme in his 1877 novel "Off on a Comet!" (a.k.a. "Hector Servadac"), in which he refers the sea as a going concern. But even 30 years later, the idea still attracted him. He describes the construction of the canal in his 1905 novel, "The Invasion of the Sea," as well as the catastrophic creation of the inland sea when an ill-timed earthquake unexpectedly moves the engineer's schedule up.
The idea has never been entirely abandoned, however, and is periodically unearthed. Even the CIA has explored the consequences of flooding the Qattara Depression in Libya. One advantage that intrigues modern engineers is the possibility of generating massive quantities of hydroelectric power. It would require a canal (or a pair of tunnels ,according to one proposal) only 40 miles long to connect the depression with the sea. The drop of 440 feet would be more than sufficient for the generation of power. Concerns over things such as the impact on indigenous peoples and wildlife are among the many major obstacles to these plans.
[Via Archive.org and The Basement Geographer]
http://io9.com/the-great-sahara-sea-that-almost-was-837206551?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+io9%2Ffull+%28io9%29
Waterfront property in Timbuctoo.
The engineer behind the construction of the Suez Canal, Ferdinand de Lesseps, gave Roudaire's scheme his blessing, which was all the French public needed to hear, what with de Lesseps being a national hero and all. The French Academy of Sciences pitched in with a special commission and the French government pledged 35,000 francs to get the ball rolling. Most of this was earmarked to send an expedition, led by Roudaire, to North Africa to study the feasibility of the plan.
The London Times said that the plan "dazzles the imagination, yet it has a sufficiently substantial basis to satisfy several shrewd traders in African commerce and some distinguished engineers." The Daily News called the project "the most remarkable that has ever been devised."
This new sea "is sure to be frequented by trading vessels," reported the British magazine All the Year Round, "to carry off the produce of its banks, which will eventually be dotted with groves of date and coconut palms...Hotels, perhaps towns, will spring up on picturesque and eligible sites; luxurious house-boats will float in its most sheltered and shady creeks..."
Roudaire worked tirelessly for the next eight years, but as scientists and engineers gradually turned against the scheme — the former citing bad geography and geology and the latter an expense that had ballooned to over a billion francs — the idea slowly grew out of favor. Not the least problem was the discovery that the chott (a dry salt lake) nearest the Mediterranean was actually above sea level. Roudaire tried to save his scheme by lengthening his canal from about ten miles long to more than a hundred miles while also decreasing the area that would be flooded.
But in spite of all his efforts, the plan was eventually abandoned. Roudaire died not long afterward, at the age of 48 in 1885, of a fever picked up during his final expedition.
Although the Sahara Sea fell out of favor with engineers, politicians and the public, the sheer grandness and audacity of the idea appealed to a best-selling science fiction author. Jules Verne had already alluded to the scheme in his 1877 novel "Off on a Comet!" (a.k.a. "Hector Servadac"), in which he refers the sea as a going concern. But even 30 years later, the idea still attracted him. He describes the construction of the canal in his 1905 novel, "The Invasion of the Sea," as well as the catastrophic creation of the inland sea when an ill-timed earthquake unexpectedly moves the engineer's schedule up.
The idea has never been entirely abandoned, however, and is periodically unearthed. Even the CIA has explored the consequences of flooding the Qattara Depression in Libya. One advantage that intrigues modern engineers is the possibility of generating massive quantities of hydroelectric power. It would require a canal (or a pair of tunnels ,according to one proposal) only 40 miles long to connect the depression with the sea. The drop of 440 feet would be more than sufficient for the generation of power. Concerns over things such as the impact on indigenous peoples and wildlife are among the many major obstacles to these plans.
[Via Archive.org and The Basement Geographer]
http://io9.com/the-great-sahara-sea-that-almost-was-837206551?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+io9%2Ffull+%28io9%29
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