Sandy est un avant-goût des choses à venir?

Nous ne devrions pas être surpris. C'est l'avis de nombreux spécialistes du climat qui sondent la destruction causée par le superstorm qui a ravagé le nord-est cette semaine. La fonte des glaces de l'Arctique, l'élévation du niveau de la mer, le réchauffement de l'atmosphère et les changements de conditions météorologiques sont une combinaison puissante susceptible de produire des tempêtes et des raz de marée de l'intensité sans précédent, selon de nombreux experts.

Conscient de la menace, Maire de New York Michael Bloomberg est d'élaborer une stratégie pour atténuer le risque de plus en plus par les tempêtes et les inondations le long de la ville de 500 miles de la côte. Dans une telle zone densément peuplée de tant de l'immobilier cher, entouré par un réseau complexe des estuaires, marées et de l'océan, c'est un énorme défi. Et face à des changements globaux, même une ville aussi inventif que New York ne peut pas tout faire.

Le Groupe d'experts intergouvernemental sur les changements climatiques prévue en 2007 que le niveau moyen de la mer s'élèverait entre sept et 23 pouces d'ici la fin de ce siècle. Projections plus récentes suggèrent que la fonte des glaces de mer pourrait signifier une augmentation de plus de 30 pouces. Le niveau de la mer État de New York Lève Task Force traduit que dans une projection locale de 2 à 5 pouces par les années 2020, et avec de la glace de l'Arctique rapide fondre la hausse pourrait être autant que 5 à 10 pouces au cours des quinze prochaines années. Combinez cela avec une tendance à des tempêtes plus intenses et New York est “très vulnérables,” professeur Michael Oppenheimer de l'Université de Princeton a déclaré à CNN.

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“(Superstorm) Sandy est un avant-goût des choses à venir,” il prédit, “from the combination of bigger storms and higher sea levels, both of which contribute equally to the growing threat.”

New York dodged a bullet by inches last year as the remnants of Hurricane Irene bore down. Ben Orlove, director of the master’s program in Climate and Society at Columbia University, wrote on CNN.com: “Irene also arrived at a time of especially high tides, and its storm surge came within inches of flooding the sea wall. Storms and tides are natural, but sea level rise is not. As it continues, New York grows more vulnerable.”

Oppenheimer, a professor of geosciences, recently modeled the effect of climate change on storm surges for the New York area. In a paper published by Nature in February, he and three colleagues concluded that the “storm of the century” would become the storm of “every twenty years or less.”

New York Governor Andrew Cuomo appears to agree.

“After what happened, what has been happening in the last few years, I don’t think anyone can sit back anymore and say ‘Well, I’m shocked at that weather pattern,'” he said Tuesday.

The conclusion of Oppenheimer and his colleagues is that storms will become larger and more powerful.

“Climate change will probably increase storm intensity and size simultaneously, resulting in a significant intensification of storm surges,” ils ont écrit. Sandy had a diameter of some 900 miles, much larger than most storms.

A study of the New York area in 2010 led by Guy Nordenson, an architect and structural engineer whose offices are in lower Manhattan, concluded: “There is a prevalent risk that the city will be severely paralyzed due to the predicted inundation and wave action associated with storm surge.”

En plus, salt-water intrusion could compromise the quality of drinking water and weaken ecosystems, Nordenson and others concluded in the book “On the Water: Palisade Bay.”

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But the answer, ils soutiennent, is not solely in engineering. “Cities fortify their coasts to protect real estate at the expense of nature … the hard engineering habit has proven costly, unreliable and ineffective.”

Nordenson is serving on a task force set up by Mayor Michael Bloomberg to study ways of giving New York a more resilient waterfront. He told CNN that the region needs a combination of strategies that includes more “soft infrastructure.” New York is losing tidal marshes at a rapid pace, partly because of the rise in sea level but also because of development.

Among the big ideas in “On the Water: Palisade Bay”: create an archipelago of islands and reefs in the New York-New Jersey Upper Bay to dampen powerful storm currents, the islands being “fingered” (with many inlets) and combining tidal marshes and parks.

Nordenson points to the example of the Netherlands and cities like Hamburg that incorporate flood plains into their planning. Similarly Hurricane Katrina showed the importance of preserving Gulf coastal swamps. He hopes a project with the New York Port Authority to begin using dredged material for natural barriers will get underway soon.

Nordenson and his team of engineers, architects and designers showed some of their ideas at the Museum of Modern Art for an exhibition called “Rising Currents.”

At the local level, the Nature Conservancy is working with communities in Long Island to identify the risks from rising sea levels and protect wetlands. Sarene Marshall, who leads the Conservancy’s Global Climate Change Team, estimates that every dollar spent in preventive measures saves $5 in disaster recovery, and that long-term investment in natural infrastructure is more effective than hard engineering. She points to the value of the humble oyster reef, nature’s version of the sea wall.

Paul Greenberg, écrit dans le New York Times mardi, fait écho à son point, dire que dans les siècles précédents “une population de bivalves qui comptait en milliers de milliards … joué un rôle essentiel dans la stabilisation de la rive de Washington à Boston.”

Conservation de la nature estime ces récifs peuvent réduire les risques de tempête pour 7 million d'Américains vivant sur la rive.

Mais îles, huîtres et d'autres mesures visant à atténuer les ondes de tempête peuvent pas isoler de New York à partir des tendances des milliers de miles dans l'Arctique. Un nombre croissant de preuves relie la disparition de la couverture de glace de l'été dans l'Arctique à l'évolution des conditions météorologiques.

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Au cours des trois dernières décennies, sur 1.3 million de miles carrés de glace de mer arctique a disparu, équivalent à 42 percent of the area of the lower 48 états.

Climate models previously projected that the Arctic might lose almost all of its summer ice cover by 2100, but some scientists believe the trend is now accelerating and that it will be gone long before then.

“In addition to the extent of sea ice, what remains is thinner than it used to be,” said Walter Meier of the National Snow and Ice Data Center at the University of Colorado.

Less sea ice means warmer water. Sea surface temperatures off the coast of the northeast United States are now the highest ever recorded.

“It’s like leaving the fridge door open,” said Meier. The only way to restrain the process would be to moderate temperature increases, which in turn would depend on lowering carbon dioxide emissions.

Jennifer Francis at the Institute of Marine and Coastal Sciences at Rutgers University has shown that a warmer Arctic tends to slow the jet stream, causing it to meander and in turn prolong weather patterns. It’s called Arctic amplification, and it may be helping entrench drought in the northwest United States and lead to warmer summers in the Northern Hemisphere.

But there may be another effect.

“Larger swings in the jet stream allow frigid air from the Arctic to plunge farther south, as well as warm, moist tropical air to penetrate northward,” Francis wrote in Yale University’s Environment 360 blog. That’s pretty much what happened this week, a spectacular collision of Arctic and tropical weather fronts.

A recent article in the journal Oceanography shed more light on the consequences of Arctic ice melt. Charles Greene at Cornell University and others wrote that fundamental changes in the behavior of the jet stream will “stack the deck in favor of severe winter weather outbreaks in the United States and Europe into the foreseeable future.”

Given the scale of the challenge, Oppenheimer and others believe there needs to be urgent remedial action to mitigate the effects, such as raising subway entrances and reinforcing the lower floors of buildings. At the moment, Oppenheimer said, there’s a lot of evaluating hazards and too little action to address them.

After a sudden deluge in 2007 that closed part of the subway system, the New York Metropolitan Transit Authority committed more than $30 millions de soulever les grilles de ventilation et de redessiner les entrées de certaines stations de métro. Il a également passé en grande partie sur les pompes, mais une hausse substantielle serait bientôt surmonter les mesures correctives. Et à côté des lignes de métro, transformateurs de puissance et des réseaux de fibres optiques sont vulnérables aux inondations.

Actions plus ambitieuses auraient de lourdes conséquences politiques et économiques. Niveau de la mer Rise État de New York Groupe de travail a été créé en 2007 et rendu son rapport à l'Assemblée législative sur le dernier jour de 2010. Parmi ses principales recommandations était plus grande dépendance sur la protection naturelle comme les marais et un resserrement des règlements de zonage pour éviter la perte de ces fonctions.

New York City n'est pas d'accord avec les recommandations les plus critiques de l'écran, dire qu'ils ont fait “ne pas reconnaître les différences entre les zones sous-développées et les villes densément peuplées.” Propre groupe de travail de la ville a rejeté l'idée de limiter le développement comme un coût prohibitif.

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Douglas Hill, de l'onde de tempête Research Group de l'Université Stony Brook a proposé une chaîne de massifs barrières de la mer à Long Island Sound qui pourraient être fermées pour prévenir les inondations à chaque fois une onde de tempête menace. On serait près du pont Verrazano Narrows. (La barrière de la Tamise à Londres effectue un tel rôle de façon plus modeste.) Mais le coût dépassera probablement $10 milliard; un obstacle dans le coût de Venise $7 milliard.

Parmi les autres options: des règlements plus sévères sur le cas des installations industrielles et chimiques peuvent être situés, l'amélioration de la conception des bâtiments pour faire des niveaux inférieurs inondations preuve (connu sous le nom de franc-bord dans le secteur de l'assurance) et “bords souples” que l'action des vagues mieux de rupture.

Stronger and maybe higher seawalls around more vulnerable parts of Manhattan might also help. The current seawalls are about 4 à 5 feet above the average sea level. Many were built at the beginning of the last century. A New York Times article from August 1901 marveled at “The Massive Sea Wall Which Will Encompass Manhattan.”

“It will be many generations, perhaps centuries, before the wall … will have to be rebuilt or will even require any extensive repairs,” the Times reported then. That was before climate change became part of the lexicon. New York City’s “Vision 2020” plan warned that sea walls and other shoreline structures are likely to need more frequent repair because of more damaging storms.

Whether Sandy will drive the issue of climate change up the political agenda seems doubtful. According to a recent Pew Research Center poll, 67% of Americans believe the Earth is warming, up slightly since 2010, but that’s 10 percentage points less than in 2006. Among both Democrats and Republicans, the percentage has declined, as has the number (maintenant 64%) who say it’s a serious problem.

Sarene Marshall of the Nature Conservancy says the lack of debate about climate change in the presidential election campaign has been “unfortunate,” but believes that Americans are getting to the point of recognizing what they see for what it is.

Source: CNN