Computer Modeling Shows Ocean Dead Zones Could Last For Millenia, W. Sufficient Warming - AFP

[hatrack]

In a study published online by the journal Nature Geoscience, scientists in Denmark built a computer model to simulate climate change over the next 100,000 years. At the heart of their model are two well-used scenarios which use atmospheric levels of carbon dioxide (CO2), the main greenhouse gas, as an indicator of temperature rise.

Under the worst scenario, CO2 concentrations would rise to 1,168 parts per million (ppm) by 2100, or about triple today's level. Under the more optimistic model, CO2 would reach 549 ppm by 2100, or roughly 50 percent more than today. The temperature rise that either would yield depends on several factors: when the peak in carbon emissions is reached and how quickly it falls, and whether the warming unleashes natural triggers, or tipping points, that enhance or prolong the warming in turn.

Taking such factors into account, the scientists predict a possible rise of around five to seven degrees Celsius over pre-industrial times under the worst scenario. Under the other scenario, there would be warming of roughly between two to four degrees Celsius.

Either scenario spells bad news for the ocean, said Jens Olaf Pepke Pedersen, a physicist at the Technical University of Denmark. Under the worst scenario, warmer seas and a slowdown of ocean circulation would lower marine oxygen levels, creating "dead zones" that could not support fish, shellfish and other higher forms of marine life - and may not revive for 1,500 to 2,000 years. "They would start slowly by the end of this century, it's not something that would happen tomorrow or in the near future but over the next few generations," Pedersen told AFP.

EDIT

http://news.smh.com.au/breaking-news-world/study-predicts-ocean-dead-zones-20090126-7pk2.html

[OKIsItJustMe]

1. The Oceans' Global Warming Hangover

http://sciencenow.sciencemag.org/cgi/content/full/2009/126/3

The Oceans' Global Warming Hangover

By Phil Berardelli
ScienceNOW Daily News
26 January 2009

Even if humans can rein in the atmosphere's carbon dioxide content by the end of this century, large zones in the oceans could remain depleted of oxygen for hundreds or even thousands of years, researchers reveal. The lower oxygen content in the seas--a consequence of global warming--could threaten much of the world's marine life by the 22nd century, including the fish, shellfish, and other creatures on which humans depend for food.

Scientists have known for centuries that warmer water holds less dissolved oxygen: As temperatures rise, oxygen bubbles into the atmosphere. Too little dissolved oxygen and marine life begins to suffocate. Ever since global warming became a concern, researchers have been attempting to monitor the oxygen content of the seas. One such study http://sciencenow.sciencemag.org/cgi/content/full/2008/501/1">last year reported startling expansions of oceanic low-oxygen zones over the past half-century, though part of that development is due to agricultural pollution from streams and rivers. Other research has revealed that once deoxygenation starts, it triggers a feedback loop, wherein a cascade of physical and chemical reactions can greatly prolong its effects.

To determine how long ocean oxygen levels might remain low, Danish researchers constructed a computer model to track the phenomenon over the next 100,000 years. Under Intergovernmental Panel on Climate Change scenarios predicting atmospheric temperature increases of up to 4°C by the end of this century, the resulting ocean temperature increases would expand existing low-oxygen zones, the team reports online this week in Nature Geoscience. That would create so-called dead zones where, for 2 millennia or even longer, few fish and shellfish could survive. These zones would cover tens of thousands of square kilometers in the northern Indian Ocean and in the eastern Pacific Ocean off the tropical coasts of North, Central, and South America. "We were surprised to find how ocean warming and associated oxygen depletion increased more than global warming itself," says lead author and oceanographer Gary Shaffer of the Niels Bohr Institute in Copenhagen.

The bad news doesn't end there. Shaffer says that the model does not take into account the effect of methane released by ocean sediments as the water warms. Methane reacts with oxygen and removes it from water. So it's possible, he says, that the "oxygen depletion would be much worse."

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[jpak]

2. Hey - let's go dump some iron and urea in the ocean!

That'll fix things...

But Good....

:thumbsdown: