How Climate Change Is Killing Our Oceans

By Douglas Fischer, Daily Climate. Posted November 12, 2008.

The most pressing example of climate change's impact is not monster hurricanes, retreating glaciers or water wars. It's the humble swimming sea snail.

The tiny pteropod has difficulty growing a shell in a warmer planet's acidified ocean waters. Given the snails' role at the base of the cold-water food chain, its struggle threatens the entire polar ecosystem, through salmon to seals and whales.

The problem is one of many associated with ocean acidification. That change is well underway -- a consequence of warming that has already happened and fossil-fuel emissions that have long since been dumped into the atmosphere.

In absorbing those emissions the oceans have buffered humanity from the worst effects of climate change. But in doing so ocean chemistry has changed, acidifying to levels not seen in 800,000 years.

The result, according to a new report issued by Oceana, is that today's ocean chemistry is already hostile for many creatures fundamental to the marine food web. The world's oceans -- for so long a neat and invisible sink for humanity's carbon dioxide emissions -- are about to extract a price for all that waste.

The effects are not local: Entire ecosystems threaten to literally crumble away as critters relying on calcium carbonate for a home -- from corals to mollusks to the sea snail -- have a harder time manufacturing their shells. Corals shelter millions of species worldwide, while sea snails account for upwards of 45 percent of the diet of pink salmon.

To avoid the most serious problems associated with acidification, Oceana and other scientists warn, society must hold atmospheric carbon dioxide levels at 350 parts-per-million, roughly 25 percent higher than the pre-industrial mark.

The rub is that the globe has already passed 385 ppm. And many economists and climatologists figure the peak will lie somewhere north of 570 ppm before society figures out how to curb emissions.

"Climate change has been happening for a long time," said Jackie Savitz, Oceana's senior director of pollution campaigns and co-author of the report, Acid Test: Can we save our oceans from CO2? The oceans "are so big, so vast, and everyone thought they were untouchable. But the fact is we've been touching them all along."

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What alarms scientists most is the rate of change: The transformation has happened over 250 years, faster than anything in the historical record. And if emissions remain unchecked, Oceana warned, the oceans in 40 years will be more acidic than anything experienced in the past 20 million years.

Over the next several centuries the pH changes may be larger than any inferred from the geologic record of the past 300 million years, with the exception of a few rare extreme events, scientists predict.

The process is fairly simple. For eons prior to the Industrial Revolution, oceans were at equilibrium with the atmosphere, absorbing as much carbon dioxide as they released.

As humanity started burning fuel, atmospheric carbon dioxide levels started to rise, and the oceans responded, taking in more and more carbon each year and increasing acidity by nearly 30 percent.

The oceans so far have absorbed some 30 percent of the carbon dioxide that humans have added to the atmosphere since the beginning of the Industrial Revolution and nearly 80 percent of the heat generated by those gases, according to Oceana.

Today the world's oceans absorb some 30 million metric tons of extra carbon dioxide every day, according to scientists -- roughly twice the amount of carbon dioxide emitted each day by the United States.

The ocean has a number of natural buffers to help with change -- ocean sediments and deep water represent two enormous potential reservoirs -- but they all work on vastly slower time scales, said Richard Zeebe, associate professor of oceanography at the University of Hawaii at Manoa.

"It's very difficult to find a nice analogue in the past that's going to show what we're going to experience over the next 200 to 300 years," he said. "It's pretty much outrageous what we've done."

"We are overwhelming the system," he added. "The system is not quick enough to react. It takes thousands of years to do this."

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Scientists are already seeing harm as the oceans acidify. Reefs are struggling in many parts of the world, shell growth rates are slowing, life phases -- particularly reproductive maturity -- are being thrown out of whack.

See more stories tagged with: global warming, climate change, oceans, ocean acidification

Douglas Fischer is editor of TheDailyClimate.org.

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