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Public Radio's Environmental News Magazine (follow us on Google News)

Ocean Extinction Trend

Air Date: Week of

Increased atmospheric carbon is causing a “Deadly Trio” in the world’s oceans. Alex Rogers is Scientific Director of the International Program on the State of the Ocean. He told host Bruce Gellerman that the trifecta of global warming, ocean acidification, and deoxygenation have been associated with all of the five major extinction events in paleontological history. Photo--Excess carbon absorbed by the ocean leads to acidification and coral bleaching. (Wildsingapore)


GELLERMAN: Scientists have long known that our oceans are in deep trouble, but now they’re issuing a dire warning of a rapid mass extinction of sea life. Marine experts meeting in Oxford, England were surprised to find the rate of change is accelerating unlike anything that’s happened in the last 55 million years. They blame carbon dioxide emissions in the air for a deadly trio of factors that are disrupting the seas. The International Program on the State of the Ocean convened the meeting - conservation biologist Alex Rogers is scientific director of the organization.

ROGERS: This report really is a mixture of despair and hope. If you look back in past extinction events in the oceans, they’re all associated with a major disturbance of the carbon cycle or carbon system of the Earth. And the symptoms of that are warming, ocean acidification, and also deoxygenation of the oceans. Now today we’re certainly seeing warming, particularly in polar regions. We’re seeing acidification taking place in the oceans at a staggering rate.

GELLERMAN: So global warming, ocean acidification…what’s the third?

A map of low oxygen dead zones around the world. (Robert Diaz, Virginia Institute of Marine Science)

ROGERS: The third one is deoxygenation.


ROGERS: Yeah, hypoxia. Essentially, warm water contains less oxygen than cold water. But also, in modern times, we’re seeing deoxygenation occurring through essentially nutrient runoff from land, and this is coming from the use of fertilizers in intensive agriculture and sewage and so on, which has been poured into the oceans. That causes a bloom of algae, which then die, and they’re broken down by bacteria, which use up the oxygen in the water column.

GELLERMAN: So essentially we’re killing our ocean.

ROGERS: The sheer rate of CO2 input into the atmosphere and the changes that they’re driving is almost completely unprecedented in terms of past history.

GELLERMAN: The oceans are carbon sinks. I mean, they’re designed - they’re supposed to - operate as absorbers of carbon and maintain the balance, right?

ROGERS: That’s absolutely right. The ocean’s been doing this fantastic service for us of mopping up about a third of the emissions that we’ve been producing through industry and land use and so on, but there’s a cost to that and this again links this rate at which this is happening. If this was happening slowly, the weathering of rocks and so on would be naturally neutralizing the carbonic acid that’s produced when the oceans absorb CO2 - but because of the rate at which we’re dumping CO2 into the atmosphere, the oceans simply can’t neutralize that sufficiently quickly so the oceans are acidifying at a staggering rate.

GELLERMAN: So in terms of paleological time, how does this compare, say, with what happened in the past?

ROGERS: Well the nearest analogy we could find to this in the past is the Paleocene-Eocene Thermal Maximum, which was about 55 million years ago. During that period, there was a mass extinction - it's not one of the Big Five, so it’s not at the same scale of the end of the dinosaurs, for example - but it still led to the loss of up to 50 percent of marine species in some groups of organisms. The difference is that at that time it’s estimated, through natural causes, just over two gigatons of carbon was being pumped into the atmosphere per year for several thousand years. Now we are pumping 30 gigatons of carbon into the atmosphere per year. So that’s why what’s happening now is so extraordinary - it's simply the rate at which this is occurring.

GELLERMAN: So are you expecting to see mass extinction - is the ocean going to collapse?

Coral bleaching (Ove Hoegh-Guldberg)

ROGERS: Well, we thought long and hard about this and we’re seeing very severe impacts from climate change already. Since the 1970s, we’ve seen mass coral bleaching events taking place. In 1998, a single bleaching event - and these occur as a result of elevated sea temperature - wiped out 16 percent of all the world’s tropical coral reefs. One event! Those events would increase in frequency as temperature increases. And I’ll just add, coral reefs are our most diverse marine ecosystems. They host – we’re not sure how many species - there are estimates everywhere from half a million to nine million species. And those ecosystems are in danger of collapse, probably within a generation and certainly by the end of the century if we continue to emit CO2 at the same rate that we’re doing now.

GELLERMAN: Okay, well Professor, cheer me up. The good news, please?

ROGERS: The hope is that marine species have been remarkably resistant to extinction. We know that overfishing has had massive effects on fish populations - you know, many of them have been reduced to 10 percent or less of their original size. But those species are still there. And in fact, the ocean still harbors much of its biodiversity that it’s harbored for millions of years. So if we act very quickly and we act decisively, we do have the opportunity to divert this disaster and really change this trajectory of degradation of these species and these ecosystems, upon which we really depend.

GELLERMAN: How wide is the window of opportunity - what are we talking about here?

ROGERS: We’re talking about 10 years - 10 to 20 years.

GELLERMAN: Whoo! That’s a short fuse.

ROGERS: It’s a very short fuse - the windows for action are really very, very narrow indeed.

GELLERMAN: We’ve been talking to Alex Rogers - he’s scientific director of the International Program on the State of the Ocean. Professor Rogers, thanks so much.

ROGERS: Thanks very much for listening, thanks.



Report on the “Deadly Trio” of ocean threats

International Program on the State of the Ocean


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