Deepwater Horizon: a “natural” disaster?

Rush Limbaugh’s comment about the Deepwater Horizon oil gusher has been widely mocked in the blogosphere. “The ocean will take care of this on its own if it was left alone and left out there,” Limbaugh said. “It’s natural. It’s as natural as the ocean water is.” (

Just how wrong is Limpbaugh, anyway? Let’s look into it. First of all, there is a lot of natural seepage of oil from the ocean floor, so he’s got a point there. A 2003 article from GeoMarine Letters estimates global natural seepage of crude oil into the ocean at 600,000 metric tons/year, although there’s a wide range of uncertainty. This is a bit less than half of the total oil spilling into the oceans currently; the rest we owe to human activity.

What happens to all that oil? A lot of it apparently stays on the bottom, as it’s pretty dense; much of that is consumed by bacteria. So Rush is right that there are natural processes to deal with it.

However, those oil-eating bacteria consume oxygen from the water while dealing with the oil, so the environment around a big spill is not too hospitable for other forms of marine life.

As has been widely noted, the current gusher is releasing a lot more than the official estimate of 5000 barrels a day – more like 25,000 to 80,000.

So how does this current “leak” compare to the natural leakage?

Some calculations are in order.

First, a barrel is .1192 cubic meters of oil.

Crude oil has a density somewhere around 800-900 kg/cubic meter (varies). Call it 850.

And let’s estimate somewhere in the middle range for the size of the “leak” – 50,000 barrels/day.
That means the Deepwater Horizon is pouring 5066 metric tons of oil per day into the Gulf.

At that rate, as of today, it has already poured 1/5 of a year’s global natural leakage into one small part of the Gulf of Mexico. Left uncapped for a total of 118 days, it will have dumped a full year’s worth. And considering that the natural leakage is about equal to the average human-caused leakage, another way of looking at it is that this single accident could double the typical year’s worldwide artificial oil leakage by August 18th.

Think that it’s unlikely to continue this long? The previous record-holder for an offshore oil “leak” was the Ixtoc I well off Campeche, which spilled about 20,000 barrels a day for 290 days in 1979-1980 before it was capped. And that one was in only 50m of water rather than almost 2000m, making it technically much easier to deal with.

Now, Rushbo, it’s true that eventually natural processes will deal with this – but the environment of the Gulf of Mexico is going to be profoundly altered by this spill for a long time to come, even if they cap it completely today. The “dead zone” around the mouth of the Mississippi is going to grow enormously, and some of the most important fishing waters around our continent are going to be producing mainly oil-eating bacteria instead of shrimp, oysters, and redfish, probably for years. And I bet even Emeril can’t make a tasty etoufee out of oil-eating bacteria.

So, Rush has his facts right, but the implications totally wrong. It’s a bit like saying that there are traces of cyanide in almonds, and they don’t hurt you, so it’s okay to eat cyanide by the spoonful. Quantity matters, and this catastrophe is huge.

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