Friday, May 14, 2010

How Big is a Big Bad Oil Spill?

Let's start with something we can all agree on: the oil spill in the Gulf is bad.

But how big is bad? How does this spill compare with spills in the past? And what happens if, and when, it surpasses the size of the 1989 Exxon Valdez? It turns out, in the media's preoccupation with measuring this spill against the Exxon Valdez, reporters may have distorted the actual history (and frequency) of catastrophic oil spills.

To begin, we need to know how volumes of oil are measured. Unfortunately, this volume is measured in a variety of ways, and the media shows no consistency in the units they report.

First, there's a gallon. We know gallons because we fill our gas tanks in gallons. We also buy milk in gallons. A gallon of oil fits in here:

Oil is also measured in barrels. Oil was actually shipped in barrels in the 19th and early 20th centuries:

(Image courtesy of the Library of Congress's American Memory digital archive.)

In reality, the actual size of oil barrels varied. In the 19th century, crude oil was poured into whatever was available, regardless of the size. Eventually, though, the standard American barrel of oil came to contain 42 gallons.

Finally, especially in international contexts, oil quantities are often reported as tonnes, or metric tons. This is actually a measure of mass: 1 tonne = 1,000 kilograms. It's just one more way to add to the confusion. How many tonnes are in a barrel varies depending on what's in the oil and where it's produced: some oils are thick and heavy, others light -- you can find many conversions for specific countries and years here. The global average is about 7.3 barrels per tonne; you can find a calculator here.

Confusingly, in coverage of the Gulf spill, reporters have been using both barrels and gallons, even while reporting for the same news organizations.

What does this mean for the Gulf spill? Initially, BP reported the leaks amounted to about 1,000 barrels per day -- that's 42,000 gallons. By April 28, government estimates pushed that figure up to roughly 5,000 barrels per day -- or, 210,000 gallons.

And to make matters worse, today, NPR reported revised estimates that put the spill at between 56,000 and 84,000 barrels (that's 2,352,000 to 3,528,000 gallons). This criticism was similarly voiced in the New York Times, which went on to note how bad things might still get:

BP later acknowledged to Congress that the worst case, if the leak accelerated, would be 60,000 barrels a day, a flow rate that would dump a plume the size of the Exxon Valdez spill into the gulf every four days. BP’s chief executive, Tony Hayward, has estimated that the reservoir tapped by the out-of-control well holds at least 50 million barrels of oil.

For most of us, these big numbers start to lose their meaning. And here's where history comes in. The Times' reference to the Exxon Valdez is representative of many news organizations, which seek to put the size of this leak into perspective. We can't easily imagine how much oil is contained in thousands of barrels (or gallons), but we all remember the 1989 disaster of Exxon Valdez, which ultimately dumped about 270,000 barrels (11,340,000 gallons) of crude oil into the sea. The images out of Valdez have become iconic, with some 270,000 birds killed.

But was Exxon Valdez the worst oil spill in history?

Not by a long shot. Since 1967, it ranks as only the 35th worst spill. The actual worst was in 1979, when the Atlantic Empress sank off Tobago in the West Indies, spilling some 2,104,000 BARRELS into the water: that's over seven and a half Exxon Valdezes. The ABT Summer, 700 nautical miles off the coast of Angola was a close second in 1991, spilling 1,906,000 BARRELS. The list, as you can see goes on:

(Graph courtesy of the International Tankers Owners Pollution Federation's 2009 Oil Tanker Spill Information Pack -- the red is the relative size of the Exxon Valdez.)

Most Americans have never heard of The Atlantic Empress, ABT Summer, Castillo de Bellver, Amoco Cadiz, or any of the other largest spills. That's probably because they took place far from the United States, either in deep water or somewhere without much US press coverage:

The Exxon Valdez was a tragedy, but in the United States, it has so grossly overshadowed much larger and more catastrophic spills. The Exxon Valdez has become so widely known because it was so close to shore, affecting so many Americans, and producing such disturbing images of oil coated wildlife. But much more oil has spilled into the world's oceans with less outrage but no less an ecological consequence.

This won't come as much comfort, of course. The Gulf catastrophe is a leak, not a spill, and it will keep pouring oil into the water until it's plugged. The real problem is that so many spills have gone unnoticed for so long -- and until now, we've actually had a pretty good decade.

1 comment:

  1. Thanks, Pete!

    Western Europe seems to have suffered the lion's share of these big spills. Can you provide any insight into the long-term consequences of some of the big spills? Such as shoreline accumulation, or disruption to the food chain? Any impact on local fishermen, shipping, etc?