Monday, July 12, 2010

How much plastic is in the ocean? (Reposted)

Nobody knows for sure, but the new estimate - 315 billion pounds - posted at 5 Gyres is surely wrong.

You know that the estimate is going to be bad when the author, Stiv Wilson, starts out with this sentence: "If we were to attempt to quantify how much is out there, we need to do some big math." Watch out! Big math is coming! Danger! Danger!

Stiv starts with a measurement of 5 kg/km2, derived from drag net measurements taken in the North Atlantic Gyre, and also states that plastic pieces can be found 90 feet down. Good. Data is always a good spot to start with.

However, Stiv takes this value of 5 kg/km2, taken from a gyre, an known area of concentration and multiplies it by the entire surface area of oceans on the earth, completely overlooking that most of the areas are of lower concentration, since they are not gyres or "garbage patches".

But it get worse. 90 feet worse. Stiv further makes that assumption that the concentration above is for the first foot and then multiples it by 90, as if the plastic is uniformly distributed for all 90 feet. The assumption of uniformity is not rationalized at all. I would strongly propose that the uniform assumption is going to be inaccurate and overstates the amount of plastic. Just the fact that a number exists as a lower limit strongly suggests that it is an asymptote, a depth below which plastic is so seldom seen as to be nonexistent. If 90 feet were not an asymptote, there is no reason why 90 feet would be a cutoff at all. Plastic should be found at all depths if it were uniformly dispersed. Lacking data, all sorts of concentration-depth profiles could be proposed - linear, exponential decay, a power law fit or whatever. Regardless of the model, the end result is again that Stiv has overestimated the amount of plastic.

Now the real kicker: Stiv calls these "conservative estimates". Opps, sorry, I misquoted him. Shame on me. He doesn't call them conservative estimates afterall. Instead, he calls them"extremely conservative estimates".

So know we all know how bad "big math" can be, which in the end turned out to be merely the product of 3 numbers.

Look, plastic has no business being in the ocean, but to overinflate estimates of how much their is has no value to anybody.


stiv said...

John, sorry to get you so riled up! You need to look at Giora Proskurowski work, that shows the mixed layer ending at 32 meters, based on this computer model for characterizing plastic mixing due to sea state. His data explicitly shows that plastic mixes in this water column, not uniformly, but he finds similar concentrations at different depths.

Now, let's talk about how gyres behave. You need to look at Curtis Ebbesmeyer's data that shows that upon each orbit of the North Pacific Gyre, half the contents are cast out to either re-enter another gyre, or eventually be washed up. This would indicate that that half the plastic in the ocean isn't in the gyres. Also, you're going to need to look at drift buoy data that explicitly shows that some gyres concentrate more than others. I've been to the lat and long that Giora's sampled and it's not the epicenter of the North Atlantic Gyre.

Also, take the 1992 EPA estimate of 14 billion tons of garbage per year dumped into the ocean. Half of it is synthetic. Multiply this by 40 years of plastic consumption on a widescale and adjust for population growth and plastic consumption growth.

Then you get 280 billion pounds. Is that a better number?

Again, the point here isn't to quantify absolutely how much plastic is in the oceans, but it's meant to give an idea.

John said...


Glad to see you can provide more data, but you are still making a mess of the whole analysis.

Regarding Proskuowski's work, a computer model does not generate data, rather results, so it does not "explicitly show" anything. Results are then interpreted by humans to reach conclusions.

And what pray tell, is the meaning of "not uniformly, but he finds similar concentrations at different depths."? Further, if he has such results, why did you not use them in your original post? It would be straight forward to use integral calculus and incorporate the results.

Further, I cannot see any published results from Proskurowski that are relevant. Look at this. What am I missing?

And is this another example of "big math"? "... take the 1992 EPA estimate of 14 billion tons of garbage per year dumped into the ocean. Half of it is synthetic. Multiply this by 40 years of plastic consumption on a widescale and adjust for population growth and plastic consumption growth." Let me see, 14 billion x 40 years = 560 billion, but you cut it in half to since half of it is synthetic (all of these numbers are unreferenced, so even their validity are open to question, especially given that they are nearly 20 years old).

My point is this: there are a lot of people with a far better understanding of this problem that have not calculated any such estimates because they know they would have to make so many assumptions that the results would be meaningless and showing such doubious results would hurt their reputation as researchers. For instance, the Scripps Institute doesn't even know the size of the Pacific Gyre and have clearly stated such.

So why do you persist in this game?

stiv said...

Ahh, sure-- you're still missing the point--- I'm not looking for straight quantification here. I'm looking for context. And if you want to know precisely why, several industry groups are funding people who say they can cleanup the gyre. My project is to show that the scale is too big to do it.

The problem here is that data doesn't work. There are only 'ball parks.' because every time it rains or the wind blows on this planet, plastic enters the ocean-- there is no real way to monitor it.

I understand your concerns, but you really need to look at the spirit of the post. Also, I've been out there looking at plastic over 3,000 miles, everywhere, in the Atlantic, In the Indian, and this fall in the South Atlantic.

Believe me, there is no money in being an activist. I'm concerned with this issue greatly because what I've empircally observed is more than can ever be cleaned up and I can't stand by watching snake oil sold by an industry that doesn't take responsibility for their environmental footprint.

Travel the world, look at waste streams, look at rivers in egypt, look at garbage dumps in the azores, look at waste management in Indonesia, I think you'll agree that we're in the 100s of billions of pounds, especially since nothing is being done to mitigate it.

And no, there are not lots of people with a 'far better understanding of the problem-' and if you asked anyone from Scripps, I guarantee that they'd give you billions and billions like I did.

John said...

Glad to see you finally ditched the math. The problem is, others have picked up on your calculations and repeated them as truth instead of being "context". Google "plastic ocean supertankers". Your 315 billion pounds now has over 200,000 hits. Your "big math" now has a life of its own.

Numbers are not neutral. People put value on them, emotional value, and any report with a number attached to it has more perceived "truth" than one without, even when the number is utter nonsense.

Now that you've given up on the calculations, will the next posts in the series be void of calculations, or will you continue with the charade? Will you be upfront that the numbers are only "context"?

Anonymous said...

So John, you are so very much against the calculations of Stiv Wilson. I wonder if you have tried to come up with a figure yourself?

Or if putting an emotional connection to the plastic pollution in the ocean not something that is in your scope of criticism.

So, lets say that Stiv is terribly wrong and there are not 142 billion kilos of plastic waste floating in the oceans; tell us, what is your estimation.

Something that can not be quantified can not be managed.