Sequestering carbon in the ocean is hard to do, and even harder to measure

A new paper by Wilmers et al. in Frontiers in Ecology and the Environment, which features a neat analysis of how carbon uptake in kelp forests is affected by the sea otter population, illustrates the likely folly of creating a carbon credit business through fertilizing the ocean with iron, the science and environment scandal of the month.

The proponent of the iron dumping off Haida Gwaii last month, Russ George, claims to be a hero who is trying to fight climate change. Most other observers see him as a businessman hoping to raise money selling carbon offsets or carbon credits.

It is hard to see how this could ever become a credible business. In order to sell carbon credits, you’d to:

a) need to prove fertilizing the ocean with iron does lead to long-term storage of carbon in the deep ocean, an open question discussed in my previous post,
b) be able to measure how much carbon was stored

Even if (a) is proven correct, the accounting problem (b) remains.

This is where the Willmers et al. paper comes in. Kelp forests, common on the west coast, are among the most productive marine ecosystems, sucking carbon out of the atmosphere at high rates. You haven’t been diving until you’ve had to unravel yourself and your gear from metres long strings of kelp. Willmers et al. calculates that kelp forest store about ten times more carbon if sea otters are present, because without the otters eating the urchins, the urchins eat all the kelp. As such, there could be a carbon incentive, and potentially a market, to maintaining healthy otter and kelp populations (no easy feat).

The problem? Just as in the iron case, it’s really hard to measure how much of the carbon taken up by the kelp gets exported to the deep ocean, where it would be sequestered long-term. Since there’s no precise data, the authors provide estimates of carbon export over a range of 1% to 50% of the kelp carbon uptake. This no fault of the authors: deep carbon export from productivity on the surface is hard to measure and predict, so they’ve chosen an uncertainty range. The huge range is reasonable for the discussion section of a paper on carbon uptake in kelp forests. But it won’t fly with accountants who need to sell the carbon credits.


Via Simon’s Maribo Blog


  1. Pingback: Another Week of GW News, October 28, 2012 – A Few Things Ill Considered

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