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cows and carbon sinks


Felix Grant explores the application of statistical software in carbon emissions


n externality, to an economist, is[1] ‘a side-effect or consequence ... that affects other parties without this being refl ected in the cost of the

goods or services involved’. Externalities take all sorts of forms, and can be positive or negative, but over the past half-century industrial pollution of the environment has become the primary exemplar. More recently still, the focus has

narrowed down to carbon-based compounds whose costs are paid in a number of ways. The crudest direct health effects are usually localised, and become a matter for local legislation or lack of it; the atmospheric greenhouse effect is a global issue with no respect for human jurisdictional boundaries. Attempts to deal with pollution almost

always come down to mechanisms designed to convert an externality into a direct cost

Musselling in on the action A recent study[9]

by Gaylord and others, using

JMP statistical analysis software, investigated the likely effects of anthropogenic carbon dioxide on the Californian mussel, as an exemplar of the impact on key foundation species. Numbers of mussel larvae were cultured in seawater with varying carbon dioxide concentrations, from the mean present day 380 parts per million (ppm) level to the 970ppm upper estimate bound for the end of this century. The resulting data showed a clear and


paid by the polluter, and carbon is no exception. A number of schemes exist to license carbon emission, with a market in which those who emit least sell permissions to those who emit most, thus exerting a direct proportional cost pressure on producers. Whether this method is effective, and if so

signifi cant statistical association between rising carbonifi cation and declining larval shell size, strength and thickness. There was also a negative correlation with tissue mass.

Analysis also suggested two modelled scenarios for consequential impact: continued development of larvae at the present rate or a slowed development rate achieving the same end shell mass over a longer period. Either model produces greater vulnerability in this crucial development phase, reducing species viability.

to what degree, is a subject of considerable political argument; but it remains the principle approach. Its use depends on quantifi cation of emissions, which is neither simple nor straightforward. In practice, output is usually simplifi ed from the full gamut of emitted substances (not all of them carbon based) to a single carbon dioxide equivalence fi gure, the product of mass and a radiative forcing factor, which varies from substance to substance. But that still leaves an impractically large data acquisition and monitoring task. The essence of statistical data analysis,

always and everywhere, is generalisation from sample to population with a quantifi ed level of confi dence. Sometimes, as with extraterrestrial exploration in the last issue, this is because only tiny amounts of data can be captured and the maximum information must be squeezed from it. In the case of planetary emission levels the

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