Nick Smith’s statistical massage

by frog

This is one of the slides used by the Minister for the Environment in the climate change target consultation presentation.

Click for larger image.

The bar graph showing percentage emissions change for sectors between 1990 and 2007 serves to focus attention on the electricity sector, where the emissions have grown over 90% in that time.

But astute readers will notice that the energy half of our emissions is broken down into sub-sectors (electricity, transport, etc.), while the agriculture half is broken down into gases. Why the double-standard? It’s partly technical, but it serves to hide some key areas of emissions growth that we need to deal with.

If you break agriculture into its sub-sectors, you are confronted by the sacred cow of New Zealand ghgs – the large increase in emissions from dairy farming.

You see, the modest looking 12% increase in agricultural emissions is made up of a large increase in dairy emissions, offset by significant decreases in emissions from sheep and beef cattle.

I checked the inventory and discovered that the increase in dairy emissions of enteric methane alone is 70% over the 1990-2007 period, about the same rate of increases as transport emissions, and not much less proportionally than electricity. (Unfortunately the inventory doesn’t break-down all ag emissions into sub-sectors so I don’t know how much NOx comes from dairy rather than sheep, for example.)

More importantly, the real increase in dairy methane emissions is 3.5MtCO2e, which is MORE than the real increase in electricity emissions of 3Mt – in fact, the difference is even greater because the dairy number is only methane (and NOx has increased much more than methane). So, in real terms, the increase in total emissions from dairy farming may well be nearly twice that of the increase in electricity emissions.

The structure of the graph means that one source is accentuated and another hidden: while the pie graph above indicates the relative proportions of each sector, the bar graph above only accounts for relative increases. A better graph is one that combines the two, such as this one in the inventory:

Click for larger image.

However, this doesn’t split energy and agriculture into sub-sectors, so it still hides the large increase in dairy emissions is hidden in the broad agriculture category. Hiding it in the statistics only delays dealing with it. I guess I’ll have to do my own…

Fortunately, the Minister did stand up to those who sought to completely ignore the science and significance of ag emissions at the Napier meeting last night.

Addendum: No Right Turn has crunched the numbers and done the graph I was seeking. Thanks.

Click for larger image.

frog says

Published in Economy, Work, & Welfare | Environment & Resource Management by frog on Thu, July 16th, 2009   

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