11 Apr 2015

Mixed news on greenhouse gases

6:59 am on 11 April 2015

The Ministry for the Environment (MFE) has published a lengthy report summarising New Zealand's greenhouse gas emissions from 1990 until 2013.

The year 1990 was chosen because that was the starting date for calculating emissions of carbon dioxide, methane, nitrous oxide and other gases under the Kyoto Protocol.

The accumulation of these gases in the atmosphere can cause climatic changes such as global warming.

The report found the total volume of those gas emissions rose from 66.7 million tonnes in 1990 to 81.0 million tonnes in 2013.

The biggest contributor to the problem was agriculture, due mainly to emissions of highly potent methane from livestock belching and flatulence.

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Photo: 123RF

It also stemmed from the release of even more potent nitrous oxide from the soil.

The second largest contributor was the transport sector, chiefly carbon dioxide-laden exhaust fumes from vehicles.

The report said the total size of New Zealand emissions was not the only issue.

The total figure needed to be qualified by the ability of trees to absorb carbon dioxide as they grew, in order to give a reliable clue about how much carbon dioxide accumulated in the atmosphere in real terms.

This figure is the net figure on emissions, and because New Zealand has a lot of forests, the figure for net emissions is pulled down to 38 million tonnes in 1990 and 54.2 million tonnes in 2013.

More trees planted - but even more milled

The report attributes this to intensive tree planting in New Zealand between 1992 and 1998.

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Photo: 123rf

But this trend was later reversed and since 2008, more land has been taken out of forest than was put into forest.

Environmental critics say this will make it difficult to offset future emissions, and the problem could get worse when the trees that were planted from 1992 are harvested for their timber.

But the MFE report and a related report from the Ministry for Business Innovation and Employment have positive things to say as well.

They say the electricity industry produces far less carbon dioxide per watt of electricity than it used to.

Agriculture has also improved in relative terms, and economic growth overall is less environmentally costly than it used to be.

It says the total growth in emissions from 1990 came on the back of strong economic and population growth but that growth was faster than the growth in emissions.

The report says New Zealand today produces only two-thirds of the greenhouse gases that it did in 1990 for every dollar of national wealth that it creates.

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