View all publications

8 Discussion

8.1 Wood as carbon neutral

The analysis to this point has assumed that all sources of greenhouse gases contribute to the total emissions. In particular, solid fuel used for home heating has been ascribed a significant amount of CO2 emissions. However, in the current carbon accounting systems, biofuels such as wood are considered renewable and carbon neutral. That is it is assumed that the wood consumed is replaced with new growth. This has made the increased use of wood a popular option for reducing CO2 net emissions. However this can be an overly simplistic assumption since it is not a given that wood consumed will be replaced with like wood. Alternative scenarios include (a) the wood consumed is not replaced but the land cleared ends up being used for other purposes, (b) heavily forested land (with high carbon sequestered amounts) is cleared for more lightly grown wood-as-fuel, or in extreme cases (c) wetlands are drained for wood-as-fuel usage with consequent high loss rates of carbon to the air.

However as shown above, the increased use of wood can lead to increased health effects, unless very clean burning appliances and fuels are used. This is a dilemma, since it leads to contradictory outcomes:

A) Use more wood for heating = displacing gas and thermal electricity generation = lower CO2 emissions. Good for the global environment.


B) Use more wood for heating = increased air pollution emissions = increased health effects on urban populations. Bad for the local environment, and increased health effects.

This is difficult to resolve, and reverts to a policy choice rather than a scientific analysis.

8.2 Achieving the gains

The study conducted here has focused on quantifying the effects of various scenarios for changes in energy use that might occur, because of the growing concern for reducing greenhouse gas emissions, and improving air quality. There has been no significant analysis on how these might be achieved.

For instance it is relatively easy to show the gains from reducing the number of trips taken in vehicles, but achieving this in practice is a whole separate issue. In this case there are a wide range of options, including (a) public education to encourage walking/cycling, (b) improved urban planning to reduce the distances between work-home-leisure activities, (c) tighter vehicle emissions standards, (d) financial instruments such as incentives, or taxes. A number of these measures are being pursued by government agencies such as the Ministry of Transport and Regional Councils (for a more in-depth discussion see the HAPiNZ Study: Fisher et al, 2007).

There are difficulties of a different nature with any fuel switching that involves burning more wood. Apart from the dilemma of the conflicting effects noted above, there are also very strong regional differences and economic factors. The analysis used here has assumed an average national picture, however what occurs in a smaller rural community close to a forest, with cold winters, is very different to what happens in a larger or warmer urban centre. The degree of uptake will depend on fuel prices, wood availability and the rate of installation of new burners (this is covered in much more details in report for the Ministry for the Environment’s Warm Homes project, MfE, 2007).

8.3 Secondary factors

Also not covered to any extent here are a number of secondary factors, and how these might affect the overall emissions and effects.

For instance no attempt has been made to calculate the increased emissions that would result from transporting wood around if its use was to increase. This could offset the CO2 emissions benefits, perhaps by several percent. There is no data available on this subject. This could also increase health costs associated with emissions from the trucks and vans transporting the wood.

Anecdotal evidence also suggests that there may be co-benefits from improving domestic energy efficiency use through insulation and lower costs for more easily obtained fuels (ie, wood). People then keep their homes warmer, and suffer fewer winter health problems. However research on this is New Zealand has only just begun (Wellington School of Medicine and Health Sciences) and suitable data are not available

In addition, no attempt has been made to assess the possible increased emissions associated with producing new biofuels. The overseas studies indicate that these can be substantial.

Likewise, there has been no attempt to analyse the effects of increased forestry plantations that occur for carbon offsetting. These can have co-benefits in some obvious ways, in terms of land use, water quality, aesthetic values, recreation, but they do not generally have any significant or direct benefits in terms of improving air quality.

Finally, no attempt has been made to assess either greenhouse gas emissions or local air pollution effects that might be associated with switching land use to produce biofuels. Internationally, this is being recognised as a growing problem, with the distinct possibility: that in many circumstances using land for biofuel production can result in an increase in the overall greenhouse gas emissions over what it might have been previously.