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9 Conclusion

It is possible with existing data to make quantitative estimates in both physical and monetary terms, of the health co-benefits and co-costs (via changes in air quality) associated with measures to reduce emissions of greenhouse gases. They are indicative only, because such estimates do not cover all aspects of air quality, are sensitive to a number of the assumptions made (eg, GHG emission factor for electricity; level of PM10 emissions from an expanded population of wood burners) and because a high degree of subjectivity attaches to the monetary estimates.

An analysis has been made of the potential co-benefits between measures to reduce greenhouse gas emissions and measure to improve public health through reducing air pollution.

This has been conducted using the data available on air pollution health effects from the HAPiNZ Study (Health and Air Pollution in New Zealand) and from the national greenhouse gas inventory (New Zealand’s Greenhouse Gas Inventory 1990–2005).

The focus has been on those emissions which have significant effects in both these areas, and thus are more significant for potential co-benefits, or costs. These are essentially activities and processes that involve combustion of fossil fuels – domestic heating using wood burners, transport, thermal electricity generation, and energy use in industry. The analysis has been based mainly on CO2, since processes generating other greenhouse gases have little if any health effects. Some smaller changes in methane emissions are also included. The main contaminant associated with health effects is particulates (as PM10), with associated emissions of carbon monoxide and oxides of nitrogen.

A number of plausible scenarios have been examined involving changes in the key sectors that result in either a reduction in air pollution emission, a reduction in greenhouse gas emissions, or both – domestic heating, transport, and industry.

The scenarios examined show that co-benefits are possible, but so are contrary outcomes. The best gains are obtained in the transport sector, with either (a) reducing the amount of general vehicle use, or (b) increasing biofuel use. Whilst having people use wood burners more – with a carbon neutral fuel – can have gains for reducing greenhouse gas emissions, these are almost certainly offset by the larger cost rises in public health effects, even with new low emissions burners. Improving energy efficiency across the industrial sector also has modest gains and co-benefits for both greenhouse gases and air quality.

The largest individual benefit identified ($180M net) was having 25% of wood burner users convert to electricity (heat pumps), but this did not create a significant co-benefit as the increased thermal electricity generation required produced an additional greenhouse gas cost ($3M).

Clear and consistent co-benefits occur with almost any measure to reduce the use of fossil fuels in transport. Even modest 10% reductions in travel demand resulted in significant net co-benefits ($81M net).

The largest co-benefit identified was the introduction of 20% of biodiesel into the transport sector ($18M in greenhouse and $99M in health effects, giving $117M net). However this result needs to be interpreted with caution, as the research on air quality benefits from biodiesel are not confirmed, and further research on New Zealand specific features is needed.

Different values for factors such as the GHG emission factor for electricity or the level of PM10 emissions from an expanded population of wood burners, and different values for the cost of GHG emissions or the cost of health effects would change the relative benefits and costs, and the total net benefits, of the scenarios examined.