Is Marlborough carbon neutral? Investigating the greenhouse gas budget of the Marlborough Region, New Zealand

Abstract

Under the Kyoto Protocol, New Zealand is responsible for estimating and reporting its national greenhouse gas (GHG) emissions and, by the first commitment period (2008-2012), reducing its total national emissions to those of 1990. So far New Zealand's gross emissions are 21.6% above its target and it is questionable whether its stated goals will be achieved. To reduce GHG emissions it is necessary to identify and quantify specific emission sources and the New Zealand Government is encouraging regional authorities and private industries to take a role in this.

The objectives of this study were to identify and estimate all significant GHG sources and sinks for the Marlborough Region, to create an in-depth view on actual emission sources and sinks, and to provide a basis for the development and implementation of regional reduction measures and policies. Marlborough's regional activities were classified according to the six sectors outlined by the Intergovernmental Panel on Climate Change (IPCC): Energy; Agriculture; Industry; Waste; Land-Use Change and Forestry; and Solvents and other Products. Each sector was subdivided into single emission sources. The emissions were estimated using available regional data, by applying both bottom-up and middle-up approaches. The emission estimates were also based on IPCC guidelines and New Zealand specific models. The agricultural sector is the largest emitter in Marlborough, emitting 468 Gg of CO₂equivalent GHGs per year in 2003, representing about 55% of the total regional emissions. The energy sector emits a further 340 Gg CO₂ equivalent, representing 40% of the total regional emissions. The waste sector emits the remaining 5% (41 Gg CO₂ equivalent).

The largest single emission source is enteric fermentation, from animals emitting 309 Gg CO₂ equivalent, which equals about 66% of the agricultural emissions and 36% of the total regional emissions. Transport-related emissions add up to 305 Gg CO₂ equivalent, are about 90% of the energy-related emissions and 36% of the total regional emissions. No emissions from the industry sector could be identified, because all major GHG-producing industries in Marlborough were already accounted for under the Agriculture or Energy sector. Solvents and other products have been omitted due to their insignificance in New Zealand and for Marlborough in particular. The amount of carbon sequestered could only be estimated for the exotic forest plantations, which have been estimated to take up 937 Gg CO₂ per year. However, due to forest harvests, which are counted as an emission (397 Gg of CO₂ equivalent), the overall uptake was reduced to 540 Gg CO₂ equivalent. The carbon stored in indigenous forests, to date, could not be calculated satisfactorily as no suitable model for overall regional estimates could be identified. The final emissions budget for Marlborough equals +310 Gg CO₂ equivalent, signifying that Marlborough emitted a net 310 Gg of CO₂ equivalent GHGs in 2003, which is low compared with emission estimates based on national average figures and on the region's population. A reason for Marlborough's low GHG budget is its large area of exotic forest plantations. This, on the other hand, creates a huge liability (carbon debit) for Marlborough when these forests are harvested, making the year-to-year variation in net emissions very sensitive to annual harvesting. The uncertainties of the values calculated are relatively large and may influence the overall emission budget. Nevertheless, the figures calculated and their respective uncertainties represent the current state of knowledge.