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Climate change and agricultural production

Dealing with a Range of Possible Futures

How can the future be modelled when there is uncertainty in the behaviour of weather and biological systems, agricultural production, and economic outlooks? These areas are complex by themselves, and together the task becomes even more complicated.

The global rate of climate change depends on the levels of greenhouse gases emitted into the atmosphere. In turn, the amount of gases emitted depends on political decisions, as well as economic and social factors. Scenarios are used to consider a range of emission levels based on different economic and social assumptions. Models are then run using the scenarios to estimate the global temperature changes.

For this initial study the consortium drew on the scenarios used by the Intergovernmental Panel on Climate Change (IPCC) in the third and fourth assessment reports published in 2001 and 2007. To estimate the effects of climate change on future production, the EcoClimate report used downscaled climate change projections to estimate changes in the annual growing degree day values and changes in the soil moisture deficit.

The EcoClimate report uses the UK Hadley Centre model from the IPCC third assessment report and focuses on local changes corresponding to medium-low and medium-high emission scenarios. This enabled the consortium to examine how New Zealand pastoral production might change for the central 50% of the IPCC temperature projections.

For example, the global model over a certain period might indicate a temperature increase from 1 to 5 degrees centigrade (a range of 4 degrees). The basis for modelling is provided by using 25 and 75 percent of this range (2 to 4 degrees centigrade). These outcomes are referred to in the EcoClimate report as h25 and h75.

The report considers two main future 30-year periods from the third assessment report: 2020–2049, and 2070–2099. These periods are referred to by the central values, that is, as the "2030s" and "2080s", respectively. The report then analyses the differences between projections for these periods with values calculated in the 1972-2002 period. The results of these studies are presented for the entire country and by regions using the h25 (medium-low) and h75 (medium-high) values for both future periods.

Contact for Enquiries

Sustainable Land Management and Climate Change
MAF
Pastoral House
25 The Terrace
PO Box 2526, Wellington
Tel: 0800 CLIMATE (254 628)
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