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GTAP Resource #4207

"Looking back to move forward: Evaluating global agricultural land use in integrated assessment models"
by Hertel, Thomas and Uris Lantz Baldos

Recently Integrated Assessment Models (IAMs) have incorporated land-based mitigation policies into their analyses as projections of agricultural land use are essential inputs to climate change studies. However, the value of such projections hinges on the scientific credibility of the underlying models. And this depends on model validation – an area in which IAMs have been notably lacking to date.

We illustrate the opportunity and the challenge of undertaking such a validation exercise using the SIMPLE model of global crop sector. We test the model’s performance against the historical period: 1961-2006. Using this 45-year period as our laboratory, we then explore how various model restrictions which appear in the IAM literature alter the model’s historical performance. From our results, we see that SIMPLE slightly overstates the global change in crop production over the 1961-2006 period (206% vs. 196%). The model also slightly understates the historical decline in crop price (24% vs. 29%). SIMPLE does a very good job in predicting the partitioning of supply growth between the intensive and extensive margins, with changes in global cropland and global average crop yield (17% and 162%, respectively) slightly above the observed values (16% and 156%, respectively). However, results at the regional level are less favorable, highlighting the challenge of predicting the distribution of cropland expansion across the globe.

After validating the model, we turn to an investigation of how the specific assumptions imbedded in many IAMs influence the results of this historical exercise. We find that those models which are largely biophysical – ignoring the price responsiveness of demand and supply likely understate changes in crop production, while overstating price changes. Many of the models which do incorporate economic responses do so based on annual time series estimates which likely understate long run responses to price changes.

Resource Details (Export Citation) GTAP Keywords
Category: 2013 Conference Paper
Status: Published
By/In: Presented at the 16th Annual Conference on Global Economic Analysis, Shanghai, China
Date: 2013
Created: Baldos, U. (4/15/2013)
Updated: Baldos, U. (4/15/2013)
Visits: 2,056
- Model validation and sensitivity analysis
- Land use

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