Climate change impact studies inform policymakers on the estimated damages of future climate change on economic, health and other outcomes. In most studies, an annual outcome variable is observed, e.g. agricultural yield, annual mortality or gross domestic product, along with a higher-frequency regressor, e.g. daily temperature. While applied researchers tend to consider multiple models to characterize the relationship between the outcome and the high-frequency regressor, a choice between the damage functions implied by the different models has to be made to inform policy. This paper formalizes the model selection problem and the policy objective in this empirical setting in light of current empirical practice. We then show that existing model selection criteria are only suitable for the policy objective under specific conditions. These conditions include a requirement that one of the models under consideration nests the true model. To overcome this restriction, we propose a new criterion, the proximity-weighted mean-squared error (PWMSE) of predicting climate change impacts. The PWMSE targets the policy objective of predicting the impact of projected climate change directly by giving higher weight to prior years with weather closer to the projected scenario. We show that our approach selects the best approximate regression model that has the smallest weighted error of predicted impacts for a future climate scenario. A simulation study and an application revisiting the impact of climate change on agricultural production illustrate the empirical relevance of our theoretical analysis.
翻译:气候变化影响研究使决策者了解未来气候变化对经济、健康和其他结果的估计损害。在大多数研究中,观察到年度结果变量,如农业产量、年死亡率或国内生产总值,以及高频回升器,如每日温度。虽然应用的研究人员倾向于考虑多种模型来描述结果与高频回退器之间的关系,但必须在不同模型所隐含的损害功能之间作出选择,以便为政策提供依据。本文件根据目前的实证做法,将模型选择问题和这一经验环境中的政策目标正式化。然后我们表明,现有的模型选择标准只适合特定条件下的政策目标。这些条件包括要求考虑中的模型之一嵌套真正的模型。为了克服这一限制,我们提出了一个新的标准,即预测气候变化影响的近比平均差差差差差差差。PWMSE的目标是,通过将预测气候变化的影响直接预测的政策目标确定为政策目标,在与预测的假设情景相近的前几年给予更高的份量。我们提出的现有模式选择标准选择了仅适合特定条件下的政策目标。这些条件包括要求所考虑的模型将真正的模型嵌套在真正的模型中。为了克服这一限制,我们提出的未来对气候变化影响进行最精确的模型的模拟分析。我们要选择了对气候变化影响进行最精确的预测的模型。