Geoffrey Heal, Jisung Park. 2013. Feeling the heat: temperature, physiology & the wealth of nations. Working Paper 19725. National Bureau of Economic Research

http://www.nber.org/papers/w19725

ABSTRACT:Does temperature affect economic performance? Has temperature always affected social welfare through its impact on physical and cognitive function? While many studies have explored the indirect links between climate and welfare (e.g. agricultural yield, violent conflict, or sea-level rise), few address the possibility of direct impacts operating through human physiology. This paper presents a model of labor supply under thermal stress, building on a longstanding physiological literature linking thermal stress to health and task performance. A key prediction is that effective labor supply – defined as a composite of labor hours, task performance, and effort – is decreasing in temperature deviations from the biological optimum. We use country-level panel data on population-weighted average temperature and income (1950-2005), to illustrate the potential magnitude of the effect. Using a fixed effects estimation strategy, we find that hotter-than-average years are associated with lower output per capita for already hot countries and higher output per capita for cold countries: approximately 3%-4% in both directions. We then use household data on air conditioning and heating expenditures from the US to provide further evidence in support of a physiologically based causal mechanism. This more direct causal link between climate and social welfare has important implications for both the economics of climate change and comparative development.

摘要：温度影响经济表现吗？温度总是通过它对身体和认知功能的影响来影响社会福利吗？虽然许多研究已经探讨了气候和福利之间的间接联系(如农业产出、暴力冲突、或海平面上升)，但却几乎没有人探讨气候通过人体生理直接影响福利的可能性。本论文以长期存在的热应力与健康及工作表现之间的生理学联系为基础，建立了一个热应力条件下的劳动力供给模型。一个关键的预测在于有效的劳动力供给——工作时间、工作表现及努力程度的复合物——正随着温度对生物学最佳水平的偏离而减少。我们使用国家层面的加权人口平均温度和收入(1950 - 2005)的面板数据来说明这一效应的潜在大小。运用固定效应估计法，我们发现对于已经很热的国家来说，温度较高年份的人均产出较低；而对于那些还很冷的国家来说，温度较高年份的人均产出却较高：两个方向上大约都变化3%—4%，接下来我们使用来自美国的空调和取暖开支的家庭数据进一步得到支持这一因果关系的证据。气候和社会福利之间的这一更直接的因果关系对于气候变化经济学和比较发展有着重要的意义。

数据来源：country-level panel data on population-weighted average temperature and income (1950-2005)；

household data on air conditioning and heating expenditures from the US

研究方法：建立劳动力供给模型；使用面板数据进行计量分析

Conclusion:Three main conclusions emerge from our analysis.

Firstly, there is a clear and significant relationship between temperature and human performance of a range of economically significant tasks. An extensive physiological literature attests to this point, with recent economic studies consistent with these findings.

Secondly, cross-country panel data suggests a single-peaked and significant relationship between output per capita and temperature. While we are far from being able to quantify the exact magnitude of the causal impact of temperature on income, our results suggest that the physiological impact of thermal stress on labor productivity likely plays a causal role. The magnitude of these temperature impacts is large, and suggest that many simulation-based estimates of the costs of climate change may be downward-biased. These results also suggest that integrated assessment models should include the direct effect of climate change on labor productivity, among other direct impacts of thermal stress on the human organism.

Finally, people are willing to pay significant sums for thermoregulation. Furthermore, willingness to pay for thermoregulation varies with basal metabolic rate in the direction that our theory would suggest: younger individuals have a higher willingness to pay for cooling and a lower willingness to pay for heating than older individuals, suggesting that physiological factors significantly influence economic behavior. Using one’s home for income generation increases the willingness to pay for thermoregulation (controlling for income, climate, and electricity prices), consistent with the idea that people want to avoid the impact of heat stress on their productivity.

The bottom line appears to be that temperature affects economic performance at the micro and macro levels enough to be a significant explanatory variable in cross-country comparisons. This suggests a novel and under-emphasized mechanism through which climate change may affect economic activity.

结论：我们的分析得出三个主要结论。

首先，温度和人类在具有重要经济意义的一系列工作上的表现之间具有明显而重大的关系。大量的生理学文献证明了这一点，近期的经济学研究也得出一致结果。

其次，跨国面板数据表明人均产出和温度之间存在单峰值的、重要的关系。尽管目前还不能准确量化温度对收入的影响程度，但我们的研究结果却说明生理热应力对劳动生产率的影响可能是因果关系。这些温度的影响是巨大的，而且表明许多对气候变化成本的仿真估计可能偏低。此外，结果还表明，综合评估模型除了包括热应力对人类有机体的其他直接影响外，还应包括气候变化对劳动生产率的直接影响。

最后，人们愿意支付很多以对温度进行调节，而且支付意愿随着基础代谢率变化，变化方向正是我们的理论所表明的：相对于老年人而言，年轻人对降温的支付意愿更高而对升温的支付意愿则较低，这说明生理因素的确可以显著影响经济行为。对于工薪阶层来说使用房子提高了温度调节的支付意愿（控制收入、气候和电价），这与人们想避免热应力对他们生产力的影响是一致的。

本质其实就是说温度对微观和宏观层面经济表现的影响使其足以成为跨国比较中的一个重要解释变量，这表明了一个新奇且重要的机制，而气候变化可能正是通过此机制影响经济活动的。

（By 杨帆）