Male labor force participation rates (LFPR) in developed economies have been declining since the 1970s. This paper argues that modern climate change has fueled dropouts of adult males by eroding the traditional advantage of working outdoors. Using exposure to climate change across US commuting zones constructed from granular daily weather records for nearly half a century, I find that extreme temperature days hurt the LFPR of prime-age males. In the new century, climate change accounts for approximately 10-15 percent of the nationwide decline in LFPR. I find that out- door jobs—prevalent across sectors and prominent in disadvantaged regions—are likely hotbeds of dropout. Disability accounts for a substantial proportion of climate-induced dropouts, but the majority of these are likely due to preference; the decline in LFPR has been catalyzed by the spread of housing amenities (e.g., air conditioning and cable TV) and access to affluent family backgrounds. Overall, the results suggest that climate change exacerbates socioeconomic inequality.The paper has been presented at seminars at GRIPS, Hitotsubashi, Keio, Kyoto (empirical), Kyoto (urban), Tokyo Labor Economics Workshop, Waseda, the 2024 Trans-Pacific Labor Seminar at the University of California, Santa Barbara, the 2024 Japanese Economic Association Fall Meeting, and the 2024 Econometric Society Australasia Meeting. The paper is currently under review.

　米国では金融不況以後、労災率が下げ止まっている。産業用ロボット導入が加速的に進む中、なぜ労災率が下がらないのだろうか。一方で労災率が高い農業や建設では、南米からの移民が半数近くを占めている。この研究は移民流入とロボット化が労災率に与える影響を、操作変数法を用いて、実証的に分析した。  国勢調査の雇用データと、労働統計局(Bureau of Labor Statistics)の労災記録を産業別に組み合わせ、1992-2019年のパネルデータを構築したところ、移民の依存率が高まると、ネイティブ労働者の労災数（死亡・傷害を含む）を減らすことを発見した。　さらに国際ロボット連盟(International Federation of Robotics)の産業別のロボットの投資データを組み合わせ、特に製造業におけるロボット導入が著しく労災率を下げたことがわかった。すなわち、国レベルでの労災率が下がらないのは、農業や建設業など自動化が進まない、労働集約的で危険な産業の雇用ウェイトの寄与度が大きい。　これらの結果を踏まえ、低技能移民の流入で労働供給が増えると、労働代替的なロボット技術への投資が鈍るという技術変化の仮説を立て、実証的に有意な結果を得た。すなわち、移民の流入はネイティブの労災自体を減らすが、危険な労働環境を温存させ、同環境で働き続けるネイティブの労災率を底上げするようである。　背景として、少子化で労働力不足が進む中、雇用者の移民労働力への依存が起きやすい構造にある。移民には不法入国者が多数おり、最低賃金の遵守や、無保険で労災の保険負担が発生しにくい。統計である労災の背後には、労災認定されない慢性的な肉体負担（関節や筋肉への痛み）があると考えられる。米国の州のパネルデータで傷害率と、鎮痛剤のオピオイド死亡率の強い正の相関を発見した。進行する移民依存が労災の下げ止まりを通じて、全米最悪と言われるオピオイド薬禍の温床となった可能性が示唆される。　これらの研究結果を論文にまとめ、春季日経学会（2024年5月開催）で採択され、発表予定である。

   In 1900, a workplace injury was a 6 time higher mortality of the U.S. citizens compared to suicides. Throughout the century, a workplace injury rate has been constantly declining from mechanization of operations. After the Great Recession, however, improvement of the injury risk has almost stalled at a still alarming level despite the acceleration of automation. Why has the injury risk been stagnant?   Associating investment of robots and workplace injuries across primary and manufacturing sectors during 1992-2019, I find that installation of industrial robots dramatically reduced injury risk. A decomposition exercise shows that the aggregate risk remains high from sluggish investments to inherently higher-hazard sectors (e.g. agriculture; mining; construction).   In these sectors, by contrast, I document that foreign labor represents a growing fraction of manual-intensive occupations that appear to be close substitutes of industrial robots. I find that immigrant workers substantially replace native injuries by crowding out natives out of risky jobs. Then, I show that immigration inflow impedes the adoption of automation and preserves an injury risk for remaining native laborers. Over-dependency on foreign labor may preserve the risky technology generating a social cost including expanding disability insurance benefits.