Building a Wall Around Science: The Effect of U.S.-China Tensions on International Scientific Research

This paper examines how rising U.S.–China geopolitical tensions reshaped international science along three dimensions: trainee mobility, cross-border knowledge flows, and researcher productivity. Using a difference-in-differences design with detailed CV and publications data, we find ethnically Chinese students became 15% less likely to enter U.S. doctoral programs and 4% less likely to remain in the U.S. after graduation. China-based scientists cite U.S. research less frequently, while U.S. citations of China-produced work remain unchanged on average. Productivity among U.S.-based ethnically Chinese researchers declined by 8–12%, with a 10% higher rate of exit, but we do not see the same declines in China-based researcher productivity. These patterns cannot be explained by formal policy changes alone and instead point to a chilling effect driven by perceived hostility. Our results highlight how geopolitical tensions can reshape the global geography of scientific talent and knowledge even when they operate through perceived hostility rather than outright exclusion.