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

This paper quantifies 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 alongside 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 8–11%, 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, independent of war or policy, can reshape the global geography of scientific talent and knowledge.