We investigated the effects of climato-economic harshness on extreme response style. Climato-economic theorising postulates that a more threatening climate in poorer countries, in contrast to countries with a more comforting climate and richer countries with a more challenging climate, triggers intolerance of ambiguity and uncertainty avoidance inherent to conservatism, in-group favouritism and autocracy. Scores of extreme response style at country level, a proxy of this cluster of cultural characteristics, were extracted from students' responses in the Programme for International Student Assessment to test the hypothesis. In a series of hierarchical regression analysis across 64 countries, cold demands, heat demands and GDP per capita showed a highly significant interaction effect on extreme response style, predicting in total 30.7% of the variance. Extreme response style was highest in poorer countries with higher climatic demands, and lowest in richer countries with lower climate demands. Implications are discussed.