The UK summer heatwave of 2018 led to changes in consumer behaviour, including large increases in electricity demand due to increased use and intensity of refrigeration and air-condition devices (1, 2). While the UK experienced its equal hottest summer on record, the extreme temperatures were concentrated in the south and east of England (3). We exploit the regional variation to test for the effect of experiencing extreme temperatures on resource security perceptions and related pro-environmental behaviour. We analyse data from 2,189 individuals across the UK over a seven-day period and employ a difference-in-differences type estimation to compare individuals’ responses in regions subjected to extreme temperatures with individuals’ responses in regions that were not subjected to extreme temperatures (4). We show evidence that suggests exposure to extreme temperatures had a large and statistically significant effect on perceptions of energy security but not on stated pro-environmental behaviour. We find less evidence that extreme temperatures had an effect on perceptions of food and water security.