In many countries, GDP varies by several percent from quarter to quarter. It has long been conjectured that temperature plays a role in these cycles, but previous research has either neglected its possible influence, focused on proximate rather than fundamental drivers of quarterly fluctuations, or concluded that the influence of temperature is small based on limited evidence and inappropriate methods. As climate change is projected to change the seasonality of temperature, the question appears very relevant. In this paper, I examine the effect of seasonal temperature variability on seasonal economic cycles using data on quarterly GDP from 98 countries and quarterly GVA by industry for 35 European economies. I first construct a dataset of s...