The latitude gradient in comparative development is a striking fact: as one moves away from the equator, economic activity rises. While this regularity is well known, it is not well understood. In the present paper we take a step towards unpacking this gradient. Perhaps the strongest correlate with (absolute) latitude is the intensity of ultraviolet radiation (UV-R), which epidemiological research has shown to be a cause of a wide range of diseases. We establish that UV-R is strongly and negatively correlated with economic activity, both across and within countries. We propose, and test, a mechanism that links UV-R to current income differences via the impact of disease ecology on the timing of the take-off to sustained growth.

Empirically, a higher frequency of lightning strikes is associated with slower growth in labor productivity across the 48 contiguous U.S. states after 1990; before 1990, there is no correlation between growth and lightning. Other climate variables (e.g., temperature, rainfall, and tornadoes) do not conform to this pattern. A viable explanation is that lightning influences IT diffusion. By causing voltage spikes and dips, a higher frequency of ground strikes leads to damaged digital equipment and thus higher IT user costs. Accordingly, the flash density (strikes per square kilometer per year) should adversely affect the speed of IT diffusion. We find that lightning indeed seems to have slowed IT diffusion, conditional on standard controls. Hence, an increasing macroeconomic sensitivity to lightning may be due to the increasing importance of digital technologies for the growth process.