Too hot to play it cool? Temperature and negative media bias

Abstract This paper examines the impact of outdoor temperature on media bias in a quasi-experimental setting. We take advantage of the geographical proximity of the locations of the three major US news networks, ABC News, CBS News, and NBC News, all headquartered in New York City, and granular variations in local daily temperatures. We use more than 10 years of daily hand-coded data on the tonality of evening weekday news broadcasts by each news network to estimate the effect of hot weather on negative media bias in reporting the news affiliated with the Republican and Democratic parties, controlling for time and network-month fixed effects. In line with theoretical expectations regarding human behavior, our results suggest an increase in negative media bias: a 0.5 °C (0.9 °F) increment in daily maximum temperature on a hot day (> 25 °C or > 77 °F) leads to about a 10% increase in the negative bias measured as the difference in the share of negative news about the Republicans and the Democrats. This effect is mainly driven by an increase of the share of negative news about the Republicans. This bias in political reporting exists only for maximum temperatures, as opposed to minimum or average temperatures. The results are robust to an array of placebo tests using past or future temperatures. Examining a similar effect for positive coverage bias, we detect precisely null effects, suggesting that high temperatures are associated only with biased negativity in reporting.