Forecasts and Climate Mortality Estimates
Abstract
Temperature-related mortality is estimated to be one of the largest sources of climate change damage. These estimates come from regressing mortality on realized temperature but ignore the presence of weather forecasts. Prior work has shown that forecasts can help people avoid mortality from temperature. In the presence of forecasts, existing temperature-mortality estimates mask heterogeneous effects coming from time periods when temperature it curately versus inaccurately forecasted. This can bias projected mortality responses to climate change in either direction, depending on how forecast quality evolves as the climate changes.The project combines CDC data on mortality at the county-day level with weather observations from PRISM and weather forecasts from the National Weather Service. The forecasts are widely viewed by the public on cell phones, the web, local new stations, and newspapers.
Theoretically, current estimates of the effect of temperature on mortality are averages over the forecast error distribution. To unpack this heterogeneity, we flexibly regress mortality on temperature, temperature forecasts, and the interaction of the two variables.
We find that accurately forecasted weather has much smaller effects on mortality. For example, the hottest 1% of days in the US cause a reduction in mortality compared to a moderate day if the hot day is accurately forecasted. In contrast, if there is a forecast error on a hot day, then mortality increases rapidly. Under the assumption that current forecast quality remains fixed, mortality projections are close to central estimates from recent integrated assessments. If forecast quality continues to improve at historical rates, mortality damages are projected to be 20% lower than current estimates. A large unknown, however, is whether climate change will reduce forecast quality. Current evidence on this effect is mixed, meaning that more research should be done to understand how climate change will influence forecasts.