The United States “Warming Hole”: An Update to 2016 and Application to Equivalent Temperature

Several recent studies have investigated a period of cooling (or lack of warming) in the eastern United States, which is commonly referred to as a “warming hole”. The lack of warming has been attributed to disparate factors, such as atmospheric aerosols, feedbacks related to surface hydrology, and even large scale modes of climate variability. However, a clear definition of the warming hole (i.e., it’s temporal and spatial extent) has not been presented and potentially limits further exploration of physical drivers. Furthermore, the warming hole has traditionally been defined using air temperature, rather than alternative metrics, such as equivalent temperature, that combine temperature and humidity to better reflect the total heat content of the lower atmosphere. Here, we provide an update on the status of the United States warming hole using high resolution (4 km) monthly PRISM data from 1948-2016. For seven US regions, we consider the areal proportion that is significantly cooling, non-significantly cooling, non-significantly warming, or significantly warming. We find that the warming hole is still present and is best characterized by non-significant cooling. An equivalent temperature warming hole also exists, but is characterized by less spatial coherence and a center over the southwest region associated with drying over the period of record.