Future changes in Northern Hemisphere summer weather persistence linked to projected Arctic warming.

Understanding the response of the large-scale atmospheric circulation to climatic change remains a key challenge. Specifically, changes in the equator-to-pole temperature difference have been suggested to affect the mid-latitudes, potentially leading to more persistent extreme weather, but a scientific consensus has not been established so far. Here we quantify summer weather persistence by applying a tracking algorithm to lower tropospheric vorticity and temperature fields to analyze changes in their propagation speeds. We find significant links between slower propagating weather systems and a weaker equator-to-pole temperature difference in observations and models. By end of the century, the propagation of temperature anomalies over mid-latitude land is projected to decrease by -3%, regionally strongest in southern North America (-45%) under a high emission scenario (CMIP5 RCP8.5). Even higher decreases are found (-10%, -58%) in models which project a decreasing equator-to-pole temperature difference. Our findings provide evidence that hot summer weather might become longer-lasting, bearing the risk of more persistent heat extremes.