https://doi.org/10.1029/2025JD045714

Basnet, S., & Thériault, J. M. (2026). Near-0°C temperature pathways from high-resolution simulation in current and pseudo-global warming future over eastern Canada and United States. Journal of Geophysical Research: Atmospheres, 131, e2025JD045714. https://doi.org/10.1029/2025JD045714

Near-0°C (−2°C to +2°C) air temperatures are critical for determining the phase of precipitation, the onset of freeze–thaw cycles, and associated impacts on the environment and infrastructure. Change is expected in a warming climate, yet large-scale high-resolution understanding of near-0°C transitions remains limited, particularly under future conditions. Here, we used 11-year high-resolution (2.5-km) regional climate simulations for current and future warmer scenarios to assess near-0°C temperature pathways across eastern Canada and the United States. We showed that the annual 0°C isotherm shifts northward in a warmer climate, with near-0°C hours increasing in northern regions and decreasing in the south. We studied how temperatures move in and out of the near-0°C range and found that events staying entirely above 0°C (P3) are more common in southern areas, whereas those staying entirely below 0°C (P4) are more frequent in the north. In the warmer climate, the dividing line between these two patterns shifts farther north. Except for P4, most pathways that occur in the spring in the current climate occur in the winter in warmer climates, especially in the northern part of the domain. In warmer climate conditions, temperature distributions in northern regions show a more pronounced peak near 0°C, whereas in southern regions, the peak near 0°C occurs less often. These findings demonstrate that near-0°C pathways and peaks will undergo spatial and temporal reorganization in warmer climate conditions.

Temperatures near 0°C are considered important because they are linked to risks for roads, infrastructure, and flooding. In this study, model simulations were used to examine how near-0°C temperatures occur across eastern Canada and northeastern U.S., and how they are expected to change under a warmer climate conditions. In a warmer climate, it was found that the areas experiencing the most near-0°C conditions shift northward, with a decrease observed in southern areas and an increase in the north. The ways in which temperatures pass through 0°C were also analyzed. Two common patterns were identified: one in which temperatures cool and then warm, and another where they warm and then cool. These patterns were found to occur more frequently in the south and north, respectively. It is suggested that these transitions are influenced by precipitation, snow cover, and radiation heating. In the southeastern U.S., fewer occurrences of near-0°C temperatures compared to neighboring temperature ranges are suggested to occur in warmer climate conditions.

https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2025JD045714