What Factors Contribute to Recent Rapid Wintertime Arctic Warming?
The Arctic is very sensitive to climate change and is currently experiencing much faster warming than the global trend. A research team analyzed observational data sets and identified a 1.1 degree per decade Arctic surface warming trend during winters between 1979 and 2020 (October–February). This is five times higher than the global mean. Based on surface energy budget analysis, researchers attribute the largest fraction (∼82%) of this cold season warming trend to an increase in downward infrared heat under clear-sky conditions. They found that the downward infrared heat in the Arctic is sensitive to recent changes in the strength of the temperature inversion, a layer of warm air above the surface.
Researchers analyzed the Arctic energy budget based on high-resolution observation-based datasets to identify the important role of the downward infrared energy flux in driving the cold season Arctic surface warming. They also found a close connection between summer sea ice concentrations and Arctic warming the following cold season (the ocean heat gained in summers with low sea ice concentrations can be released into the atmosphere in the winter). The observed connections between sea ice amount and seasonal Arctic temperature may be missed in many climate models. These relationships can be applied to evaluate models and narrow the uncertainty in their projections of Arctic changes.
Observational data and climate models have consistently shown a stronger surface warming in the Arctic than the global mean. This is known as Arctic amplification (AA) and is stronger in the winter than in the summer. Previous studies have suggested two key feedbacks important to AA: the surface-albedo feedback, which refers to an increase in sunlight absorbed at high latitudes when sea ice decreases, and the lapse-rate feedback, which refers to the change in energy emitted to space as the temperature profile changes. Details of which feedback dominates and why remain unclear. This study identified a unique role for the lapse-rate feedback associated with changes in temperature and water vapor near the surface in the presence of wintertime inversions. This feedback operates very differently in the tropics and Arctic summer. The researchers further linked the changes in cold season inversion to the sea ice loss occurring during the preceding warm season. These results used observations from winters between 1979-2020 to reinforce and quantify the previous findings that lapse-rate feedback and sea ice loss play a key role in AA. They also show that the lapse-rate feedback in the cold season is likely a consequence of sea-ice albedo feedback from the preceding warm season.
This research used National Energy Research Scientific Computing Center, a Department of Energy Office of Science User Facility, resources.