The pace of Arctic warming is about double that at lower latitudes—a robust phenomenon known as Arctic amplification. Many diverse climate processes and feedbacks cause Arctic amplification, including positive feedbacks associated with diminished sea ice. However, the precise contribution of sea-ice loss to Arctic amplification remains uncertain. Through analyses of both observations and model simulations, we show that the contribution of sea-ice loss to wintertime Arctic amplification seems to be dependent on the phase of the Pacific Decadal Oscillation (PDO).

Changes in climate variability are arguably more important for society and ecosystems than changes in mean climate, especially if they translate into altered extremes. There is a common perception and growing concern that human-induced climate change will lead to more volatile and extreme weather4. Certain types of extreme weather have increased in frequency and/or severity, in part because of a shift in mean climate but also because of changing variability.

Climate change does not occur uniformly around the world: instead, in a process called polar amplification, the Arctic warms more rapidly than the tropics or mid-latitudes. Recent work published in Nature suggested that upper-atmospheric transport processes accounted for much of the recent polar amplification, but this conclusion proved controversial.