Sea ice is generally moderated by sunlight—it grows in the winter and melts in the summer—but there are other factors at play in the decline of ice in the Arctic Ocean. Warm ocean currents travel north from the equator and usher in warmer and warmer water, making sea ice growth difficult. Weather patterns over the high mid-latitudes and the Arctic can also affect sea ice growth. Under normal climate conditions, cold air is confined to the Arctic by the polar vortex winds, which circle counter-clockwise around the North Pole. As sea ice coverage decreases, the Arctic warms, high pressure builds, and the polar vortex weakens, sending cold air is spilling southward into the mid-latitudes, bringing record cold and fierce snowstorms. At the same time, warm air will flowing into the Arctic to replace the cold air spilling south, which drives more sea ice loss. This reversal could be partially driven by sea ice loss, and so is expected to surface more often in the coming years.