The annual volume of sea ice in the Arctic peaks every year around the end of April, but this year the peak will be 8% to 10% below the previous record low, based on the stunning record low volume at the end of March, 2017. The cause of the drop is both obvious and complicated. The obvious cause is the record warm weather of the past two cold seasons in the Arctic. The changes in the weather patterns causing this record warmth are complicated. Simply stated, ocean storms have carried record amounts of heat from both the Pacific and Atlantic oceans into the Arctic. Storm tracks the past two winters have repeatedly blown warm humid air northwards from the oceans to the Arctic. A feed back between record low sea ice amounts and warm storms may have developed over the past decade because open water supports the intensification and northward movement of storms. Research studies have found that huge bubbles of warm air called blocking highs are more likely to develop as sea ice retreats in the seas on the Atlantic side of the Arctic. The blocking highs weaken the polar vortex, allowing cold air to escape from Siberia and warm air to enter the Arctic from over the Atlantic ocean. This winter the blocking patterns were exceptionally strong on both the Atlantic and Pacific sides of the Arctic, bring record warmth to the region from 80º N to the north pole.
The sea ice volume for the end of March has been in rapid decline over the past 30 years as the Arctic has warmed much faster than temperate and tropical regions. This drop in sea ice volume is one of the most obvious and stunning effects of climate change caused by human activities.
Warming summers over the past decade have brought on higher levels of volume melt from May through September. Most melt seasons over the past decade have exceeded 18,000 cubic kilometers of ice loss. Unless this summer is colder and stormier than average for the past decade, we will likely see a record low volume level come this September. However, NOAA’s CFSv2 model predicts a sunny and warm May and June, which would bring on a strong melt season this summer.
The forecast for a warm Arctic spring and early summer seems likely to verify because El Niño is developing, bringing warm temperatures to the north Pacific ocean and added heat to the atmosphere.
Hat tip to Neven’s sea ice blog and sea ice forum.