The vast Arctic ice sheet shrinks somewhat as the seasons shrink. Near the edge, there is an ultra-thick ice layer that will persist and will not melt even in summer. We call this ice sea ice for many years (pink below). However, because the average temperature of the earth has been rising, scientists have found that in the past 40 years, the sea ice for many years has been unable to persist, and it has melted from about 7 million square kilometers, leaving only 4 million square kilometers of sea ice. When will the sea ice melt completely in these years? That is to say, by then, the phenomenon that the Arctic will be ice-free in summer will be named' blue ocean event'.
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