(CNN) From year to year, the ice around the Arctic ebbs and flows, reaching a minimum and maximum as the temperature shifts through the seasons.

Scientists recently released time-lapse animation comparing Arctic sea ice since 1984 with now, and it is a little startling. The old sea ice -- the Arctic sea ice that lasts year after year -- is smaller than it has been in three decades.

You see, sea ice is kind of like plants. There are seasonal and perennial sea ice. The perennial sea ice lasts from one year to the next and represents the thickest ice. It can last for four, or even up to nine years or more without melting during the warmer summer months and can be at least 4 meters thick.

But lately, the thinner, younger sea ice -- less than a year -- has become the majority across the Arctic. Young ice struggles to reach 2 meters thick during winter months and then is more likely to melt during the summer.

In September, Arctic sea ice shrank to the second-lowest level since records began in 1979. The lowest sea ice extent was recorded on September 17, 2012, when it fell to just 1.31 million square miles (3.39 million square kilometers).

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