Arctic sea ice extent dropped to the lowest level ever recorded, bottoming out at 3.41 million square kilometers on September 16, according to the National Snow and Ice Data Center (NSIDC). That’s 49 percent below the average minimum recorded during the 1980s and 1990s.
Scientists are confident that this trend is due to pollution. While there are year-to-year fluctuations in the location and extent of arctic sea ice, driven primarily by wind patterns, the best estimates are that the minimum extent never dropped below 9.8 million square kilometers in the first half of the 20th Century and probably not below 9 million in the last 1000 years. Since around 1950 there has been a clear trend toward less ice, with the minimum extent dropping below 4 million square kilometers for the first time this year.
Wind-driven reorganization of the sea ice also can’t explain the progressive reduction of ice thickness and the declining fraction of ice that has persisted for more than one year. These trends not only bear the fingerprint of human-caused climate change, they mean that the arctic ice is ever more vulnerable to collapse. In fact, arctic sea ice is meltingmuch faster than climate models had predicted.
Unfortunately, what happens in the arctic doesn’t stay in the arctic. The dramatic loss of arctic ice contributes to more extreme weather in the United States in at least three ways.
First, the dramatic reduction in reflective ice in the Arctic Ocean changes the flow of energy in the climate system throughout the northern hemisphere. In particular, it alters the position and shape of the jet stream, favoring a pattern with more pronounced waves. That means that tropical air can penetrate further north and that arctic air can penetrate further south. It also means that weather systems tend to move more slowly from west to east. This is a formula for increasing extreme weather—both persistent excessive heat and severe snow storms.
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