The yellow line indicates the median minimum level of arctic ice from 1979-2000–yesterday’s record low area of ice should scare a sea-level New York City already anticipating flooded subways and airports when storms hit in future decades. The minimum area of arctic sea water covered by ice fell below the record held in 2007–a record enabled by pressure patterns that produced warm winds off several arctic coasts. These patterns repeated this year, but were much less intense, yet sea ice melt rates reached 57,900 square miles per day in 2012, nearly twice the long-term rate.

The loss of so much sea ice means that when ice reforms over the winter, it is “first-year ice,” which is much thinner than sea ice that has persisted over multiple years. Joey Comiso, senior research scientist at NASA Goddard Space Flight Center, explained that the loss of this multiyear ice contributed to record low ice extent in 2012.

Once sea ice loss gets underway, it can become a self-reinforcing process. Because there is less light-colored ice to reflect the Sun’s energy back into space, more energy is absorbed by darker ocean water.

Though NASA’s Goddard Space Flight Center and National Snow and Ice Data Center (NSIDC) differed whether a strong summer cyclone seriously contributed to the record low. The record low does fit into the larger pattern of a changing arctic; but as NSIDC director Mark Serreze says, “What is perhaps most surprising [about the loss of ice] is that we are no longer surprised.”

(Photo: Jesse Allen/NASA Earth Observatory)