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Arctic Sea Ice by the Decade

Audio Commentary

Melting Arctic sea ice concerns scientists not just because it verifies the projections of climate models, adding to the evidence for climate change, but because it exposes dark ocean, which absorbs even more energy from the sun, warming the planet further.  This animation begins in 1979, less than a year after regular satellite observations began, and, as the hand of the clock sweeps around, redraws the minimum September ice extent each decade later. For comparison, the outline of 1979’s ice remains, in red. It’s clear that the total area covered by ice has gotten progressively smaller over time.

The Arctic has long been of special concern to climate scientists because of its unique geography: it’s mostly ocean, and mostly covered with ice. The ice melts partly back in summer, exposing open water, then refreezes in the dark and frigid winter.

As the Earth warms overall due to increased levels of atmospheric greenhouse gases, the summer melt is projected to be more widespread—and DoD and NASA satellite observations show that this is precisely what has been happening. This graphic, based on direct observations by satellites orbiting from pole to pole, shows how much of the Arctic Ocean is covered by ice at the September minimum. That’s the day, at the end of summer, when the ice has finished the season’s melting and begins refreezing again. For reference, ice-covered Greenland is at the bottom of the “clock”; North America is to the lower left, Europe on the lower right, and Russia on the upper right.

The audio clip on this page excerpts an interview with Claire Parkinson, a climatologist at NASA’s Goddard Space Flight Center in Maryland and the Aqua satellite project scientist. The data underlying the graphic came from instruments on several DoD and NASA satellites, including:

Nimbus 7: Launched in October 1978, Nimbus carried an instrument called the Scanning Multichannel Microwave Radiometer, abbreviated SMMR, which operated until August of 1987. It worked by detecting the microwave radiation emanating from the Earth’s surface. Microwaves are a form of invisible light naturally emitted by all kinds of objects; open water, ice and land radiate a different mix of microwave wavelengths, allowing scientists to tell exactly what the instrument is looking at. Unlike ordinary, visible light, moreover, microwaves pass uninterrupted through clouds and are not dependent on sunlight, so there’s no interruption in the data-gathering during overcast days or at night.

Defense Meteorological Satellite Program (DMSP) satellites: Launched in June, 1987, the F8 satellite, part of the DMSP series, carried aloft a more advanced microwave instrument known as the Special Sensor Microwave Imager, SSM/I. which also flew on a number of subsequent DMSP satellites.

Aqua: Launched in May of 2002, Aqua carries a microwave imager from Japan called the AMSR-E, which stands for Advanced Microwave Scanning Radiometer for EOS (which stands for Earth Observing System). It works in a broadly similar way to SMMR and SSM/I.

The 1979 data in this animation come from Nimbus 7, data for 1989 and 1999 from the DMSP satellites, and the 2009 data from Aqua.