<http://schema.org/articleBody>
"  Ice in the Arctic Ocean has hit a new record low, dropping just below 1.66 million square miles in extent for the first time since 2007. The ice will continue to shrink for a few more weeks, setting additional records until it hits its minimum for 2012 sometime in September.  Sea-ice extent is often cited in discussions of climate change. These days it figures into geopolitical discussions, too, as Arctic nations and private companies plan for increased oil drilling, tourism, freight traffic, and military activity in the region. Coast Guard officers, Inuit whalers, and oilmen agree that summertime Arctic ice is retreating rapidly. But the National Snow &amp;amp;amp; Ice Data Center, based at the University of Colorado in Boulder, provides hard numbers to back up those personal observations. Here&amp;#039;s how the NSIDC does it. Satellite-borne sensors collect data by recording microwave emissions from the ocean surface. This a useful spectrum for studying ice, NSIDC scientist Walt Meier says, because the emissions from ice and water are easy to tell apart. Additionally, they are independent of sunlight, passing through clouds easily. The space-based sensor has a fairly coarse resolution. If you think in digital terms, each pixel is a circle on the ocean surface 30 miles (50 km) or more in diameter. At least 15 percent of the area has to be covered for it to count as &amp;quot;ice&amp;quot; in the data. The satellite circles Earth about 14 times a day in a polar orbit, reaching a latitude of approximately 80 degrees. (It doesn&amp;#039;t see all the way to the north pole.) Each pass covers a swath of the Arctic Ocean, and the sat surveys the entire area at least once and sometimes several times a day. The swaths overlap; stitched together, they provide an overall picture. &amp;quot;The daily composite isn&amp;#039;t an instantaneous snapshot of the sea ice,&amp;quot; Meier says. &amp;quot;Some of the data may come from the morning and other data from the afternoon. But the sea ice doesn&amp;#039;t change very quickly.&amp;quot;  Hitting a new record minimum for ice extent guarantees lots of media coverage every few years, but it&amp;#039;s not a particularly significant milestone. What&amp;#039;s more interesting to scientists is that the past six years have seen the lowest sea-ice extents since satellite measurements began. Satellite observations began in 1979, and sea ice has retreated by about 40 percent compared with the commonly used baseline period of 1979 to 2000. &amp;quot;The big picture is the long-term trend,&amp;quot; Meier says. &amp;quot;This isn&amp;#039;t a quirk or an extreme event.&amp;quot; Scientists have several ways to puzzle out an extended history of Arctic Sea ice before 1979. They can use limited satellite data from the 1960s, along with operational ice charts created to support shipping. These date back to the early 1950s for the entire Arctic, and to the 1920s and 30s for Canadian and Russian waters.  To look still further back in time, researchers consult historical surface temperature readings, written records, and a growing collection of sediment cores taken from the seafloor. During the Medieval Warming Period of the 10th to 12th centuries, the North Atlantic was nearly as warm as it is today. According to Meier, however, scientists estimate that Arctic Sea ice last reached the current low level during the Holocene Thermal Maximum, 8000 to 10,000 years ago, when temperatures rose sharply after the end of the most recent ice age. "^^<http://www.w3.org/2001/XMLSchema#string>
<http://www.popularmechanics.com/science/environment/a8033/arctic-sea-ice-to-hit-a-new-record-low-12108429/>