An envelope http://al4a.fun/ al-4a NASA regularly records the extent of the Arctic sea ice. Monitoring its extent is crucial for better understanding how the melting ice can impact our world. Researchers employ satellite imagery, submarine sonar and data collected from NASA's Operation IceBridge, an airborne survey of polar ice. Yet while researchers found that the extent of the ice stretched far further than previous years, its thickness was much less. In fact, scientists discovered that the ice thickness is as much as 50 percent thinner than it was in previous decades, going from an average of 12.5 feet in 1980 to 6.2 feet in recent years.