The University of Colorado at Boulder's National Snow and Ice Data Center said Arctic sea ice on Sept. 16 stood at 1.59 million square miles, about 1 million square miles less than the long-term minimum average from 1979 to 2000. Scientists compared the loss to an area about the size of Alaska and Texas combined.

The sea ice is at its lowest level since satellite record-keeping began nearly 30 years ago, the university said Friday in a release.

Scientists blame the declining Arctic sea ice on rising concentrations of greenhouse gases that have increased temperatures from 2 to 7 degrees Fahrenheit across the arctic and strong natural variability in Arctic sea ice, the researchers said in a release.

Arctic sea ice melts each summer, reaching its minimum extent in September and its is usually at maximum area in March.

The researchers used satellite data from NASA, the National Oceanic and Atmospheric Administration and the U.S. Department of Defense, as well as data from Canadian satellites and weather observatories for the study.