The blanket of sea ice that floats on the Arctic Ocean appears to have reached its lowest extent for 2011, the second lowest recorded since satellites began measuring it in 1979, according to a report released Thursday by the University of Colorado Boulder\'s National Snow and Ice Data Center (NSIDC). The Arctic sea ice extent fell to 1.67 million square miles, or 4.33 million square kilometers on Sept. 9. This year\'s minimum of 1.67 million square miles is more than one million square miles below the 1979-2000 monthly average extent for September -- an area larger than Texas and California combined, according to the NSIDC. While the minimum extent was greater than the all-time low in 2007, it remains significantly below the long-term average and well outside the range of natural climate variability, according to scientists involved in the analysis. Most scientists believe the shrinking Arctic sea ice is tied to warming temperatures caused by an increase in human-produced greenhouse gases pumped into Earth\'s atmosphere. \"Every summer that we see a very low ice extent in September sets us up for a similar situation the following year,\" said NSIDC Director Mark Serreze in a statement. \"The Arctic sea ice cover is so thin now compared to 30 years ago that it just can\'t take a hit anymore. This overall pattern of thinning ice in the Arctic in recent decades is really starting to catch up with us.\" The last five years have been the five lowest Arctic sea ice extents recorded since satellite measurements began in 1979, said CU-Boulder\'s Walt Meier, an NSIDC scientist. \"The primary driver of these low sea ice conditions is rising temperatures in the Arctic, and we definitely are heading in the direction of ice-free summers,\" he said. \"Our best estimates now indicate that may occur by about 2030 or 2040.\"