In a scant four days this month, the surface of Greenland’s ice sheet melted to an extent not witnessed in 30 years of satellite observations, NASA reported on Tuesday.

On average, about half of the surface of the ice sheet melts during the summer. But from July 8 to July 12, the ice melt expanded from 40 percent of the ice sheet to 97 percent, according to scientists who analyzed the data from satellites deployed by NASA and India’s space research institute.

“I started looking at the satellite imagery and saw something that was really unprecedented” since the advent of satellite imaging of the earth’s frozen surface, or cryosphere, said Thomas L. Mote, a climate scientist at the University of Georgia who for 20 years has been studying ice changes on Greenland detected by satellite.

While scientists described it as an “extreme event” not previously recorded from space, they hastened to add that it was normal in a broader historical context.