Greenland's ice sheet is driving global sea level rise. One section is melting 80% faster.

Average temperatures around the world may be slowly ticking upward, but their effects on the environment can be sharp and quick.

Earlier this week, we learned that Arctic sea ice extent is declining at its fastest rate in 1,500 years. On Wednesday, scientists reported that in 2003, the ice sheet on Greenland suddenly began melting at a much faster rate.

Greenland’s ice is hugely important for the planet. The sheet of ice that covers 660,000 square miles is more than a mile thick and has a volume of 684,000 cubic miles.

If it all melts, it would raise global sea levels by 25 feet. On Thursday, scientists published a new map of the land mass beneath Greenland’s ice, showing that the ice is deeper than previously thought, so losing it all would lead to an additional 2.7 inches of sea level rise above past estimates.

Already, about 269 billion tons of ice have melted away each year since 2002.

In a paper published Wednesday in the journal Science Advances, scientists reported that in one catchment in Southwestern Greenland, the melt rate surged 80 percent between 2003 and 2014 compared to the 26-year period beforehand, hinting at changes in the overall melt rate of the ice sheet.