Short answers, pulled from the story.
The Greenland ice sheet is the second-largest body of ice in the world. It averages 1673 m thick and exceeds 3488 m at its maximum, stretches almost 2900 km north to south with a maximum width of 1100 km, and covers 1710000 km2, around 80% of the surface of Greenland.
If all 2900000 km3 of the Greenland ice sheet melted, global sea levels would rise by about 7.4 m. The sheet has already contributed 1.4 cm of sea level rise since 1972.
A single ice sheet first covered most of Greenland some 2.6 million years ago, after atmospheric carbon dioxide fell to between 280 and 320 ppm around 2.7 to 2.6 million years ago. Greenland had carried major glaciers and ice caps for at least 18 million years before that.
The Greenland ice sheet is melting two to five times faster than before 1850, driven by warming that is amplified in the Arctic. Warming North Atlantic waters melt glacier fronts from below, surface meltwater lubricates glacier beds through moulins, and darker algae and melt ponds reduce albedo and accelerate melting.
A temperature of -69.6 C was recorded on the 22nd of December 1991 at an automatic weather station near the topographic summit of the Greenland ice sheet. It is the lowest temperature ever recorded in the Northern Hemisphere, a record recognized only in 2020.
Camp Century is a former United States military site built to carry nuclear weapons for Project Iceworm. The project was cancelled and the site was never cleaned up, and it now threatens to release nuclear waste, 20,000 liters of chemical waste, and 24 million liters of untreated sewage as the ice melts.