Also show are agricultural land use and land surfaces with little or no plant cover - such as bare ground, urban areas and permanent snow and ice.

BBC: How Earth's land is used

Of these freshwater resources, about 24 million km3 or 70% is in the form of ice and permanent snow cover in mountainous regions, the Antarctic and Arctic regions.

FORBES: Connect

To assess the contribution from melting ice sheets, scientists try to measure "mass balance, " which is the difference between the annual snow that falls on the permanent ice sheets each year, and the total mass of ice that melts or breaks off the sheets.

WSJ: Polar Ice Sheets Melt at Faster Pace

This would force a hiring freeze and the furloughing of permanent staff, as well as delay spring openings of the park to save money on costly snow-ploughing operations.

BBC: US national parks under threat