Complex sentence: Radar measurements of the North Polar ice cap found the volume of water ice in the cap was 821,000 cubic kilometers (197,000 cubic miles): equal to 30% of the Earth's Greenland ice sheet.
Split into simpler sentences: Radar measurements of the North Polar ice cap found the volume of water ice in the cap was 821,000 cubic kilometers (197,000 cubic miles). That's equal to 30% of the Earth's Greenland ice sheet.