Scientists observed the bleaching of Australia's Great Barrier Reef early this year using satellite images. While capturing these events from space has been difficult in the past, Sentinel-2's frequent revisits and its resolution makes it possible.

The corals of the Great Barrier Reef have now suffered two bleaching events in successive years. Experts are very concerned about the capacity for reef survival under the increased frequency of these global warming-induced events.

Bleaching happens when algae living in the corals' tissues, which capture the Sun's energy and are essential to coral survival, are expelled owing to high water temperatures.