New Delhi, Sept. 22 -- IN APRIL the crew of Artemis II showed that Earth's loveliness from afar, originally revealed by the Moon-bound Apollo missions of the 1960s and 1970s, remains one of the space age's enduring truths. The home planet's intricate, swirling, colourful complexities turned out to offer just as wonderful a contrast to the sloe-black of space and the drab dull Moon today as they did when seen half a century ago.

More prosaic observations from space, though, reveal a disturbing change. They show that the brightness with which that beauty burns is dimming. Seen from afar, Earth is looking steadily darker.

Evidence of this dimming comes from a project called Clouds and the Earth's Radiant Energy System (CERES). Since the en...