Global warming isn't happening on Mars, so face up to it on Earth. That's the conclusion of an analysis of the Red Planet's melting polar ice cap, which shows that Swiss-cheese-like pits forming in the ice are part of a natural cycle, not unusual warming. The pits were first spotted at the carbon dioxide ice cap at the Martian south pole in 1999, then pictured again in 2001, one Martian year later. Comparing the images revealed the pits had grown by a few metres. At that rate, the entire ice cap would disappear in a few thousand years. Some climate sceptics suggested this meant our neighbouring planet is undergoing global warming just like Earth, so the sun - not humans - must be behind warming on both planets.
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