Absence of clouds caused pre-human supergreenhouse periods

In a world without human-produced pollution, biological productivity controls cloud formation and may be the lever that caused supergreenhouse episodes during the Cetaceous and Eocene, according to Penn State paleoclimatologists.

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<p><a href="http://www.physorg.com/news127055403.html">Absence of clouds caused pre-human supergreenhouse periods</a></p> <p>In a world without human-produced pollution, biological productivity controls cloud formation and may be the lever that caused supergreenhouse episodes during the Cetaceous and Eocene, according to Penn State paleoclimatologists.</p>