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Let's pretend the clouds got there via magic or some bizarre scientific experiment gone wrong. The why isn't important for the question.

Question: How would the earth be affected if its entire sky was constantly covered in clouds dense enough you couldn't see sky beyond them? Would life survive? How would plants be affected?

(Let's assume that rain and storms still occur in roughly the same way.)

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    $\begingroup$ Look into nuclear winter which is a less extreme version (the sky is not completely blocked out) of what you propose. $\endgroup$ – Schwern Jun 6 '16 at 5:16
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The end is nigh

Permanent total cloud cover means that the planet is about to undergo thermal runaway. Soon the oceans will boil and Earth will be a cooler version of Venus.

For most of geological history there was no ice at sea level anywhere on earth and Earth was warmer than today. Temperature was well regulated by cloud cover. If Earth got warmer more water evaporated and more clouds formed. Clouds reflect sunlight back into space before it can warm the Earth. So there is a negative feedback loop stabilising the temperature.

The negative feedback ceases when cloud cover becomes total. The end is nigh.

In passing, global warming worries relate to melting the current ice and disrupting the present (unstable) interglacial climate. That would be pretty catastrophic, but life and probably even human life would survive.

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  • $\begingroup$ This is completely backwards. Cloud cover increases albedo. Venus' albedo is 0.75; Earth is 0.30. This means that Venus receives LESS solar radiation energy than Earth. You can calculate from the Effective Temperature equation yourself. If clouds magically covered all of the Earth, there would be runaway global cooling. $\endgroup$ – kingledion Mar 12 '17 at 2:03
  • $\begingroup$ @kingledion I can assure you it is not nonsense. Google "cool Venus". Water vapour is both the source of clouds which reflect sunlight, and a greenhouse gas. Until cloud cover reaches 100%, reflection dominates and the feedback is negative. More heating, more water vapour, more clouds, more sun reflected, temperature falls back, more condensation, more rain, cloud cover falls back. Stable. After 100%, reflection cannot be increased by adding water vapour and the feedback becomes positive. More water vapour, more greenhouse heating, more water vapour ... until the oceans boil. $\endgroup$ – nigel222 Mar 14 '17 at 9:00
  • $\begingroup$ "Cool Venus" is one of the two possible fates of the Earth in the deep future as the sun ages hotter. The other is that water vapour, being lighter than oxygen and nitrogen, is lost into space fast enough that the planet will be dessicated into a hotter version of Mars by then. I think most research favours the latter. Anyway, it won't happen for a good few hundred millions of years, even if humanity does emit enough CO2 to cause all the ice to melt. $\endgroup$ – nigel222 Mar 14 '17 at 9:24
  • $\begingroup$ You are interpreting the problem statement incorrectly. The OP proposes a 'magical' step increase in cloud cover. As you say yourself, the feedback is negative in the range of <100% cloud cover. This negative feedback will cause a corresponding step decrease in temperature. $\endgroup$ – kingledion Mar 14 '17 at 14:20
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    $\begingroup$ I think that the question has been edited since I read it! $\endgroup$ – nigel222 Mar 14 '17 at 15:04
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There is life in caves, there is life at undersea volcanic vents. Surely there would be life under the clouds.

  • The clouds should affect the climate and that affects the generation of new clouds. Pretend that doesn't happen. Enough thermal energy gets through to keep the current temperatures.
  • Direct sunlight will be reduced. Plant grow will be reduced, but you can get some plants to survive indoors on artificial light, too.
  • With fewer plants, there will be fewer herbivores and fewer carnivores. For omnivores like mankind, there would be widespread famine but no extinction.
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