No sunlight

Your body needs sunlight to get enough vitamin D. Your characters would have to eat a lot of foods rich in D to compensate, such as: fish & liver. Without enough people can get softening of the bones or if they are also low in calcium - rickets. Not enough vitamin D could lead to dental problems, fragile bones, being shorter in stature.

Not sure how long until all/most of the plants die, but once they do the herbivores will die off, and then there will be a drop off in the carnivore population - those who aren't eating the humans that is.

Some people will suffer depression, may even become suicidal. Depends on what your population does to compensate for the lack of natural light. People might start falling into their circadian sleep/wake rhythm. Most people's bodies don't naturally run on a 24 hour clock. You might want to research how people close to the Arctic circle cope during the winter. It's not complete darkness, but it might give you some ideas that you could expound upon.

Weather is largely affected by the heating and cooling of the earth's surface. Without changes in hot/cold there might be no wind. As it grew colder, water would evaporate more slowly, so it would rain less and less often. No dew, no natural condensation. Again, may be affected by the technology in your world. The planet would definitely get cold, very, very cold. It would take a while because our atmosphere helps hold in radiant heat, but eventually this would escape into space. Think moon cold.

Good luck, sounds like an interesting concept for a story. Hope to see part of it someday!

Here is a good starting point: http://en.wikipedia.org/wiki/Nuclear_winter

Basically, the surface would freeze after a few days. Plants wouldn't last more than a couple of weeks, and animals that didn't die of cold would starve.

In people not exposed to sunlight and not eating vitamin D-rich foods, vitamin D deficiency could occur after 4-5 months or so (after the vitamin D body stores are exhausted):

In the northern hemisphere, people who live in Boston (U.S.), Edmonton (Canada), and Bergen (Norway) can't make enough vitamin D from the sun for 4, 5, and 6 months out of the year...The body stores vitamin D from summer sun exposure, but it must last for many months. By late winter, many people in these higher-latitude locales are deficient.

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Source (harvard.edu)

Symptoms of vit. D deficiency in adults include muscle and bone pains, increased frequency of bone fractures (due to soft bones - osteomalacia). In children, rachitis (deformed bones) is most characteristic.

Vitamin D, like mentioned, is in fish and fish liver oil. In the U.S. and Canada, pretty much all commercial milk is fortified with vitamin D. Other common vitamin D fortified foods: orange juice, ready-to-eat cerelas, margarine. Vitamin D supplements in oral and injection form are available. Foods with vitamin D could prevent or postpone the onset of vitamin D deficiency in some, but probably not all, people.

Sleep

Dark stimulates the release of the hormone melatonin, which induces sleep and daylight inhibits melatonin release and thus helps to maintain wakefulness. Sunlight deprivation would result in sleepiness, fatigue, depression. You can search for "seasonal affective disorder" or SAD (basically, some people are more depressed during winter).

You should read this:

https://en.wikipedia.org/wiki/Year_Without_a_Summer

In this case the amount of sunlight was decreased due to climate changes and a rather big volcanic eruption. It will show you what effect just diminished sunlight and a drop in temperature will create. Where I live it snowed in July. (According to town records of my home town.) (And for those who don't know New England, the avg. temp. in July is around 75-80 F. And this July, 2012, was our hottest July ever.)

So complete darkness? Absolutely devastating, imo.

Fascinating as it may be, I think everything - and I mean everything - would crunch to a halt. For a kick-off, would you go to work as normal leaving your family at home not knowing what the hell was happening or why there was no daylight? I wonder how long energy/power supplies would last if used 24/7.

No idea how this would work into a story unless it was known pretty quickly why the darkness was there so there was a known problem to be overcome.

Good luck.

Sat Nam! (literally "Truth Name"--a Sikh greeting)

Cold. Cold. Cold. And no photosynthesis, so no oxygen. We wouldn't last long, unless it was brief.

Blessings,

Siri Kirpal

Just saw this very apt article on Slate.com today!

Underground and Under the Weather: How Long Can You Live Without Sunlight?

Being deprived of sunlight is not the same as there being no sunlight globally.

lac582 said:

Just saw this very apt article on Slate.com today!

Underground and Under the Weather: How Long Can You Live Without Sunlight?

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Bufty said:

Being deprived of sunlight is not the same as there being no sunlight globally.

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True. I just thought it might add to the discussion.

People and animals who live in the far north can do without sunlight (or with very little and very weak sunlight) for four or so months of the year. Certain plants and animals are adapted for this. But in the long term, nothing but cave dwellers and subterranian beings would probably survive. People in polar regions survive on meat, but if this were long term, that wouldn't work.