Set in the year 2015 A.D.

Every morning when you wake up from bed and look outside the window, you notice that the sky seems getting darker every day. We were told by the authority that there's no need to be alarmed, it's just cosmic dust from space. Suppose that the cosmic dust is unusually thick and currently is blocking 5% of the sunlight from reaching Earth's surface and the situation is getting worse ever since, what should we do to survive this ordeal without knowing how long will the night last? Scientist calculated that in a year time there won't be any day!

  • $\begingroup$ Who is the authority? For western nations, the time when governments were driving the news cycle are long gone. Now they are driven by the news. You mention that scientists calculated (and presumably communicated) the time limit, is there consensus among the scientific community? And will the light really drop to zero? $\endgroup$ – o.m. Aug 20 '15 at 6:14
  • $\begingroup$ @o.m. The government told NASA to handle the situation to avoid panic, NASA informs the news that there is no need for alarm. In the meantime the government work day and night (later night and night) to find a solution. $\endgroup$ – Magic-Mouse Aug 20 '15 at 6:20
  • $\begingroup$ @Magic-Mouse, do you assume that European, Russian and Chinese agencies tell exactly the same lie? Who coordinated that? $\endgroup$ – o.m. Aug 20 '15 at 17:11
  • $\begingroup$ How did all this dust get here, inside Earth's orbit, all of a sudden? If the solar system passed through a nebula, we's see it coming forever. And it would keep beyond the bubble of the heiliopause, anyway. $\endgroup$ – JDługosz Aug 20 '15 at 17:13

Since a variation of the Sun's output by as little as 1% is calculated to be enough to have driven known climate changes like the European Warm Period (Scotland was a wine making nation in the 1200's, and Vikings were farming in Greenland) or the Little Ice Age (the Thames river was frozen hard enough to have "frost fairs" held on the ice, ad George Washington could drag artillery across frozen rivers to gain some important victories in the Revolutionary war), then a 5% drop in sunlight would be absolutely devastating.

Even before the amount of sunlight dropped to 5%, the effects would be widely noticed: global cooling, freezing over of bodies of water in the winter hemisphere, changes in wind and rainfall patterns, disruption of larger scale cycles like the Monsoons. At the - 1% mark, we would be entering the Little Ice Age, and agriculture would suffer immensely, causing mass starvation, leading to civil unrest, toppling of governments and wars across the globe (consider that when a fraction of the US corn crop was diverted from food to ethanol production, it triggered riots in Mexico and many other nations of the world as food prices spiked, and this was only a percentage of a single crop. Now do this to every crop in every nation).

By - 2%, I suspect that the real Ice Age would be beginning, and most northern nations would start evacuating their people one way or another. You could get peaceful migrations or a return of the Vikings, depending on how desperate people are becoming. As global order breaks down due to food shortages, I would put my money on Vikings.

By - 5%, we would be seeing glaciation, widespread die offs of plant and animal life and widespread deaths of human populations. Some people would be reverting to a hunter gatherer lifestyle, while others would be huddling around makeshift emergency shelters (maybe the best ones would be by volcanos and other sources of geothermal energy).

If sunlight were to be cut off completely, then we would see an extinction level event similar to the great extinction at the end of the Cretaceous period. Most plant life would die, destroying the food chain and most large animal life as well. If the event were short enough, then life could restart with cockroaches and small furry mammals, otherwise we might get "Snowball Earth" inhabited largely by extremophile bacteria. Once the cloud passed and the Sun returned, the ice would melt and the process of evolution would restart. Based on previous experience, it might take 3 billion years just to jump from slime molds to multi-cellular organisms, which would be close in time (or maybe even just past) the point where increasing solar output wold make the Earth uninhabitable.



The Earth will soon be a dead planet. The oceans will freeze solid. The atmosphere will turn into liquid air rain. Some deep bunkers may be able to prepare for the catastrophe, but the limited time to prepare will mean that long-term even these bunkers will will succumb to the deep freeze.

If the dust period is short enough, some bunkers could conceivably survive long enough, but pretty much all infrastructure on the surface will be severely damaged if not outright destroyed.

I doubt we could make a workable replacement biosphere in the short time to prepare. Noah's ark was simple compared to the task facing the survival of the earth in 2015.

The 100% drop in solar that comes in 1 year, at the point the only heat source left will be thermal flow from the core of the earth which is about 4000 times less than solar flux. I am assuming that the earth is still a black body radiator and the only significant heat source left on the planet is heat flow from the interior. This is over 4000 times less than the solar heating.

A quick quick for black body temperature shows the earth will be about 35 degrees Kelvin at equilibrium so the final temperature is clearly cold enough to freeze solid virtually all of the atmosphere.

Currently mankind generates about one-third as much energy globally as comes from the interior, but as mankind dies off this necessarily goes to zero.

Mankind 15 TW, geothermal 47 TW, Solar 173,000 TW

Upon further reflection, a different set of assumptions leads to a completely different outcome. If the dust absorbs 100% of the sun and it completely encloses the sun, it will receive the entire output of the sun and re-radiate the energy as thermal radiation. For dust at equilibrium at the sun's surface the dust equilibrium temperature will be 6000K just like the sun's surface.

As you move away from the sun the equilibrium temperature of the dust will necessarily drop. Ignoring convection, the equilibrium temperature at the distance of 1 AU would be about 255 Kelvin. The earth would eventually reach a temperature somewhat above 255 K due to it own greenhouse effect -- since the frequency mix would be completely different, I won't guess what the final temperature would be.

As the incoming flux would be nearly uniform from directions, there would be no temperature differences between the equator and the poles or seasonal variations either.

All surface plant and animal life still die out because plant photosynthesis requires the high energy photons of the sun, not the infrared that would come from the dust.

Transitory effects could still be quite severe. But at least there would be some hope of a possibly survivable outcome for some small population.

  • $\begingroup$ The Earth's atmosphere is made up primarily of nitrogen (79%) and oxygen (21%), with trace amounts of other gases that we can likely safely ignore for now. Oxygen has a boiling point of about 90 K, and nitrogen has a boiling point of about 77 K. To get the effect you describe you'd have to drop the surface temperature to 90-95 K or lower. What is your basis for the assertion that a 5% drop in insolation would drop the surface temperature of the Earth by over 200 K, to levels far below those seen on Mars? $\endgroup$ – user Aug 20 '15 at 13:43

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