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The earth is migrating, somehow (it doesn't matter how, but it's not directly destructive) into a higher orbit over the course of a century.

Details:

  • The earth-sun distance will increase by 150,000 km (0.001 AU) per year until it is 1.1 AU in 2115.
  • This corresponds to a temperature drop of approximately 15C before accounting for feedback like increased ice cover reflecting more light.
  • Technological and scientific progress has stalled, so we're limited to what we have today or what we could build without significant R&D, but substantial resources.

(How) Can we counter this temperature drop, e.g. by enhancing the greenhouse effect?

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    $\begingroup$ We're already trying quite hard at this and some people still don't believe it'll work (though some other guys, uhm, well, what was the name? IPCC? claim that a significant increase is possible - not 15 °C). $\endgroup$ – Ghanima Jan 11 '15 at 22:41
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    $\begingroup$ possible duplicate of worldbuilding.stackexchange.com/questions/2479/… $\endgroup$ – Vincent Jan 11 '15 at 23:11
  • $\begingroup$ Yes, yes. I just forget to raise my sarcasm sign ;) At least our experimental work (on a global scale) with CO2 shows what effort is necessary to cause a certain warming. Other ideas are not that well tested, still worth a look - e.g. what has been proposed for terraforming Mars. $\endgroup$ – Ghanima Jan 11 '15 at 23:13
  • $\begingroup$ @Vincent I think this may be sufficiently distinct - it is about maintaining the climate on a currently inhabited planet, which permits solutions which require, for instance, millions of people, large amounts of fossil fuels, or even just preventing the negative feedback of more reflective ice before it takes hold. $\endgroup$ – frodoskywalker Jan 11 '15 at 23:22
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    $\begingroup$ I am voting to leave this open as the other question is about terraforming while this is more how adjust to a change in an already habitable planet. I think the fact that the OP mentions greenhouse gasses lends to the idea that it may be duplicate but there may be other options in this scenario. $\endgroup$ – James Jan 12 '15 at 18:53
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We do not really understand the climate well enough to tell how well we could compensate. However I checked the Wikipedia on Ice Ages and it seems there are quite a lot of things vaguely associated with starting and ending of Ice Ages. This would give us quite a lot of things to try and while it would require a detailed simulation to give a "maybe" level answer of if it would be enough, every little bit would help. And the disasters associated with the abrupt change in climate would probably have reduced the amount of people to support anyway...

Greenhouse effect

The obvious. Changes in carbon dioxide levels have been strongly associated with the starts and ends of Ice Ages and we already have and use the necessary technology on massive scale. And we have lots of carbon reserves even with current economics, with everybody motivated to not go extinct we could extract sea bottom methane clathrates and methane currently impractical to even properly study. And burning as much hydrocarbons as we can would give as lots of cheap energy for mega projects. Although we could simply release methane into the atmosphere, if we have no need for the energy.

Oceanic currents

These have an effect on sea ice in the Arctic and the Greenland glacier. Basically we'd want to increase the amount of warm water flowing in from the Atlantic. I have no idea how this circulation actually works, but it has been suggested the Bering Strait has an influence on this. We could either close it with a dam or make it deeper with small nuclear devices. Usually either would be insane, but desperate times...

Similarly the Panama and the Suez could be blasted open to adjust ocean currents, if simulations suggested that might help. Although even in desperate times these canals would probably be too valuable to mess with on the scale needed to make a difference. Maybe if models suggested the fall in sea level would make them unusable otherwise?

Glaciers

If you make the glaciers, mainly Greenland and Antarctica, darker by seeding them with large amounts of smallish black objects, they will absorb more heat. And manufacturing and spreading the "grit" gives a good excuse to burn lots of hydrocarbons. Benefit this has is that the polar regions are generally the most effective place to increase heat as the starting temperatures are lower.

Deserts

Sahara, Arabia, Kalahari, and Atacama get plenty of sunlight. And then they uselessly radiate it into space. In the real world this makes people wonder about large scale solar power. With global Ice Age threatening people would be thinking about collecting the heat and using it to warm the planet. It is possible, although ridiculously expensive, to build huge networks of heat pipes connecting these deserts with nearby seas. Then you just fill the deserts with radiators that connect to the heat pipes when the temperature is high enough. Although the scale, and hence the cost, is astronomical, this has two advantages. It is simple, potentially zero moving parts and relatively cheap materials, so the maintenance costs once it has been built might be tolerable. More importantly it can be adjusted as needed in real time, which is a good feature to have, if you are meddling with the global climate on a massive scale. Which in this scenario we would be doing, anyway.

Orbital changes

While we can't really do anything about these, it is good to remember orbital effects other than the distance have a significant, if little understood, effect on global temperatures. Since we are, in theory, currently in the middle of an ice age and the change of orbits would almost certainly also mess up these cycles, it is possible there would be some warming effects from the change.

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Even limited to today's technology, platoons of mirrors could be lofted into orbit to add energy to the Earth's climactic system. Elon Musk's "SpaceX" is already building rocket motors on an assembly line (each Falcon 9 needs 9 Merlins on the first stage and one more on the second stage and the Falcon 9 Heavy will use two strap on Falcon 9 first stages, for a grand total of 27 rocket engines), and since the rocket engine is by far the hardest part of building a rocket, we are already cooking with gas.

Orbiting mirrors can be gauze like structures of aluminum foil in high or even geo synchronous orbit, so there is little difficulty there either.

The real problem is since we really don't understand how climate works, and climate is a non linear system governed by chaos theory, adding energy via solar mirrors will produce all kinds of unexpected effects (the old story of a butterfly flapping its wings in Peru causing a tornado in Texas). Local "hot spots" created by the mirrors will be surrounded by chaotic weather systems, and most of these will probably end up overwhelming the hot spots, negating the desired effects.

This means the other solutions would have to be humans burrowing underground, building greenhouses for agriculture, carrying out large scale genetic engineering so plants and animals can survive the colder climates and some percentage adapting to a neolithic hunter gatherer lifestyle like the Inuit. Each of these solutions has issues of its own, and there will be many sub groups carrying out different solutions, so hundreds or a thousand years after your event, hunter gatherers might be raiding greenhouses and hunting feral mutant goats and cows which had escaped from the initial genetically engineered flocks far in the past, while human civilization living in underground cities at a constant temperature worked to stop the depredations.

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