Things that would render Earth less then habitable

Exactly what it says on the tin. Specifically, I'm after something that we'd be able to see coming years in advance, would last quite a while, and preferably something that would seriously bugger up the climate

A meteor strike. It's unlikely, but possible (and we don't really have the technology to do anything about it if we spotted one approaching, even if we had a few years before it hit).

Well, global warming is an obvious choice, provided you don't go all The Day After Tomorrow. Since the rate of climate change hasn't been perfectly predictable, you could have someone suddenly discover that things are about to get a whole lot worse really fast.

edited 25th Aug '12 7:35:42 PM by Durazno

You could always go old school and pull off a good old fashioned nuclear war. (Though it is a tad vulnerable to Science Marches On. A lot of evidence suggests even in the worst case possible for nuclear exchanges no "nuclear winter" will occur.)

true, but the affects of the radiation on plant and animal life would be catastrophic, and I imagine that in such a case a nuclear famine could be very likely, and those able to get food would be liable to heavy metal and radiation poisoning in the long term.

Perhaps the mutations of virus, bacterium or plain old cross contamination could result in a food shortage? I am unsure about the state of agriculture overseas, but most of Australia's agricultural prosperity relies on us being free of diseases which affect the food sources of other countries. If a condition such as foot and mouth disease or a pest like fruit flies were able to become established on the main land, the affects on the economy and national food supply would be catastrophic. If endemics like this affected multiple countries, the national economy could end up going to pot, and famines might occur on a global scale. If the situation continued to deteriorate, with agricultural activity declining civilization as it is known would dissolve. Granted, the adoption of alternative food sources would come into play and the would would probably sort itself out in time, but in the short term I imagine things would be rather dystopian.

Nukes probably wouldn't work with what I'm planning since that sort of thing tends to result in a LOT of bad blood and that, and the nukes themselves, wouldn't fit in with the rest of the backstory.

Biological stuff wouldn't really work either since I'm not aiming for 'dystopia' so much as 'Humans Are Survivors'. Plus I really need something that would make getting off Earth seem like a really good idea.

Currently it's sort of a mental tie between an asteroid impact or Yellowstone going boom.

edited 27th Aug '12 9:11:22 AM by Weaver

Yellowstone going boom would be a good idea, as its quite plausible and an event similar to the speculated yellowstone boom has happened in the prehistory. If I recall correctly it was an event that brought the Cambrian period to an end, but it's been a long time since I read up on it so I could be wrong. Not only was the smoke and carbon dioxide a huge factor, but the subsequent global rise in temperature caused huge amounts of methane (which had been frozen on the ocean floor) to vaporize which in turn caused a phenomenal spike in temperature and made the atmosphere very prone to combustion, which caused something of a vicious cycle as plant life was eradicated and the greenhouse affect continued to spike, killing yet more plants until a combination of forest fires, animal extinction and a long cooling off period helped the climate to stabilize again. There a lot of methane on the bottom of the ocean today, I'm not sure what the threshold is, but if it vaporized all at once it would spark a long, disastrous chain reaction.

edited 27th Aug '12 11:44:43 PM by Lockedbox

^ Permian-Triassic Event. Aka the Great Dying. Flood basalt in Siberia (the resulting plateau of which is still very visible today in the northern reaches of Siberia just east of the Ural Mountains) triggered with coal seam fires raised the temperature enough to cause methane hydrate stores the world over to sublimate into massive gas releases. The CO 2 from the eruptions and fires was a pittance in terms of climate change compared to the methane hydrate eruptions.

I've read that some evidence suggests there's not enough methane hydrate presently on Earth to cause a repeat of the P-T event even if the exact conditions happened again.

The Sun going supernova in a few billion years?