Would it be the same as what is described in the Personal Consequences Thread whereas it ends up with a bleak world similar to that of "The Road" with people struggling for food and eating each other.
One could also wonder how soon this could strike, would this be something that we would see in a decade or so, or could it be just around the corner in let's say during the next month or so or during the next year at most.
I personally am not sure cannibalism is likely to be widespread. While you'll find historical precedent for it in certain circumstances (Holomodor for instance), I think you'll find more that indicate many (if not most) people starve before they will resort to cannibalism (even eating already dead people has a significant taboo against it).
With respect to how soon things could strike I think it is more helpful to identify key events in the processes at work (given the issues in crystal ball gazing). For example in 2010, following a severe heatwave, Russia stopped exporting certain crops to preserve supplies for the domestic market. Who needed to buy that food? Arab spring countries... look how fast the knock on effect of rising food prices in the importers hit? Accordingly I think countries applying blanket export bans on food is a definite thing to watch for. I feel we dodged a bullet somewhat last year in this respect as despite bad harvests in many regions we didn't see this as I expected (Russia for example also had a heatwave/drought last year). Obviously substantial net food importers feel the sharp end of this particular wedge, and much depends on the resilience of their society at the time (the economic crisis doesn't help - though it is all interrelated).
The risk if you live in a net food exporter is a little different. Whether or not you have a food problem then depends upon your affluence and the government. If big business (backed by government) is happy to sell the food the nation needs to feed itself to other people in other countries with deeper pockets - then you can still end up with hunger at home. As social inequality bites this will cause issues of a more gradual (but just as dangerous long term) nature. I think an informed policy would be to export what one can (as opposed to outright hoarding and blanket export bans) but to make sure national stability is preserved.
Consider key vulnerabilities in the complex globally interdependent world we've constructed (which I personally think is far more fragile than people tend to think). If one failed state (Somalia) can cause so many issues to global trade through piracy - how many failed states next to key trading routes do we think we can handle without wider problems? Will cargo ships still sail unmolested if wars break out in those regions? How much military force is available to try to secure those trade routes (considering the other demands likely to be made of the military)?
Consider the risks posed by social unrest in oil exporting nations (who also wield disproportionate influence through the dependency of importing nations). Energy prices feed heavily into the prices of everything else including food. The collapse of key oil exporting countries is therefore another thing to watch out for, bearing in mind how little spare margin of production now exists (economic crisis notwithstanding - and indeed the persistence of which partly itself relates to the cost of energy!). I know people grasp at the notion of it being good to burn less fossil fuel - but I submit that the operation of modern civilisation inherently depends
upon it currently.
There are any number of other key resources produced in specific regions and transported globally. Agricultural inputs for example. As a somewhat flippant example of the sort of knock on effects I think can propagate quite fast:http://www.firstpost.com/tech/hard-disk-drive-shortage-hits-manufacturers-retailers-and-you-140412.htmlhttp://www.computerworld.com/s/article/9222522/Impact_of_hard_drive_shortage_to_linger_through_2013
So floods in one region in one year affected the global supply of hard disks for several years? Did you see a rush to construct factories in other nations to reduce dependence? How does that sit with regional extreme weather events plus adversity in trading and further economic decline?
Then there are the giants, whose fall I think will shake the world. Consider the logistics of trying to run China (and what happens to the rest of the world suddenly unable to import their stuff if they fold?). How do you keep juggling all those plates? If the land rush in Africa that has been going on for a number of years now culminates in the failure of large swathes of Africa - will they have to use the military to secure those food production sites? What lengths is the Chinese government prepared to go to to keep the population under control? Is there a danger war can become a convenient focal point in that process - nations often like to externalise their difficulties if they can (blame anyone but the government!).
I don't really expect an all out nuclear war - not that many countries have that many bombs. The two that notably do are large agricultural exporters with favourable population densities and the deterrent value is key there. I'd be a little surprised if nobody used anything nuclear (look how many people have or are trying to get them now...) - but bear in mind they wouldn't be the first nuclear bombs used. The use of biological weaponry feels a bit more likely as you have scope for a lot more plausible deniability (if a pandemic breaks out somewhere, who can say it was caused deliberately?). Even this I think is a fringe possibility (or option of last resort) - biological weapons carry plenty of drawbacks of their own.
I think people also seriously underestimate the human factor. It's easy to look at a single issue - climate change - and conclude that it will take a fair amount of time for impacts to come through. Above and beyond the argument I'm making that people ignore an awful lot of other issues that form part of the overall puzzle - we need to consider people are forward looking.
If you know that a company you have investments in (for those lucky enough to be so rich) is going to go bankrupt - do you wait until it does to offload your investments? What sort of effects do we think will occur sociologically as it dawns upon people in the wider sense that the writing is very clearly on the wall? How will that affect the economy? Will people try to hoard resources and self fulfill a prophecy of violent collapse in competing to do so even before the pressures are so great they would be driven to extreme means of surviving anyway? Isn't panic itself also a thing to be concerned about therefore? Speculation? The futures markets?
For all these sorts of reasons (and more) I think our modern civilisation is a complex fragile tangle of positive feedback waiting to happen. I think the fragility of current civilisation should not however be conflated with the inherent resilience of our species (notwithstanding the severity of the threat).
I am aware that my outlook is a lot bleaker than most people are willing to consider. If people want to say "I think you're wrong", that's fine. What would be even better is if they could hold up a rationally driven debate explaining precisely why they think I'm wrong (ie a bit more than just "I think" or "I hope"). I'm always open to learning new things and I have made some certain key assumptions in all this (for instance in relation to the severity and rate of agricultural problems as the Arctic melts out).
I'm not a professional climatologist, or even academically educated to degree level in anything. Accordingly my opinions can be easily dismissed and arguably deserve no more consideration than the guy muttering into his beer next to you in the pub.
A couple of quotes I find apt:
"the fundamental interconnectedness of all things" - Dirk Gently - http://en.wikipedia.org/wiki/Dirk_Gently
"Whoever fights monsters should see to it that in the process he does not become a monster. And if you gaze long enough into an abyss, the abyss will gaze back into you." - Friedrich Nietzsche