How are we screwed? Let me count the ways:

Thought I'd just make a nice little doom-and-gloom list, for posterity's sake.

All of the following are googlable and independently verifiable:

*Climate:
-It is the end of the Holocene, the unusually warm 10,000-year period in the global cycle of temperatures.
-Spring has been unusually late in coming. Record late snowfalls have been occurring in parts of the northern hemisphere.
-On the southern hemisphere, winter is unusually early in coming. New Zealand and Australia have already reported snow and hail.
-We may not be headed for just a Dalton Minimum, according to Tex Arcane, but a Grand Minima - in short, a major Ice Age. Think woolly mammoths.
-Competition for habitable and arable land is going to spike as the climate continues to cool.

*Famine:

-I've already covered this under this post, so you may wish to peruse it for the details. Suffice to say, it is not looking good.

*War and civil unrest:
-About one-third of US citizens believe that armed resistance will become necessary to protect freedoms in the next few years.
-46% of US citizens believe that the federal government is an active threat to their freedoms and liberties.
-I don't think I need to highlight the recent civil unrest in Sweden and the UK. Those are the current flashpoints; most of Northern Europe is under the same threat.
-Syria: the next assassination of Archduke Ferdinand?

*Environment:
-Most of China's cities, unlike the US, are competing for arable land. China does not produce enough food to feed its citizenry.
-China is literally being choked to death on pollution; expats toBeijing are being offered hazard pay; up to 90% of China's open bodies of water are too polluted to support life.
-Major aquifers and water sources, especially in the western US, are being rapidly drained into nonexistence.

*Pestilence:
-Dispensation of antibiotics like candies for any and all reasons has led to massive growth in drug-resistant pathogens, eg. TB.
-As an added corollary, thanks to the wonders of "free love", numerous STDs are becoming impervious to all drugs.
-Nothing may come of it, but it may be a good idea to keep an eye on the new viruses coming out of the Middle East.

*Economy:
-The US is in some deep shit, and rightly so.
-China is losing its only source of competitive advantage as average wages rise by double digits for the last three years running.
-China has been repeatedly proven to be "massaging" its economic data more than most countries do.
-Japan's Abenomics, especially when it comes to Japanese Government Bonds, looks set to enter a nice little spiral.
-As an added point to the above, the weakening of the yen may be the start of a bona fide currency war.
-Things are getting worse and worse in southern Europe; for example, Spain's youth unemployment is already as high as 60%.
-Indeed, the whole world looks fit to enter the shitter.
-Central banks around the world are buying gold like mad, as are private citizens.
-China is busy undermining the US dollar's status as world reserve currency, signing bilateral trade agreements at an increasing rate to bypass the US dollar. The same is going on with Russia and its trade partners.

*Demographics:
-Canadian research group Conference Board of Canada warns of economic crash due to population collapse in developed nations around the world.
-Thanks to the wonders of sex-selective abortion on demand, China's average male:female ratio is 1.2:1. This is made even worse in rural areas in which two children are allowed under strict conditions, making it 1.46:1 for the first child and 1.9:1 for the second. Attempts to export the surplus male population to west africa has not gone unnoticed by the natives there.
-India is not much better, with some states such as Punjab boasting 1.25:1 male:female ratios.
-The welfare states of the West which are essentially a ponzi scheme based off an ever-growing population will inevitably collapse. Social Security is already pretty much insolvent.
-Most of Northern and Western Europe are being flooded with immigrants from Africa. Islamisation is imminent. Say goodbye to your quaint "rights".

*General state of humanity:
-People are getting stupider, lazier, more morally adrift and more ignorant, being content to be hooked up to the soma drip. Learned helplessness is ubiquitous across all modernised cultures.
-The rate of technological progress in most areas, save a few exceptions like computing and mathematics, is retarding at an accelerated pace. Where technological progress once meant going to the moon, today it's a bigger iGimmick screen.
-People are becoming increasingly atomised and the loss of tribe is keenly felt, even if not consciously.

All this is just off the top of my head; I'm sure I could pull out more if I wanted to. But nevertheless, it paints a grim picture of our future. While no one will be able to give you an accurate date or even timeframe, the end is inevitable.

Bunker down, everyone.