DECEMBER normally makes me happy. I love shopping and I love eating, so the idea that Christmas is just round the corner is enough to cancel out pretty much any amount of misery. But not this year.

For starters, with retail sales so weak, shopping just isn’t as much fun as it should be. Last week I popped into an Oasis store to have a quick look round and found that not only was I the only person in there but it seemed they weren’t expecting anyone: the changing rooms were roped off and the staff were sitting about listening to a mournful manager explaining that sales were down 5% on 2004. I bought a dress just to try and cheer us all up.

Then there is the avalanche of bad news in the papers. Who could possibly feel even faintly optimistic about the future after they have finished reading the business pages these days — particularly if, like me, you read all the papers and hence end up reading the bad news five or six times over? The most depressing news is, of course, about pensions. It seems there is no way round it, we are going to have to work longer and pay millions more in tax for the privilege of doing so.

But the bad news does not end there. There is low consumer confidence, concern about inflation and interest rates and unemployment to think about, too. British Airways is said to be eyeing up the future of 15% of its 46,000 employees, and we can surely expect to see layoffs from some of the retailers soon. How long can the likes of B&Q cope with profits falling 50% year on year without taking a good look at staff costs? It’s all worrying.

But take a look at two new business books, and you will find that the things I am concerned about are small beer compared with the things the real pessimists have on their minds.

Just out is a book from Bill Bonner, Empire of Debt, which tells the story of how all empires are eventually undone by the same “vain overreaching”. The American empire is a “commercial empire”, says Bonner, and these work only for as long as the empire’s homeland industries have a commercial advantage over the rest of the world. When that is no longer the case — as with Britain at the end of the 19th century — commercial empires tend to fall back on debt to finance themselves.

That is exactly what is happening in the US right now. America is spending more on its military than the rest of the world combined, yet it hasn’t any money left. So “in order to bring liberty and democracy to the world”, it has to borrow from everyone else, selling its bonds to the Chinese, for example.

Can it ever pay them back? Not in real money, says Bonner. The US no longer has a competitive advantage in anything, the Asians do and that means the current situation is unsustainable. One day the Asians will get fed up and stop lending to the Americans and the empire will come tumbling down. Look out, says Bonner, for the dollar to collapse as a result and the US economy to follow.

But Bonner isn’t the biggest worrier in the market. Also just out is Wake Up by Jim Mellon, chairman of Charlemagne Capital. Mellon comes across on first meeting as a calm and contented sort of a man. But a quick read of his book shows you he is nothing of the kind.

Instead he is a nervous sort. Mellon agrees that economic leadership is in the process of shifting from West to East and points to the sorts of financial imbalances that bother Bonner — the record levels of fiscal, trade and personal debt in the West. But he sees the globe’s problems as running even deeper than Bonner does: due to the widening gap between the rich and poor across the world he expects to see further “disaffection, anti-western sentiment and religious fundamentalism” leading to non-stop rounds of terrorism and the end of peace.

Add it all up and “the unparalleled prosperity enjoyed by western nations over the past 50 years is unsustainable”, says Mellon. Expect asset prices to fall dramatically and “world trade conditions to deteriorate”.

Not all these predictions are completely convincing, but, under all the apocalyptic language, much of it is fairly sensible commentary.

Take the dollar. The deficit problem has been undermining the US currency for years, but despite all expectations to the contrary it hasn’t collapsed yet. According to the optimists, this means that it is less likely to happen, that all the worrying is for nothing. This is nonsense. It is like saying that just because you have not died yet you probably won’t.

We cannot say when it will happen, but it is inevitable that a huge financial crisis will one day come to America.

So what do you do about it? The two authors agree on this bit. Buy real assets — things that won’t lose their value as western currencies do, in particular gold, silver and diamonds. The good news is that, whether the global economy implodes or not, this is fine advice. All three commodities have tight supply-and-demand conditions so they should work for you either way: if there is no crisis, they will probably turn out to be good investments, but if there is, they will turn out to be great ones.

Merryn Somerset Webb is a former stockbroker and now editor of Money Week. Her views are personal and investors should always seek professional advice