Dr. Doom is back. Last week, New York University economist Nouriel Roubini decided to speak out about the current economic recovery, warning that it cannot last. I'm not quite sure how this blog missed my radar screen, so I must thank Robert J. Samuelson for bringing it to my attention yesterday.

Roubini contends that while there was a massive rally in "all sorts of risky assets" has caused the dollar had weakened sharply and government bond yields have "increased but stayed low and stable." These risky assets that Roubini discusses are equities, oil, energy, and commodity. Dr. Doom believes that the prices for these risky assets have risen too far and too fast compared to macroeconomic fundamentals.

We're tired of bubbles, right? Anyone 30 or older has lived through two big ones so far, with a brief period of prosperity separating the decimation of dot-com largesse and mortgage-fueled paper wealth. It could take until 2014 for the jobs lost to be replenished, and there's little reason for optimism.

So, with the economy in the tank, we can focus elsewhere -- maybe on saving the planet. If we can't put green in our wallets, maybe we can add some to our lifestyles. Or, you could do both. Green technology could be the next boom in the United States, even if we do lag some parts of the world, and investing in clean solutions is really nothing other than investing in the next big thing. Even if you don't give a damn about climate change (or don't think it exists at all), the green market could likely become your employer -- or trigger the economic growth that will create your next job.

Some signs are visible already.

There was a very interesting piece written by Karen Blumenthal in The Wall Street Journal yesterday. Blumenthal takes a look at the Beanie Baby craze and how we can all learn from the "Beanie Baby Bubble." Blumenthal has studied bubbles and has determined that there is a pattern that drives these economic phenomena - be it Beanie Babies, real estate, or "Dot Coms."

Blumenthal contends that bubbles need these characteristics: fertile ground, people getting on board, ignoring warnings, greed, and an after-party. Think about the fertile ground, when Beanie Babies first came out, there was a fertile ground. Kids, parents, and grandparents were looking for a new toy, one that could be both a cherished heirloom and a cute adornment for mantles, dressers, and the back window of Cadillacs. The ground was fertile, and this group quickly jumped on board the Beanie Baby train and pushed the prices to a point where some people would pay upwards of $100 for a $5 bean-bag animal.

There is an unprecedented change in U.S. bond prices to the upside. As the old adage says: stocks down, bonds up. This has never been more true than this past year. With stocks falling sharply, bonds have been rising to astounding heights.

The price of bonds moves in an inverse direction to yield, so as yields come down near zero, bond prices go up. The Treasury Bill is now at a minus zero yield and the 30-year bond at 3%. Usually, the longer the term, the higher the interest rate because of the greater risk of holding an investment for 30 years.

As the stock market fell sharply over the last few months and the Federal Reserve has cut interest rates almost to zero, the prices of U.S. Treasuries has soared to new all-time highs. For example, the forward contract in the 30-year bond that is traded on CBOT (Chicago Board of Trade), in early October traded at 112 and has since risen to 135. To give you an idea of what this means, the price increased 2400 basis points. Each 100 basis points equal $1000.00. So one bond contract is now up $24,000.00.

This post is part of our feature on Money Winners of 2008. See all 20.

Lots of people thought real estate was overpriced. Many worried that banks were giving out mortgages too cheap. But what did you do about it? (Either to help the situation or to make money.) Jeff Greene, a real estate mogul in California, actually found a way to bet against the subprime mortgage folly. He made $450 million -- at least that was the count earlier this year.

Well, he didn't just think of it on his own. He basically took the idea that his friend, hedge fund manager John Paulson, had. Paulson thought that, as an individual, Greene wouldn't be able to do this complex a transaction. According to the Wall Street Journal he even used special software so investors in a hedge fund Paulson created just to exploit the subprime crisis couldn't pass on his strategy.

How Greene and Paulson made money involves two financial terms you've probably had to learn this year and never want to hear again. Collateralized debt obligations (CDOs) are the way mortgages are packaged and sold to investors in various slices of risk. Credit default swaps are the holders of those investments insured themselves -- by buying what was like unregulated insurance from one another. The credit default swaps are what got so many big companies in trouble -- they had to pay up on investments that went bad. So Paulson shorted CDOs and bought some credit default swaps.

Another day, another oil record.

Oil easily pushed past $145 Thursday morning after traders calculated that the already weak dollar has further to fall after the European Central Bank increased a key interest rate by a quarter point to 4.25%.

Oil rose as much as $2.28 to $145.85 per barrel -- an all-time high -- before easing back slightly to trade at $144.40 at mid-day.

Oil tends to rise when the dollar falls as investors/traders seek to preserve purchasing power of the decreased value of dollar-denominated commodities by bidding their price up. However, it's important to note that the dollar/oil correlation is not perfect: there have been instances in which the dollar fell and oil fell.

There's been a lot of talk lately about the housing bubble, and a lot of folks have been placing a lot of the blame on easy credit, subprime mortgages, and predatory lending.

It's entirely right they they should do this. The heady days of the bubble were marked by unprecedented access to credit for people with poor prospects and rampant mortgage fraud (often perpetrated by heavily-commissioned real estate brokers) further exacerbated the problem of people buying houses they really couldn't afford using gimmicky adjustable-rate and other toxic mortgages.

It's easy to see how this contributed to the bubble -- an avalanche of prospective home buyers armed with funny money drove up housing prices with little or nothing in the way of down payments -- the mortgages were wrapped up and sold to Wall Street, but that's another story. It's estimated by some that more than 20% of recent subprime home loans will end in foreclosure -- You don't need a Ph.D in economics to know that an influx of new homebuyers is going to drive up prices.

So here's my question: Was the first of the 2000s a housing bubble or a consumer credit bubble that drove up housing prices?

A quick look at Google: The phrase "Housing bubble" yields 1.22 million results. "Consumer credit bubble" brings up just 4,850 results.

I would argue that easy credit and lax lending practices were by far the most important contributor to the housing bubble -- it's hard to even think of anything else that comes close.

Maybe we should start calling it the "consumer credit bubble". After all, there were plenty of areas, almost exclusively those with a low incidence of subprime loans, that haven't had the wild gyrations in home prices and sales volume that have characterized this bubble.

The price of wheat says it all. Terrible drought conditions in Australia and poor supplies from Canada are driving prices for the crop through the roof.

This is occurring while demand is soaring as Iraq recently imported 700,000 tonnes and Algeria took in 100,000.

While prices are also being impacted by typical seasonal demand, there are plenty of buyers who put off purchases waiting for prices to moderate, which could keep prices high for awhile.

However, with that said, this is one commodity where the rug will be pulled out from under investors' feet. This looks like a short to this blogger.

Defining periods of irrational exuberance can be difficult. However, one method to do so might simply be to look at the headlines. Here are this morning's:

• Crescent Real Estate Equities to be purchased by Morgan Stanley (NYSE: MS) Real Estate
• Payless ShoeSource (NYSE: PSS) to acquire Stride Rite (NYSE: SRR)
  
• Dow Jones & Co. (NYSE: DJ) controlling shareholders, the Bancroft family, meeting to review News Corp (NYSE: NWS) offer
• Sallie Mae making management changes for its take-private transaction
• Alcan Inc. (NYSE: AL) rejects Alcoa Inc.'s (NYSE: AA) $27 billion offer as inadequate
• MGM Mirage (NYSE: MGM) approach by Kirk Kerkorian's Tracinda Corp requires delicate strategy.

The headlines are not too different from the 1980's LBO boom when virtually every headline was associated with a hostile buyout of some sort. Are we approaching the end of the buyout binge? Most likely not. These periods can last for years.

This buyout boom has been fueled by a number of factors. The most important factor has been undervalued stocks, which, in many cases, still remains. In the post tech-telecom bubble of the 1990s, investors went into a cocoon while U.S. company management continued to grow earnings and increase returns on investment.

What will end this buyout boom? My bet is a massive bull market which pushes valuations off the radar screen of private equity.

InvestmentTools.com has some great charts on copper prices. It is not a pretty picture. Below are two charts, but you can find plenty more on their webpage.

This first chart goes back to 1990. For the most part, if this chart went back to the beginning of time, the price of Copper really never stayed above $1.60. However, since 2004, copper prices have broken through the $4.00 level.