Ed Yardeni, chief investment strategist at Yardeni Research Inc., has harped on the weakness of commodities over the past two years, and he is being proven right.

Major commodity indices have dropped to 13-year lows amid copious supply and weak demand. And the implications aren't pretty for the global economy, he says.

“Over the past couple of years, I have written that the commodity super-cycle wasn’t so super,” even suggesting that it might have been a bubble, he said.

"It appears that the bubble is bursting this year with negative consequences for the global economy, particularly for commodity-producing companies and countries," Yardeni writes in a commentary provided to Newsmax Finance.

"That certainly explains why the global economy is mired in secular stagnation."

The U.S. economy grew a mediocre 2.3 percent in the second quarter, while the eurozone economy expanded only 1.3 percent and Japan contracted 1.6 percent.

So does this mean a global recession?

"It all depends on whether the U.S. economy can decouple from the global morass and provide enough growth to offset the weakness in China, Japan, and the eurozone," Yardeni explains. "In the past when bubbles burst, recessions tended to follow. So history isn’t on our side."

Mohamed El-Erian, chief economic adviser at Allianz, is concerned about the global picture too, especially the troubled economies and financial markets in developing nations.

"What we're seeing is a classic overshoot that starts in the emerging markets world, and it starts spreading," he told CNBC. "What that causes is heightened risk aversion."

In China, the government devalued the yuan last week—it has since dropped 3 percent—and the Shanghai Stock Exchange Index has plunged 29 percent since June 12. The government reported second-quarter economic growth at 7 percent, but economists say the true figure may be 3 to 5 percent.

Investors will dump their holdings in emerging markets first, "but at the end is the U.S. equity market," El-Erian said.

With the bull market for U.S. stocks now almost 6 ½ years old, many analysts say equites are ripe for a correction. The S&P 500 hasn't declined 10 percent since October 2011. It currently stands just 4 percent below its record high.

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