While the S&P/Case-Shiller home price index rose more than 12 percent year-on-year for the second month in a row in June, the good times may not last, says Yale economist Robert Shiller, co-founder of the index.

For now things look fine, he told CNBC. "Obviously we're in a housing recovery, at least for the short term. Housing is a market with momentum, and right now, the momentum is up."

But what about the future?

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"Especially in the single-family realm, I think that there is a chance that there is weakening," Shiller noted. "There's all this fear over [Federal Reserve] tapering that's a cloud over the housing market now."

The housing market has turned extremely speculative, Shiller explained. "It's just a rollercoaster, that's what these markets have become." The market is "driven by irrational exuberance, and that can just suddenly change," he said.

So the current rally may be of limited importance beyond the short term. "For a long-term buyer the fact that they [home prices] are going up now doesn't mean a whole lot about where they're going to be when you finally sell," Shiller said.

While the 12.1 percent gain in Shiller's index for the year through June represented a decline from 12.2 percent in May, many analysts say the housing market remains on solid ground.

The "rate of growth of home prices is certainly slowing, but we're still posting respectable year-over-year increases," Brian Jones, a senior U.S. economist at Societe Generale, told Bloomberg.

"Housing's in good shape. We're always going to keep one eye on mortgage rates to see if there is an appreciable impact going forward."

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