Nobel Prize-winning economist and Yale professor Robert Shiller said in a recent CNBC interview that the long expansion in the economy, housing and stock markets, combined with low interest rates, likely means the U.S. is headed for a recession in the near future.

“SHILLER: Remember, we’re trying to predict human behavior, and humans thrive on surprising each other. Things like the election of Donald Trump; nobody thought that would happen back in 2015, but here it is, we’ve got him.”

“Unlike a weather man who can go out a few days, economists can go out months,” Shiller said. “But after about a year or two (projections) get iffy.

“We spend about a third of our time in recessions, so the probability going out 18 months must be something like that, but I think a little bit higher, maybe even half, given the situation. But there are so many factors that one can bring in, and I’m not confident in my ability to predict these things like I’m not confident in anybody else.”

As far as the biggest risks, Shiller first mentioned the housing market.

“The nominal home prices, referring to the S&P corelogic Case-Shiller index that I’ve been talking about, is essentially at a record high if you don’t correct for inflation,” he said. “If you do correct for inflation, it’s still really high. It’s gone up since 2012 at a good pace. I count it as the third-largest expansion of home prices since 1890.”

Robert Shiller recession

Robert Shiller recession

Next Shiller listed the longest bull market on record, followed by the lowest interest rates ever and a record expansion.

“Late last year we got a lot of attention in the news media to the idea that we’re in the longest bull market ever,” he said. “We’ve had the longest period of zero interest rates — though they’re not quite zero, they’re still on the low side. According to The National Bureau of Economic Research, we will have set a record for the length of expansion if there isn’t a recession by June of this year.

“So all of those things together suggest to me that a lot of people are thinking that this is getting late in the stages of a boom. And if history repeats, we’re in for a good chance of another recession.”

Ultimately, Shiller said, recessions are tough to predict until they’re upon you.

“Remember, we’re trying to predict human behavior, and humans thrive on surprising each other,” he said. “Things like the election of Donald Trump, nobody thought that would happen back in 2015. But here it is, we’ve got him. The same types of things can happen again. Just like wildfires in California appeared — we had a really bad year on that. That’s just another example of big surprises throughout history. But the problem is we tend to magnify them. We try to read into the California wildfires, for example, more than is justified.

“The only thing that hasn’t hurt us but in principle could, is the polarization around President Trump and the strong disagreements. The hearings that we’re having now, depending on your viewpoint, are either proving that he’s a criminal, or it’s a vindictive conspiracy against a good man. But it hasn’t affected the economy. And you know, I don’t think that it’s easy to piece out exactly why. So it may depend on how these hearings end. I’m reminded of the Army-McCarthy hearings, when Senator Joe McCarthy held hearings that were on television. They were the first really big, extravaganza hearings that everybody watched, and public opinion turned based on those hearings.”

So what exactly happened to the stock market after the McCarthy hearings?

“It boomed. It was great,” Shiller said. “The end of the Army-McCarthy hearings discredited those hearings. McCarthy ended up retreating because he didn’t look good. The questions is how these hearings now that we’ve had for President Trump, how do they ultimately affect public opinion? And I don’t know the answer. These things are hard to predict.”

Click here to watch the interview in full.