This is a problem

How much more can corporate earnings grow?

If you look at the recent history, you can see clearly that growth has plateaued. And it's a theme that Wells Capital Management's Jim Paulsen warns "could become problematic" for stock market investors.

"While this economic cycle will most likely last several more years, aspects of the recovery are already getting old," Paulsen writes. "Chief among these is a rapidly maturing earnings cycle. [The chart] shows the trailing 12-month earnings per share for the S&P 500 Index. Corporate profitability recovered smartly during the early years of this recovery, but similar to past cycles, has slowed in recent years. In the last three years, S&P 500 earnings per share have risen only slightly more than 5% per annum and less than 4% annually after inflation. Indeed, total U.S. corporate profits (from the National Income & Product Accounts) have been essentially unchanged for the last three years!"

This isn't exactly news. But analysts are becoming increasingly vocal about this. After all, earnings and expectations for earnings growth are the most important drivers of stock prices.

On Friday, Deutsche Bank's David Bianco pointed out that if you consider GAAP earnings - that's the earnings figure that doesn't exclude adjustments that companies make to smooth out the numbers - earnings are actually declining.

"The S&P avoided down EPS in 1H15, up ~2% y/y on non-GAAP EPS, but the GAAP EPS declined by 13% y/y," Bianco added. "We have always argued that the best EPS measure lies somewhere between GAAP and non-GAAP EPS."

This might come as a surprise to everyone as they watch jobs grow, unemployment come down, auto sales surge, home prices rally, and stock prices sit near record levels. But when everything's great, it's reasonable to be concerned that we're near the top. Indeed, Goldman Sachs' David Kostin was "surprised" to hear clients asking about the prospect for a US recession in 2016.

"It's amazing how forgiving the general commentary has been on profits and even the broad economy," Bianco said in an email to Business Insider. "Many seem to celebrate the absence of a recession. The labor market continues to tighten and thus I expect the Fed to hike, but other than some bright spots like auto and housing, growth is extremely weak with underlying drivers like productivity and investment disturbingly poor and S&P profits are not growing."

Like Paulsen said, this "could become problematic," especially since the stock market is trading at historically high valuations.

"Earnings performance is well past its best for this recovery and investors need to consider whether earnings growth will prove sufficient to support current stock market valuations," Paulsen wrote. "The rapidly aging earnings cycle is perhaps best illustrated by an economy nearing full employment with corporate profit margins near record highs. Should global growth remain tepid and overall sales results modest, since profit margins are unlikely to rise much, earnings trends will also likely prove disappointing. Conversely, should global growth and corporate sales results accelerate, because the U.S. is nearing full employment, companies may soon face cost-push pressures and margin erosion which will likely offset improved sales results."

Paulsen and Bianco, both veteran stock market strategists, have each been dubbed "perma-bulls" at one point or another. None of what they've been saying lately has been very "perma-bullish."