The slide in oil prices may be coming too fast to provide the traditional fillip for the world economy.

Last year’s 50 percent plunge in Brent crude from its June peak prompted most economists to predict a boost to global growth as it bolsters consumers’ spending power, echoing effects from declines in the 1980s and 1990s. Now that the fall has extended another 21 percent barely two weeks into 2015, it risks not being as positive as some first imagined.

A disorderly drop in energy and commodity prices was the first item highlighted last month in a report on the ten things that could go wrong in 2015 by Rob Carnell, chief international economist at ING Groep NV in London.

“What at first seemed to be a good news story for 2015 has rapidly shown that whilst a little of what you want is good for you, you can definitely have too much of a good thing,” wrote Carnell, who formerly worked for the U.K. Treasury.

One reason both for oil’s decline and why it may not be a strong a lift for global growth as it once was is the U.S.’s rise as an energy producer.

That means the fuel’s fall may be so quick that it will result in the postponing or cancellation of energy investment projects that brake the economy, according to Carnell.

Temporary Windfall

U.S. households may see their windfall from lower oil prices as temporary and hold back from spending all of it, which would fail to “offset the substantial decline in investment in energy production that seems likely to follow,” Carnell said in the report. “In time, such negative effects may be subsumed by stronger consumer spending and non-energy investment, but for 2015 it may not be so clear.”

JPMorgan Chase & Co. economist Robert Mellman is also questioning how oil impacts economies these days even as he and colleagues estimate it should mean international gross domestic product will be 0.5 percent higher than otherwise.

Oil’s fall and the dollar’s recent rise risk combining to slow inflation, which typically shifts income from companies to households, according to New York-based Mellman.

“Lower inflation tends to reduce growth of nominal GDP and corporate revenues relative to growth of labor and other costs,” he said in a Jan. 9 report. “The result is a squeeze on profit margins,” particularly for trade-sensitive industries such as manufacturing that are affected by dollar appreciation.

Profit Forecasts

The pinch is already being felt. Forecasts for first- quarter profits in the Standard & Poor’s 500 Index have fallen by 6.4 percentage points from three months ago, the biggest decrease since 2009, according to more than 6,000 analyst estimates compiled by Bloomberg News yesterday.

That may mean that the shift in income to consumers from companies is too sharp and ends up hurting the U.S., reducing its ability to lift demand elsewhere, according to JPMorgan.

JPMorgan economists already estimate that profits from domestic operations fell last quarter and are likely to do so again in the first three months of this year. Import volumes also cooled in the second half of 2014.

Meantime, Bank of America Corp. economist Emanuella Enenajor said Jan. 9 that if oil averages $50 a barrel this year, energy sector capital expenditure could plunge 40 percent in the U.S. Business confidence could also take a hit from fears of disinflation and the cheaper oil becomes the more consumers may save of the windfall.

“It’s likely that the incremental benefit to the economy diminishes as the oil price continues to fall,” she said.

Crude’s drop also risks imposing falling prices on more economies. According to an Oxford Economics Ltd., oil at $50 a barrel would mean negative inflation in 18 countries this year rather than just seven were it at $70.

To be sure, UBS AG economist Maury Harris yesterday noted that the oil and gas extraction sector still accounts for less than 2 percent of U.S. gross domestic product on a nominal basis and that the oil and natural industry is responsible for just 0.4 percent of non-farm payrolls. He still expects the U.S. to grow 3.1 percent this year.

While JPMorgan says similar rotations in income in 1986 and 1998 mean global growth should still do well, they note such expectations are tempered by the fact that there is less room this time for central banks to ease monetary policy in concert with oil’s drop.