U.S. stocks are lower on Wednesday afternoon, with the Dow Jones Industrial Average (DJINDICES:^DJI) and the S&P 500 (SNPINDEX:^GSPC) down 0.39% and 0.58%, respectively, at 2 p.m ET. Meanwhile, in the run-up to OPEC's key meeting on Friday, oil prices are near six-year lows today.

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Daniel Yergin, an energy industry expert and the author of The Prize: The Epic Quest for Oil, Money, and Power, penned a downbeat comment published on CNBC's website yesterday titled "The party is over for oil," in which he writes:

When oil prices started taking off in 2004, it was part of the same "commodity supercycle" that sent prices of so many other commodities spiraling up. Oil stayed at the party longer than anyone else but now, the party is over... Oil's collapse does mark the end of the commodity supercycle...

[O]il's turmoil will continue. For new petroleum supplies are likely to come into the market in 2016.

"... the hard times are really now at hand."
Mr. Yergin had earlier described oil producers' predicament in an August interview:

I think companies are now expecting that prices are going to be in a lower range, longer. This is definitely not a V-shaped recovery. And it's going to be more of a stretched-out U, with the right-hand side never quite getting back to the level of the left... There was a period of renewed optimism but I think the hard times are really now at hand.

I wonder whether, on top of a difficult pricing environment, oil producers won't face a less hospitable environment in the capital markets in the years to come.

As the COP21 Paris Climate Conference kicked off this week, the Financial Times reported this morning that campaigners are announcing that at least 500 insurers, banks and investment funds controlling $3.4 trillion in assets have pledged to avoid or reduce fossil fuel industry holdings.

They include German insurer Allianz, which has pledged that it would sell its investments in companies involved in the coal industry to the tune of 4 billion euros ($4.3 billion).

Coal companies are first in the line of fire because they are the dirtiest energy source. While the $3.4 trillion figure may overstate the extent of investors' retreat -- the World Coal Association says it includes many institutions that already had no exposure to coal -- the speed of the uptake in the campaign is impressive. Campaigners say the equivalent figures a year ago were roughly $50 billion in assets under 181 institutions.

The $890 billion "clean" fund
Presumably, one of the new institutions that has taken up the pledge is Norway's $890 billion Government Pension Fund Global. At the beginning of June, Norwegian lawmakers voted to force the world's largest sovereign wealth fund to sell those of its holdings that rely at least 30% on coal.

The decision was highly symbolic: The fund, which was established in 1990, was originally named the Government Petroleum Fund, as it was funded out of the government's petroleum revenue.

"A century from now..."
In his 2011 shareholder letter, Warren Buffett wrote that "[a] century from now... ExxonMobil will probably have delivered trillions of dollars in dividends to its owners and will also hold assets worth many more trillions."

However, I think it's reasonable to ask what degree of certainty we have that ExxonMobil will still exist 100 years from now, let alone that it will have trillions of dollars of assets.

As the world begins to shift away from fossil fuels toward clean energy sources, it should be noted that the track record of incumbent companies successfully pivoting in the face of momentous structural shifts is pretty disastrous.

(Buffett sold Berkshire Hathaway's entire $3.7 billion stake in ExxonMobil in the fourth quarter of 2014, but this was not the result of a change in his assessment of the oil supermajor's long-term prospects. He has since established a significantly larger position in refiner Phillips 66.)

I think the prospects for shares of oil and gas majors over the next five to seven years are good -- they look poised to beat the broad market. Over a 20- to 30-year time frame, however, these companies' position as "inevitable" looks less assured.

Alex Dumortier, CFA has no position in any stocks mentioned. The Motley Fool has no position in any of the stocks mentioned. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.