NEW YORK ( TheStreet) -- Few expected that a shale drilling boom could push natural gas prices to near decade lows at $2 per million BTU's. But even fewer anticipated its quick 50%-plus rise from 2012 lows and investors now need to prepare for an impact on industrials and agricultural stocks, according to a Monday note from Citigroup. Rising natural gas prices above $3.25 on the heels of a near 20% jump in the commodity's prices in September may provide a dent to the fourth quarter earnings of agricultural and industrials giants like CF Industries ( CF), Eastman Chemical ( EMN), Dow Chemicals ( DOW), LyondellBasell ( LYB) and Agrium ( AGU), according to Citigroup. The sudden surge in commodity prices may signal and end to decade low natural gas prices hit in early 2012 on a glut of supply from the explosion of shale drilling -- cutting at the margins of producers who use gas as a key input - and denting fourth quarter earnings by between roughly 5% and 10%, Citigroup calculates. Current natural prices at $3.35 are roughly 25% above Citigroup's year-end forecast for the commodity and in-line with 2013 estimates, causing analyst P.J. Juvekar to reduce fourth quarter earnings estimates and forecast that the tailwind on operating margins may be closer to an end than some expect. "A sustained increase in natural gas prices could be a risk to earnings in 4Q, and possibly beyond," writes Juvekar, in a Monday note to clients. "The companies most impacted in our universe are nitrogen fertilizer and commodity chemical companies, in particular CF, EMN, DOW, and LYB," he adds, in a note cutting the fourth quarter EPS estimates of nitrogen producers like CF Industries and Agrium by 11% and by 5% on ethylene producers like Dow Chemical and LyondellBasell. In spite of the recent commodity price rise, many notable industrials investors continue to preach the positive earnings impact of low gas prices and vast U.S. shale supplies. Earlier in October, hedge fund giant Jana Partners said it is counting sustained low natural gas prices and the benefits of a shale drilling boom to be a key piece of its $500 million-plus investment in Calgary-based Agrium, and its push for agricultural conglomerate to unlock share value by splitting its retail business from a much larger wholesale business. Jana Partners calculates that the benefits of low natural gas prices and a breakup of Agrium could unlock a $50 a share upside in the company.