Major oil companies received a blow on Tuesday night after one of the main rating agencies, S&P Global Ratings, warned that it could downgrade the ratings of giants such as Exxon Mobil, Shell and Chevron in the coming weeks, due to higher risks associated with climate change, Bloomberg reports.

S&P Global Ratings’ decision comes at a time when the oil and gas industry is going through a difficult period, facing many pressures after US President Joe Biden put climate change at the center of his political agenda.

“S&P Global Ratings considers the energy transition, price volatility and low profitability to be increasing risks for oil and gas producers,” the rating agency said on Tuesday, adding that it has revised the risk assessment for the entire oil and gas industry from “intermediate “to “moderately high,” according to Agerpres.

In addition to Exxon Mobil, Shell and Chevron, S&P has overseen the ratings of oil companies Woodside Petroleum, Imperial Oil, Shell Energy North America, Canadian Natural Resources, ConocoPhillips, Total and the ratings of China’s top four oil producers China Petrochemical. Corp., China Petroleum & Chemical Corp., China National Offshore Oil Corp. and CNOOC.

If the ratings of large oil companies are lowered, their capital costs will increase, as investors will demand higher returns, which could jeopardize the start-up of new oil and gas projects. This happens while the big oil companies have problems in generating a high return on investments, but so far they have taken advantage of the fact that investors have been willing to lend money at low interest rates.

With the exception of Exxon, whose rating was downgraded in March after oil prices plummeted, major European and US oil companies did not suffer a downgrade, after 2016.

However, S&P Global Ratings warned that the oil sector faces “significant challenges and uncertainties caused by the energy transition, which could put pressure on profitability, especially on return on investment.” In the golden age of the early 2000s, large oil companies had a return on investment of over 10%, but in recent years some companies in this sector have had trouble reaching a return on investment of more than 5%.