“Stubborn opposition” to fossil fuels is standing in the way of lifting billions of people out of poverty, U.S. Energy Secretary Rick Perry told a major gathering of natural gas professionals on Tuesday.

Perry is spearheading President Donald Trump‘s goal of making the United States the dominant player in the global energy market. On Tuesday, he touted the nation’s rank as the world’s biggest natural gas producer and second biggest crude oil driller in a keynote speech at the triennial World Gas Conference in Washington, D.C.

He added, however, that some domestic and foreign forces are working against the Trump administration’s goal of promoting prosperity through energy security.

“I wish I could tell you that the entire developed world is on board with our vision. I wish I could, but I cannot,” he said. “In some quarters, at home and abroad, there is still this stubborn opposition to natural gas and other fossil fuels.”

“The opposition exists even as fossil fuels become cleaner and low-emission natural gas increases its share of total fossil production and use. These opponents flatly reject the all-of-the-above strategy, the innovation-driven strategy that’s helping us achieve energy security,” Perry told the conference.

Surging natural gas production, along with renewable energy, has indeed pushed dirtier fuels like coal out of the energy mix. Technologies designed to scrub emissions from coal-burning plants have made little commercial progress, however, and many developing nations have plans to build coal-fired facilities.

Much of the opposition to fossil fuels centers around concerns over global warming, as well as the potential impact on vulnerable communities from sea-level rise and other consequences of the world’s changing climate. Perry has publicly denied the scientific consensus that carbon dioxide emissions from human activity, including burning fossil fuels, are the primary cause of climate change.

The Trump administration has stoked outrage from some corners of the political spectrum by rolling back Obama-era rules and programs to mitigate the impacts of climate change, including regulating emissions from power plants. Trump also withdrew the United States from the Paris climate agreement, making it the only nation that is not in the pact to prevent global temperatures from rising past the tipping point.

Perry noted that forecasts indicate that oil, gas, and coal will still provide 75 percent of the world’s energy by 2040.

“The answer is not to exclude oil and gas and coal from the world’s energy mix,” Perry said on Tuesday. “For the sake of energy security. For the sake of economic security. For the sake of national security. I think for the sake of environmental progress. For the sake of our fellow human beings, we must honor the right of every nation to responsibly use every fuel at its disposal.”

Perry said the Trump administration is promoting innovation in energy development and emissions control through tax cuts that incentivize investment, rather than by regulating oil and gas companies.

However, Perry and the Energy Department have recently attracted opposition from the oil, natural gas, and renewable energy industries for trying to force electric power markets to buy energy from failing coal-fired and nuclear power plants.

U.S. regulators rejected a plan that Perry pushed last year to achieve that aim. He has since put forward another proposal that would use emergency powers based on national security to require markets to buy enough power from the plants to keep them online.