William Ruckelshaus, who served as the Administrator of the U.S. Environmental Protection Agency under Presidents Richard Nixon and Ronald Reagan, and William Reilly, who manned the same helm for President George H. W. Bush, issued a statement denouncing GOP nominee Donald Trump’s “profound ignorance of science.”

“That Trump would call climate change a hoax – the singular health and environmental threat to the world today – flies in the face of overwhelming international science and the public conviction,” they said. “The young people in this country deserve far better.”

“He hasn’t a clue about Republicans’ historic contributions to science-driven environmental policy,” the former Administrators wrote, highlighting the environmental achievements of their former bosses, including Reagan’s international leadership in addressing the depletion of the ozone, which led to the highly praised Montreal Protocol. Earlier this year, Trump mocked the protocol, which phased out of harmful chlorofluorocarbons commonly found in household products such as hairspray. “We Republicans should be shocked, outraged even, at the prospect that all this progress, this legacy will be repudiated and rolled back by Donald Trump.”

Both Ruckelshaus and Reilly have been strong advocates for continued Republican leadership on environmental issues. Earlier this year, former New Jersey Gov. Christine Todd Whitman, who served as President George W. Bush’s first EPA Administrator, likewise called into question Trump’s climate change positioning.