WASHINGTON — The Yale economist William D. Nordhaus has spent the better part of four decades trying to persuade governments to address climate change, preferably by imposing a tax on carbon emissions.

His careful work has long since convinced most members of his own profession, and on Monday he was awarded the 2018 Nobel Memorial Prize in Economic Sciences in recognition of that achievement.

But Professor Nordhaus sadly noted that he hadn’t convinced the government of his own country.

“The policies are lagging very, very far — miles, miles, miles behind the science and what needs to be done,” Professor Nordhaus said shortly after learning of the prize. “It’s hard to be optimistic. And we’re actually going backward in the United States with the disastrous policies of the Trump administration.”

Professor Nordhaus shared the prize with Paul M. Romer, an economist at New York University whose work has demonstrated that government policy plays a critical role in fostering technological innovation.