Prince William’s dad — also known as Charles, the future king of England — knows a bit about taking verbal punches.

Promoting sustainable farming and green living has been one of his life’s missions. But because he’s a royal with easy access to carbon-hogging jets, a handful of estates, flotillas of attendants and all sorts of resource-gobbling goodies, his oft-praised crusade tends to get lampooned with some frequency.

“I have been venturing into extremely dangerous territory by speaking about the future of food,” the Prince of Wales told an audience Wednesday at Georgetown University, evoking an image that could just as easily apply to his efforts to promote reducing dependence on fossil fuels. “I have the scars to prove it!”

But, for all the grief he gets, Charles clearly loves the subject, and he held forth for more than 40 minutes, delivering a dry, sobering and substantive message of impending worldwide crisis. And his remarks, once known for being radical, were delivered to a Washington audience on the day when Republicans and Democrats agreed that agri-business subsidies should be cut. Indeed, just five days after his son’s international blockbuster of a wedding to Kate Middleton, Charles seemed relieved to return to deriding agriculture’s “umbilical dependency on oil” and warning that humans “are pushing nature’s life-support system too far.”

“It certainly makes a change from making embarrassing speeches about my eldest son during wedding receptions,” he told the audience at the Future of Food conference, organized by Washington Post Live, a unit of this newspaper that holds conferences and events.

Charles’s keynote address was delivered on the second day of a three-day trip to Washington that included a stop Tuesday at Common Good City Farm, an urban farm and educational center in LeDroit Park, as well as a planned sit-down Wednesday afternoon with President Obama and a visit with Supreme Court Justice Stephen G. Breyer, whose wife, Joanna Freda Hare, is the daughter of a British noble, the late John Hare, 1st Viscount Blakenham. As Charles arrived at Georgetown’s Healy Hall, a British reporter called out a question about what the prince would discuss with the president. “Ah!” Charles said cryptically, smiling and pointing a finger in the air before moving on.

Charles was greeted by dozens of students who braved cool weather and rain to catch a glimpse of him as he rolled up to the ancient hall in a seven-car motorcade. Charles chatted briefly with some of them before entering the hall, complimenting Dominick Fiorentino, a 19-year-old business major from New York, on the British flags he was waving. “I think he’s using his position to spread a message about sustainable food,” Kevin Rafferty, a 19-year-old business major from Newtown Square, Pa., said after exchanging a few words with the prince. “I respect that.”

In parts of the blogosphere, Charles’s reception has been much frostier. Phelim McAleer, an Irish journalist and filmmaker, was getting prominent play on right-leaning blogs and YouTube with his 2-minute-14-second film “Prince Charles – Hypocrite.” It starts with a clip of Charles saying, “We are making it cool to use less stuff.” That’s followed by a rollout of images — accompanied by a Bach minuet — of vast estates. (There’s no Airbus this time. Charles flew to Washington in a private jet owned by Texas billionaire Joe Allbritton.) “Sustainability is an awful concept,” McAleer said in an interview from his Los Angeles home. “It’s rich, white people telling mostly brown and black people that they need to stay poor.”

One of the main themes of the Georgetown conference was finding ways to feed the poor that uses sustainable agriculture. The prince sought to promote methods that would not deplete soils, overtax water supplies or rely on the nitrogen fertilizers so often blamed for environmental degradation.

“For every pound of beef produced in the industrial system, it takes 2,000 gallons of water,” he told a near-capacity audience inside the ornate Gaston Hall auditorium, which is on an upper floor of Healy Hall. “That is a lot of water, and there is plenty of evidence that the Earth cannot keep up with the demand.”

Charles cited his efforts to farm “as sustainably as possible” in England. He said there is “plenty of current evidence that adopting an approach which mirrors the miraculous ingenuity of nature can produce surprisingly high yields of a wide range of vegetables, arable crops, beef, lamb and milk.”

“And yet we are told ceaselessly — ceaselessly! — that sustainable or organic agriculture cannot feed the world.” The prince argued that we need a “more honest form of accounting” that takes into account the health problems associated with fertilizers and other products used to boost production.

He called for a new kind of “Washington consensus” about sustainable food production, invoking a term used for the controversial neo-liberal, market-friendly policies frequently associated with international aid and lending organizations. Charles’s Washington consensus would seek to balance the needs for markets and a private sector but “recognize the real opportunities and trade-offs needed to build a food system that enhances and ensures the maintenance of social, economic and environmental capital.”

He ended his remarks by laying a heavy measure of responsibility for the future of food on the United States. He quoted George Washington, saying, “Raise a standard to which the wise and honest can repair; the rest is in the hands of God.” Then, he added a coda: “And, indeed, as so often in the past, in the hands of your great country, the United States of America.”

Back home, Charles is famous for operating his Aston Martin on a clean-running biofuel made from surplus wine. Citing “security-related” issues, a British Embassy spokesman declined to say whether any of the vehicles in Charles’s motorcade — which included a Chevrolet Suburban, a Mercedes-Benz sport-utility vehicle, a Jaguar, a Chrysler 300 and a Cadillac — run on electricity or are hybrids. Some of the vehicles are operated by the U.S. State Department, the spokesman said.

As Charles visited with dignitaries inside Healy Hall, the motorcade and its drivers waited at the front door. An SUV with diplomatic plates was making a bit of noise. Its motor was running.