Whenever he launched an ideological crusade, he did so zealously — even if, as in the case of ecosocialism, its very definition and the collateral demand for an appealing alternative to capitalism were not self-evident.

Under ecosocialist theory, income would be guaranteed, most property and means of production would be commonly owned, and the abolition of capitalism, globalism and imperialism would unleash environmentalists to vastly curtail industrialization and development whose pollution would otherwise cause catastrophic global warming.

“Capitalist production, in its endless search for profit, seeks to turn everything into a commodity,” Dr. Kovel wrote in 2007 on the socialist website Climate and Capitalism. “It is plain that production will have to shift from being dominated by exchange — the path of the commodity — to that which is for use, that is for the direct meeting of human needs.”

Joel Stephen Kovel was born on Aug. 27, 1936, in Brooklyn to Louis and Rose (Farber) Kovel. His father was an accountant and the namesake of the Kovel Rule, a legal doctrine that extended the lawyer-client confidentiality privilege to other professionals and experts. It arose when a federal appeals court voided the elder Mr. Kovel’s one-year sentence for contempt after he had refused to answer questions about a client in a case.

After graduating from Baldwin High School in Baldwin, N.Y., Joel received a bachelor’s from Yale in 1957 and a medical degree from Columbia University College of Physicians and Surgeons. While in medical school, he was first exposed to extreme poverty during field study in Suriname. He trained at Downstate Psychoanalytic Institute in Brooklyn.

In addition to his wife, a filmmaker, Mr. Kovel is survived by two children, Jonathan Kovel and Erin Fitzsimmons, from his marriage to Virginia Ryan, which ended in divorce; a daughter, Molly Kovel, from his marriage to Ms. Halleck; her sons, Ezra, Peter and Tovey Halleck, from an earlier marriage; his brother, Alex; and nine grandchildren.