Former Vice President Al Gore explained why he routinely compares the fight against global warming to the civil rights, anti-apartheid and abolitionist movements during a live SiriusXM radio town hall Thursday.

“Because what all three of those issues have in common is a group of advocates trying to bring about a morally-based change in policies that have caused tremendous harm,” Gore said when an NBC News reporter asked him about comparing his work to the civil rights and gay rights movement.

“In all three of those cases, there has been ferocious resistance to the change being advocated, and in all three of those cases, there have been advocates of change that were tempted to despair,” Gore said.

Gore said all three cases eventually “boiled down to a pretty simple choice between what’s right and what’s wrong.” Gore went on to quote Nelson Mandela about the anti-apartheid movement in 1990s South Africa.

Gore was recently criticized for comparing his crusade against global warming to the abolition of slavery, ending apartheid, and the civil rights, women’s rights and gay rights movements — something he’s done many times in the past.

The global warming fight is “in the tradition of all the great moral causes that have improved the circumstances of humanity throughout our history,” Gore said in Australia in July, according to Climate Depot.

“The abolition of slavery, woman’s suffrage and women’s rights, the civil rights movement and the anti-apartheid movement in South Africa, the movement to stop the toxic phase of nuclear arms race and more recently the gay rights movement, Gore said.

Gore made similar comparisons during a 2013 interview with The Washington Post. In 2011, Gore compared winning “the conversation” on global warming to building support for civil rights.

This time, black conservative activists criticized Gore’s comparison of slavery and civil rights to the fight against global warming.

“When Al Gore, Jr. associates these moral movements of history with one grounded in questionable data, he gives climate change activists unearned moral credibility they haven’t earned and don’t deserve,” said Horace Cooper, co-chairman of the Project 21 initiative with the group Conservative Black Leadership.

Horace also pointed out that Gore’s father, a former Democratic Tennessee Senator, opposed civil rights initiatives in the 1960s, though he did support the Voting Rights Act of 1965.

“Fighting people being owned as property and debased in an entrenched system enshrined in law is akin to worshiping the idea that humans can materially impact the climate?” Project 21 co-chairman Stacy Washington asked in a statement.

“He cannot be serious!” Washington said.

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This article originally appeared in The Daily Caller