"I think around 2004, certainly there were black nominees -- like Don Cheadle, Morgan Freeman. And all of a sudden, you feel like we're moving in the wrong direction," Clooney said. "There were nominations left off the table. There were four films this year: Creed could have gotten nominations; Concussion could have gotten Will Smith a nomination; Idris Elba could have been nominated for Beasts of No Nation; and Straight Outta Compton could have been nominated. And certainly last year, with Selma director Ava DuVernay -- I think that it's just ridiculous not to nominate her."
Clooney pointed to opportunity as a possible root factor in the issue.
"I don't think it's a problem of who you're picking as much as it is: How many options are available to minorities in film, particularly in quality films?" he wrote.
The actor also used the moment to acknowledge gender inequality in film, noting that "a woman over 40 has a very difficult time being a lead in a movie," and praising Jennifer Lawrence and Patricia Arquette for making "the loud pronouncement about wage disparity."
The Academy's first black president, Cheryl Boone Isaacs, issued a statement in which she called for "big changes." ET's Nischelle Turner asked Isaacs about the issue of diversity at the Oscars moments after the nominees were announced.
"It's disappointing," she said at the time.
Some were so disappointed that there has been a call for Chris Rock to step away from his hosting duties, but according to The Hollywood Reporter executive editor Matthew Belloni, Rock is more likely to uphold his agreement with the Academy.
"The widespread consensus in Hollywood is that Chris Rock should not step down," Belloni told ET. "There is so much opportunity for him to make a statement about this year's Oscars."
Jada Pinkett Smith, who is boycotting the Oscars, supported Rock hosting the show via Facebook on Monday, saying, "I can't think of a better man to do the job at hand this year than you, my friend."
Emmy-nominated actress Niecy Nash weighed in on Smith's proposed boycott at the Critics' Choice Awards.
"I don't know if avoiding it altogether is going to help, but I just think we have to continue to move forward," Nash told ET. "We have this awareness and this spotlight -- we've got to look at other work. There's other work out there that I think was missed. We've just got to do better."
Smith later applauded the Academy for taking swift action on Tuesday, especially praising Isaacs.
"I would like to express my gratitude to the Academy, specifically Cheryl Boone Isaacs, for such a quick response in regard to the issue at hand," she tweeted. "I look forward to the future."