Every year, Google leaders send out a quirky shareholder letter riffing on the company’s progress and outlook. This year’s missive, arriving in the midst of heated debates on technology’s role in society, struck a decidedly somber note.

Sergey Brin, president of Google parent Alphabet, said on Friday that technology companies must take greater responsibility for the social impact of their work, his first comments following a year of heightened global awareness about misuse of digital services.

Brin delivered the message, which warned specifically of the dangers of Artificial Intelligence, through Alphabet's annual shareholder letter, which he signed for the first time since 2014 instead of Chief Executive Larry Page.

"We’re in an era of great inspiration and possibility, but with this opportunity comes the need for tremendous thoughtfulness and responsibility as technology is deeply and irrevocably interwoven into our societies," Brin wrote after quoting from Charles Dickens’ novel "A Tale of Two Cities" about the "the best of times" and "the worst of times."

Alphabet's primary unit, Google, has become a top target in Silicon Valley for regulators, authorities and critics in advertising and media.

It has drawn global scrutiny for its dominance in online search advertising, its policies around user privacy and its role in helping politically consequential misinformation spread online.