BlackRock, the world's largest asset manager, has become a signatory to Climate Action 100+, joining more than 370 other investors, including AustralianSuper, amid a heightening global focus on climate risks.

The decision follows criticism that BlackRock wasn't as "green" as it led investors to believe, and a warning by Emily Chew, chairwoman of the steering committee of Climate Action 100+, that big investors would intensify their activism on climate change in 2020, including voting against directors on climate-related shareholder resolutions.

In a statement, BlackRock said the decision to join the group was "a natural progression" of work done within the investment firm to date.

"We believe evidence of the impact of climate risk on investment portfolios is building rapidly and we are accelerating our engagement with companies on this critical issue.”

With the addition of BlackRock, and the $US6.8 trillion ($10 trillion) in assets it manages, investors with more than $US41 trillion in assets under management have signed on to the Climate Action 100+ initiative.