The trustees of 14 UK pension schemes have received letters warning of imminent legal action should they fail to consider the financial risks associated with climate change.
The BP Pension Fund and Lloyds Bank pension scheme were among those contacted from lawyers at ClientEarth, which said evidence of climate-related risks was "fast stacking up".
The letters ask trustees to make a public statement outlining what steps they are taking to tackle the risks, and warn that legal action by scheme members could soon follow.
This comes after the Environmental Audit Committee (EAC) proposed mandatory reporting after finding that four of the UK's 25 largest funds do not acknowledge climate risks.
ClientEarth lawyer, Joanne Etherton, said the findings displayed a "woeful" level of understanding, and that schemes must step up action to future-proof members' pensions.
"Trustees' legal duties are not static and a court would look to the evidence available, and how their peers are responding, in determining whether they are in breach," she continued.
"In short, legal duties on climate risk are evolving. We are now putting these schemes on notice of the available evidence and setting out the standard they should be looking to meet."
New research by ClientEarth and consultancy firm Sustineri found that private pension schemes tend to lag behind sovereign wealth funds and public schemes on this issue.
It was also found that asset owners are starting to focus on long-term risks, but may still be neglecting the short and medium-term threats arising from climate change.
However, two-thirds of the asset managers studied had divestment policies for companies that have not been responsive to engagement efforts or emit high volumes of carbon.
"The combination of fiduciary duty and a focus on risk-adjusted returns over the longer-term are acting as primary drivers for action," ClientEarth said.
"Many asset owners no longer consider climate change as an 'ethical' or 'niche' concern, but increasingly recognise a material financial risk to the medium and long-term value of their funds."