Media playback is unsupported on your device Media caption Valerie Rockefeller Wayne, chair of the Rockefeller Brothers Fund, spoke to the BBC about the decision

Heirs to the Rockefeller family, which made its vast fortune from oil, are to sell investments in fossil fuels and reinvest in clean energy, reports say.

The Rockefeller Brothers Fund is joining a coalition of philanthropists pledging to rid themselves of more than $50bn (£31bn) in fossil fuel assets.

The announcement was made on Monday, a day before the UN climate change summit opens on Tuesday.

Some 650 individuals and 180 institutions have joined the coalition.

It is part of a growing global initiative called Global Divest-Invest, which began on university campuses several years ago, the New York Times reports.

Pledges from pension funds, religious groups and big universities have reportedly doubled since the start of 2014.

UN summit

Rockefeller Brothers Fund director Stephen Heintz said the move to divest from fossil fuels would be in line with oil tycoon John D Rockefeller's wishes,

"We are quite convinced that if he were alive today, as an astute businessman looking out to the future, he would be moving out of fossil fuels and investing in clean, renewable energy," Mr Heintz said in a statement.

Image copyright Getty Images Image caption The last major conference on climate change, in Copenhagen in 2009, ended without results

The philanthropic organisation was founded in 1940 by the sons of John D Rockefeller. As of 31 July 2014, the fund's investment assets were worth $860m.

"There is a moral imperative to preserve a healthy planet," Valerie Rockefeller Wayne, a great-great-granddaughter of Mr Rockefeller and a trustee of the fund, is quoted by the Washington Post as saying.

A climate change summit is due to start on Tuesday at the UN headquarters in New York, with 125 heads of state and government members expected to attend.

It is the first such gathering since the unsuccessful climate conference in Copenhagen in 2009.

At the scene: Matt McGrath, Environment Correspondent, BBC News

The event held to launch the Rockefellers' news was more revivalist meeting than press conference. There was whooping, cheering, hollering and stamping of feet.

Archbishop Desmond Tutu appeared by video and told the assembly that the move was "a tipping point of transition to a new energy economy that was just and equitable".

Rockefeller Brothers Fund director Stephen Heintz said dryly that "everyone noted the irony" that a foundation built on oil wealth would now be leading the charge out of fossil fuel.

Actor Mark Ruffalo, who also signed the pledge, told the conference: "These are not silly people, these are people who know how to deal with money."

They recognised that clean energy was "the future", he said - prompting more whooping, cheering and stamping of feet.

UN Secretary General Ban Ki-moon hopes leaders can make progress on a universal climate agreement to be signed by all nations at the end of 2015.

On Sunday, hundreds of thousands of marchers took to the streets in more than 2,000 locations worldwide, demanding urgent action on climate change and calling for curbs on carbon emissions.

Business leaders, environmentalists and celebrities also joined the demonstrations, which were organised by The People's Climate March.