Rocker David Gilmour auctioned 120 instruments from his massive guitar collection for a $21 million windfall that the former Pink Floyd frontman is donating to fight global warming.

Christie’s auction house hosted the auction, the largest guitar sale the seller ever held.

Gilmour’s auction haul will be donated to liberal activist group ClientEarth, a non-profit organization dedicated to environmental law, according to NBC News. On its Facebook page, ClientEarth claims that it works to “combat climate change” and also to “defend habitats and wildlife.”

After the auction, David Gilmour took to his Twitter account to tell fans about his reasoning for the donation.

“We need a civilized world that goes on for all our grandchildren and beyond in which these guitars can be played, and songs can be sung,” Gilmour tweeted on Wednesday. “The global climate crisis is the greatest challenge that humanity will ever face, and we are within a few years of the effects of global warming being irreversible.”

The global climate crisis is the greatest challenge that humanity will ever face, and we are within a few years of the effects of global warming being irreversible. (2/5) — David Gilmour (@_DavidGilmour) June 19, 2019

The choice really is that simple, and I hope that the sale of these guitars will help ClientEarth in their cause to use the law to bring about real change. (4/5) — David Gilmour (@_DavidGilmour) June 19, 2019

We need a civilised world that goes on for all our grandchildren and beyond in which these guitars can be played and songs can be sung. David (5/5) — David Gilmour (@_DavidGilmour) June 19, 2019

“One of the 126 items sold at the auction was Gilmour’s “Black Strat” guitar, which he reportedly used to record “Dark Side of the Moon.” The item was expected to sell for around $150,000, but ended up selling for almost $4 million.”

Follow Warner Todd Huston on Twitter @warnerthuston.