An auction of David Gilmour's guitars has raised $US21.5 million ($A31.1 million) to combat climate change.

Christie's auction house says it raised the money after selling off more than 120 guitars owned by the Pink Floyd guitarist, singer and songwriter.

Proceeds went to ClientEarth, a nonprofit fighting climate change.

The items included guitars by Fender, Rickenbacker, Ovation, Gibson, CF Martin and Gretsch, along with guitar cases, a banjo and amps.

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A black Stratocaster - dubbed the "Black Strat" - was the top item and was snatched up for $US3.98 million ($A5.8 million), a new world record for a guitar at auction.

Gilmour, 73, said he hoped future generations could play the instruments.

"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," he tweeted.