In an interview with the BBC's Chris Fox, Microsoft president Brad Smith admitted that the plan was a "moonshot" - a very big idea with no guaranteed outcome or profitability - for the company.

He stressed there was simultaneously a sense of urgency and a need to take the time to do the job properly.

He also said that the tools required don't entirely exist yet.

Mr Smith talked about tree planting, and direct air capture - a way of removing carbon from the air and returning it to the soil - as examples of available options.

"Ultimately we need better technology," he said.

But don't expect Microsoft to roll up its sleeves: "That's not a business we will ever be in but it's a business we want to benefit from," he added, announcing a $1bn Climate Innovation Fund, established with the intention of helping others develop in this space.

Microsoft makes 'carbon negative' pledge

He expects support from the wider tech sector, he said, "because it's a sector that's doing well, it can afford to make these investments and it should."

But historically, isn't it also one of the worst offenders?

CES in Las Vegas, the huge consumer tech show, has just ended. It was attended by 180,000 people most of whom probably flew there, to look at mountains of plastic devices clamouring to be the Next Big Thing.

From gas-guzzling cars and power-hungry data centres to difficult-to-recycle devices and the constant consumer push to upgrade to new shiny plastic gadgets - the tech sector's green credentials are not exactly a blueprint for environmental friendliness despite much-publicised occasional projects.

There was no immediate announcement from fellow tech giants about any collaborations with Microsoft, or indeed similar initiatives of their own - but the aim is ahead of the current ambitions of many, including Facebook, Google and Apple, which have not (yet) made a "carbon negative" commitment.

That said, software-maker Intuit has pledged to be carbon negative by 2030, and Jeff Bezos announced in September 2019 that Amazon would be carbon neutral by 2040.