One hundred and thirty-one trillion dollars. This, according to the International Renewable Energy Agency’s (Irena), is the total investment needed through to 2050 to keep global warming to a civilisation-rescuing 1.5°C above pre-industrial temperatures.

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To achieve this, spending on renewables must rise by 30% over currently planned levels to an extraordinary $4.4trn a year to mid-century, Irena calculates.

The silverest of linings to a brutal global pandemic is that money of this magnitude is already being marshalled by international governments to revive Covid-stricken economies. However, deploying this massive capital shift will need to be fast-tracked to get through “a window that’s closing fast”, as Irena chief Antonio La Camera has starkly stated.

A radical redirection of finance is needed, given that governments around the globe underwrote the fossil-fuel sector with $233bn in Covid recovery stimulus funding last year while channelling only $146bn to renewables.

Business-as-usual, as UN secretary-general António Guterres proclaimed in December in a speech timed to coincide with a report on G20 nations’ energy transition, would be a continuation of the “suicidal war on nature” being waged by humanity today.

Courage rightly continues to be taken from the fact that the smart money remains firmly placed on wind, solar and the other technologies required for a sustainable future.

Investors in renewables, as a new report from the International Energy Agency has underlined, are winning hands down over those backing fossils, with clean-energy power portfolios providing a 367% greater total return over the past decade, pointing to a “broader structural trend” away from oil, gas and coal.

Yet here too, the tell-tale “large disparities” persist between governments’ energy transition ambitions and their continued buttressing of the terminally declining petroleum sector.

Globally, the renewables build-out continues to boom. Last year, a record 100GW of new wind power projects were set turning and almost 200GW of solar wired in, with triple-digit-gigawatt additions of the two technologies expected in 2021.

Big Oil’s evolving budgetary commitments to 2050 will be central to the gear-up to hit the 27.7TW of renewables that Irena says will be needed — covering 90% of all electricity demand, with power accounting for more than 50% of final energy consumption, up from 21% now.

But ultimately, it will be the actions taken by the world’s two biggest polluters, China and the US, that will determine the future.

Here, judgement must for now be withheld. Beijing’s strides toward carbon neutrality so far, it is widely agreed, have been “baby steps”, but a clear trajectory to its 2030 target could change attitudes.

And, in Washington DC, President Joe Biden’s move to rejoin the Paris Agreement and his vow to invest $2trn in American clean-energy production and supply-chain development during his four-year term will be a down payment on realising longer-range global climate commitments.

“This is an epic policy test,” said Guterres. “But ultimately this is a moral test. It is time to flick the ‘green switch’. We have a chance to not simply reset the world economy but to transform it.”

Hopefully, his words will one day be looked back on as a turning point.