The former governor of the Bank of England, Mark Carney, has added his voice to calls for industrialised nations to invest in a greener economic recovery from the Covid-19 crisis.

He said that the pandemic was "a terrible situation, but there was also a big opportunity" at the end of it.

"We have a crisis with climate change which will involve every country in the world and from which we can't self-isolate," he added.

He recommended regulatory policies that would push economies more quickly towards greener growth - and a more sustainable future - citing the UK's plan to phase out petrol and diesel cars by 2035.

Governments, he added, should also take the opportunity to invest in wind and solar power to accelerate the transition to greener energy.

Many experts have pointed out that one of the few upsides of the pandemic has been lockdown's positive environmental impact. Air pollution has plummeted. Carbon emissions are set to fall by 5.5%.

This isn't enough to tackle the climate crisis by itself, they argue. But the question now is not when will life return to normal but what "normal" do we want to return to?

For many, the answer lies in a Green New Deal, aimed at achieving system change and tackling both inequality and the climate crisis. The term can mean slightly different things in different contexts, but the core ideas remain the same.

Firstly, it means only getting energy from renewable sources in the future, retrofitting buildings to improve energy efficiency.

Secondly, it means protecting and expanding ecosystems, such as forests, that take carbon dioxide out of the air.

Thirdly, it means ending dependence on businesses that pollute the environment.

The massive social changes required to make these things happen would create hundreds of thousands of new "climate jobs" - such as those in renewable energy - which would actively help bring emissions down.

In the UK, activist Jonathan Neale has even proposed the creation of a National Climate Service - an organisation like the NHS, funded by the government, which would employ people to make this a reality

But critics are numerous. Such changes are impossible, they say. Too fast. Too expensive. Too big. After the coronavirus, we simply need to get back to business as quickly as possible.

No, argue its critics. These ideas are utopianImpossibly perfect. The term comes from an ancient Greek phrase meaning "no-place" invented by Henry VIII's chancellor, Sir Thomas More, in 1516, as the name of an imaginary, ideal island., a pipe dream. They would put millions out of work, destroy prosperity, and cost too much. The priority after the latest coronavirus has to be getting businesses and the economy back to work, as quickly as possible. Unfortunately, the climate may even have to become less of a priority to achieve this.

Absolutely, argue its supporters. Activists and thinkers have spent years working out detailed plans for how this could happen. There is massive public support - almost half the UK population wants the climate crisis to be addressed as urgently as the coronavirus was. The question is not, is there a way? But rather, is there the political will to make this happen?

Utopian - Impossibly perfect. The term comes from an ancient Greek phrase meaning "no-place" invented by Henry VIII's chancellor, Sir Thomas More, in 1516, as the name of an imaginary, ideal island.