The leftist economist, Yanis Varoufakis, turned politician explains:
The money already exists. Up to 3 trillion euro is languishing in Europe's financial system doing nothing but harm (e.g. boosting share prices and house prices). By issuing green bonds worth 500 billion per year, the European Investment Bank, which belong to all Europeans, can soak up all this money and put it to work for the environment and for Europeans. The European Central Bank can also help simply by standing by to prop these bonds up, as it has been doing since 2015.
Yanis is making it easy for Europe to do this. He's not holding out for just printing the money without issuing bonds (without increasing public debt). He's making it easier politically. There's really no excuse for Europe to not do this other than the greed of carbon-fuel executives and shareholders and others who profit from pollution.