Five years ago, the United Nations Paris climate agreement set a ceiling for global warming at well below 2 °C, ideally 1.5 °C relative to pre-industrial levels.

To achieve this everyone from the United States, China, the European Union, to the technology firm Microsoft and even an alliance of European airports are saying they will achieve “net-zero” greenhouse gas emissions this century.

But what is Net Zero? And is it the solution to global warming?