Meet the 73-year-old Australian scientist who's developed a special kiln that he reckons will solve Australia's iron ore emissions problems and deliver green iron.

For more on the episode, visit the Tech Zero site on afr.com. AFR subscribers can also sign up for the weekly Carbon Challenge newsletter. 

Correction: This episode credited former US Secretary of State Colin Powell with popularising the concept of "unknown unknowns". The phrase was in fact brought to popular attention by former US Secretary of Defence Donald Rumsfeld.