The way I read it, he's deliberately using big language to try and drum up international support for his position on Iraq. There's no threat there, at least, not from him.
I'm intrigued by what method he expects "World War Three" to begin. I'm assuming the idea is
Iran Nukes Israel
America invades Iran
Nuclear fallout and massive refugee crisis ****s up the middle east and world oil supplies are affected.
Oil prices surge.
Resource war commences.
But, to be honest, I don't see it happening. Global oil prices would rise, yes, but net result would be people using less oil - so far we've swallowed price rises, but there has to come a point where it simply becomes too expensive to use oil for most of the things we do now. Net result wouyld probably be a 20 year recession while alternative energies come on line (with R+D hastened by desperate need) followed by... business as usual I suppose. Bad, but not world war three. Moreover, I suspect if the Iranians do nuke Israel, it'd be with a bomb designed to minimize fallout (otherwise it'd land on Iran as well), so the level of overall regional radioactive damage would probably be minimal (reducing the refugee crisis and oil supply problems).
The only other way I can see it happening is via the China-Russia-Iran love triangle, plus emerging US-russian tensions and China's Taiwan lust. However, a military response to a nuking of Israel would probably be a UN backed operation, and, in all likelihood, would have Russian and Chinese support anyway. So I think we're fairly safe on the nuking of Israel bit. We don't have to worry about WWIII until oil supplies get low enough to convince either China or Taiwan to make a serious play for the Spratley Islands. Then we're all going down.