Maybe targeted at Americans and using US customary short tons (which is 907 kg)
As an American, I'm going to need this as a volume, either in terms of Olympic-sized swimming pools or the height of a pile in an [American] football stadium. Maybe I'd accept weight as a quantity of Ford F-150s, but you'd be pushing it.
4,000 tonnes is almost exactly 4 tonne. Could be 4,0004 tonne.