The best you can do with a single number would be something like 6·10^2 tons, you also use 6 hectotons or 0.6 gigagram though people might find those a bit weir

The best you can do with a single number would be something like 6·10^2 tons, you also use 6 hectotons or 0.6 gigagram though people might find those a bit weird. Or you could just denote its accuracy, which the original source likely does, but which news article inevitably fail to include (and subsequently fail to adjust the number of significant digits).