Say no more.

Gunns’ proposed pulp mill in Tasmania’s Tamar Valley will cost the island’s economy up to $3 billion if something goes wrong, according to a new economic analysis.

The results of the analysis, commissioned by the The Wilderness Society, are in stark contrast to a similar study done for Gunns.

The National Institute of Economic and Industry Research (NIEIR) analysis found the most likely outcome of the mill would be a cost of $300 million to the Tasmanian economy until 2030.

Institute head Dr Peter Brain estimated the mill would boost the economy by $1.3 billion in a best-case scenario and in the worst case, $3 billion.

An Allens Consulting Group analysis — commissioned by Gunns — predicted the most likely impact of the mill would be a gain of $3.3 billion.

Dr Brain took into account factors including the cost of lost tourism and the risk of chemical spillage, Gunns changing ownership, a blow-out in capital costs, deaths and sicknesses from environmental damage and the closure of two other paper mills in northern Tasmania.

Allens Consulting had underestimated the opportunity cost of logs consumed in the pulp mill, which could be exported as high-value timber, and the cost of agricultural land clearing, Dr Brain said.