"Unless you have a 75 percent cut in the highest tariffs there would be very little outcome at all," Will Martin, lead economist of the World Bank development research group, told Reuters in an interview.
WTO members are due to meet in Hong Kong in December to put together a deal that would lower global trade barriers in an attempt to lift millions out of poverty. But efforts to agree first on cutting rich nations' farm subsidies and duties have run into trouble.
Market access, or lowering duties on imported farm goods, is a major sticking point. The United States is calling for cuts of 90 percent on the highest tariffs and the EU is saying it would only go to around 50 percent on its top tariffs.
"A 50 percent cut in tariffs is nowhere near enough," Martin said. "The 75 percent would generate global welfare gains of about $75 billion out of a potential welfare gain of $182 billion if you had complete liberalisation of agriculture."
Citing figures from research just completed by the World Bank, Martin added this scenario envisaged no special protection for particular commodities, or politically sensitive products.
The report also found that removing cotton subsidies would allow developing countries to raise their share of global exports to 85 percent in 2015 instead of 56 percent, and would raise the export price of cotton.