This study assesses the potential economic and environmental impacts that would arise if restrictions on glyphosate use resulted in the world no longer planting genetically modified herbicide tolerant (GM HT) crops. ‘First round’ impacts are the loss of farm level and aggregate impacts associated with the widespread use of GM HT crops (tolerant to glyphosate). There would be an annual loss of global farm income gains of $6.76 billion and lower levels of global soybean, corn and canola production equal to 18.6 million tonnes, 3.1 million tonnes and 1.44 million tonnes respectively. There would be an annual environmental loss associated with a net increase in the use of herbicides of 8.2 million kg of herbicide active ingredient (+1.7%), and a larger net negative environmental impact, as measured by the environmental impact quotient indicator of a 12.4%. Also, there would be additional carbon emissions arising from increased fuel usage and decreased soil carbon sequestration, equal to the equivalent of adding 11.77 million cars to the roads.