Farmers also save a lot of fuel when they don't need to till their fields to control weeds. That means they spend less time operating the tractor and produce fewer greenhouse gas emissions. In just one year of growing Canadian canola, farmers saved one billion kilograms of carbon dioxide – that's equivalent to removing nearly 500,000 cars from the roads!
Source: Graham Brookes & Peter Barfoot (2015). Environmental impacts of genetically modified (GM) crop use 1996–2013: Impacts on pesticide use and carbon emissions. GM Crops & Food, 6:2, 103-133.