The study was prepared by Shrewsbury-based John Whitelegg, a visiting professor in the School of the Built Environment at Liverpool John Moores University.
He prepared the report as part of his new role as "Fellow in Transport and Climate Change" at the Foundation for Integrated Transport.
With Shropshire Council, like many other authorities, having declared a climate emergency, it has questioned as to whether a project producing a large amount of carbon emissions would be wise.
Professor Whitelegg said: “This additional burden of 93,791 tonnes of CO2 is an avoidable and unacceptable move in the wrong direction.
"Decarbonisation and dealing with climate change requires a reduction in carbon and not a policy that increases those emissions by 93,791 tonnes of CO2eq.”
Shropshire Council maintains the £87.2 million road, stretching from the Welshpool Road roundabout to the Ellesmere Road roundabout, will benefit the town by reducing traffic and lead to a “net gain” for ecology and biodiversity.
Councillor Dean Carroll, the council’s cabinet portfolio holder for climate change, said recently: “One of the overriding principles of the NWRR is about moving traffic out of Shrewsbury town centre.
“That will have the benefit of improving the air quality and reducing the CO2 impact of journeys between the north and west of Shrewsbury.”
He added: “It will reduce the stationary and stop-start times that are currently such an issue for the vehicles passing through the town centre and will enable them to be much more fuel efficient.”