This will increase carbon emissions. Shipping is the slowest, cheapest, least carbon intensive mode of transport per ton. Adding a tax to the greenest available option is as silly as tax on wind turbines.
The tax isn’t remotely large enough to result in freight migrating to air. And trucking within the eu is already subject to a carbon tax.
I like the framing ;-) Maybe it could work for climate change deniers: “Tired of THE MAN intruding on your personal freedom to pollute? Regain your independence with solar, electric transport, good insulation, and a low impact diet. Freedommmmm!”