At the moment there are simply no cheap and widely available solutions to significantly reduce the emissions of the shipping industry. In the future? Absolutely. The research into clean(er) fuels is still very young, and while there are some applications already, it will take a while to find the best alternative that is clean, has high energy density, and is affordable enough. Hydrogen, ammonia, methanol are probably the only realistic option at this point, but each of them also has specific disadvantages. The biggest issue imo is that the whole infrastructure will need to be changed, from how the ships and engines are built, to the fueling infrastructure in all the ports worldwide. This will certainly take time...
Safe nuclear propulsion would be a dream, and new developments in nuclear technology should enable it, if the public accepts it. Molten salt reactors sound like a great prospect - non-weapon grade, low risk of explosions, operates at atmospheric pressure, no leaks of radioactive steam and cooling water, reduced size, generates much less and shorter-lived radioactive waste, higher efficiency, cheaper than conventional reactors, plentiful in nature, potential to consume nuclear waste.