quixoticgeek, 
Shipping is 1.8% of global emissions. That's less than air travel. Reducing that by a third is a 0.6% drop. Noise compared to many other areas.
50% of shipping is moving fossil fuels. If we stop extraction of fossil fuels. Then we can halve our emissions from shipping overnight.
But we really need to focus on other areas, the gains here are tiny. Fix surface transport (hint, build more trains). Or steel production.
