2.5% would be far from insignificant. The European Commission Climate Action website put it closer to 2.9% and volumes are expected to increase by as much as 100% until 2050.

The percentage is even more significant if you look at it from the point of view of relatively clean part of the world like the EU. Shipping is 4% of our emission.

Something will definitely have to be done with shipping if countries want to hit their emission targets.