An agreement to cut the shipping industry's greenhouse gas emissions by 50 percent — from 2008 levels — by 2050 will not be easy, but it can be done, a Norwegian minister said.

"Ambitions for 50 percent reduction by 2050 are definitely difficult, but it's achievable. And now we have a situation where we really have to start with developing green shipping that we need for the future," Norway's Minister of Climate and Environment Ola Elvestuen said.

The International Maritime Organization's decision on this agreement will be in line with the Paris Agreement on climate change, he said.

Although it has traditionally been difficult to agree on a universal method to measure emissions in the huge and diverse shipping and aviation industry, Elvestuen said that will be worked on.