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Progress toward the target will be measured against a 2008 fleet baseline, and emissions rates will be calculated based on the industry fleet's total carbon emissions, total ship berths and total distance travelled.
Cruise Lines International Association said it aspired to the International Maritime Organisation's vision of a carbon-free shipping industry by the
end of the century.
The 40 per cent commitment was a first step towards realising that.
While CLIA cruise lines each had sustainability programmes to reduce waste the commitment to reduce the rate of carbon emissions is the first initiative they had taken together.
The association's Australasian managing director, Joel Katz, said no industry had a stronger interest in protecting oceans than cruising.
''It is not simply our responsibility: operating sustainably at sea is a business imperative. What other industries do on land, we must do at sea – a challenge that promotes constant innovation in our operations and advances environmental protection efforts."
Cruise lines are working towards cutting single use plastic and doing more recycling while new technologies in ship design and propulsion will help reduce emissions.
Ships use have traditionally used heavy oil but more are being built to run on liquid natural gas which generate significantly less emissions. The first LNG cruise ship, the AIDAnova, began cruising last month around the Canary Islands.
It is estimated 25 LNG-powered ships will be cruising by 2025.
Cruise lines are also installing advanced air quality scrubbing systems that reduce ship exhaust by up to 98 per cent.
Other technology, including a micro bubble system to reduce friction between the hull and the water, can help reduce fuel consumption by around 8 per cent.
The association represents about 95 per cent of cruise capacity, or about 24 million passengers a year.