The latest carbon reduction agreement comes at the end of a five-day meeting at the International Maritime Organization's headquarters in London.
The gathering of the IMO's Marine Environment Protection Commission pitted climate-vulnerable nations - particularly islands in the Pacific - and richer countries against big exporters such as China.
The vast majority of the world's 100,000 cargo ships - which carry 90 percent of the world's goods - are powered by highly-polluting diesel.
Shipping, which is responsible for around three percent of global greenhouse gas emissions according to the U.N., is judged to be off course in the fight against climate change.
Compared with 2008 levels, the United Nations' global shipping regulator has agreed to cut total annual emissions of greenhouse gases "by at least 20 percent, striving for 30 percent, by 2030" and "by at least 70 percent, striving for 80 percent, by 2040."
The current target was a 50-percent reduction by mid-century, compared with 2008.
Shipping emits roughly the same level of greenhouse gases as aviation, which is aiming for net zero by 2050.
Environmental campaigners on July 3 protested outside the IMO's headquarters at the start of the group's meeting..
Several dozen activists, including some dressed as jellyfish, urged greener freight to help tackle climate change and protect the oceans.
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