What percentage of global emissions comes from shipping?

Shipping accounts for roughly 2 to 3 percent of global human-caused CO2 emissions, based on figures published by the International Maritime Organization. The IMO's Fourth GHG Study found that shipping emitted 1,056 million tonnes of CO2 in 2018, about 2.89 percent of total global anthropogenic CO2 emissions that year. Other assessments place the figure similarly, with the International Council on Clean Transportation putting shipping's share of global CO2 at approximately 2.3 percent as of its most recent data.

That share is expected to grow if left unaddressed. Transport & Environment and other groups tracking the sector have noted that shipping emissions could reach 10 percent of global greenhouse gas emissions by 2050 under current growth trends, since global trade volume keeps rising while other sectors decarbonize faster.

The scale of the problem is concentrated in a small number of large vessels. Container ships, tankers, and bulk carriers running on heavy fuel oil or marine diesel make up most of the sector's emissions, and most of the global fleet was built to run on those fuels.

This is the context behind efforts like Voltic's, a Boston-based company spun out of MIT's Ocean Engineering department that has patented a power system for zero-emission, fully electric retrofits of existing cargo ships. Because the existing fleet is large and mostly not due for replacement for years, converting ships already on the water is one path to cutting the sector's emissions share without waiting for a new generation of vessels to be built.