Current international trade relies heavily on ocean shipping, and cargo ships using fossil fuels are emitting large amounts of greenhouse gases. In order to reduce carbon emissions and slow the rate of warming, the future of ocean shipping may rely more on clean energy sources such as wind and electricity.

Shipping accounts for nearly 3 percent of global greenhouse gas emissions and produces as much carbon dioxide as all U.S. coal-fired power plants combined. Still, shipping's share of greenhouse gas emissions is not high in a transportation sector that accounts for 37 percent of global emissions.

However, with the continued growth of international trade and heavy reliance on ocean-going vessels to transport goods, many scientists warn that shipping could account for 17 percent of total greenhouse gas emissions by 2050. Currently, more than 80 percent of all cargo is transported by ocean-going vessels.

For this reason, regulators of the shipping industry are stepping in after years of ineffective decarbonization efforts.In 2018, the International Maritime Organization (IMO), a London-based U.N. agency, set a goal of reducing greenhouse gas emissions by 50 percent from 2008 levels by 2050.

But critics argue that the target is too small and too late to achieve it. They insist that the IMO should reset its goal to achieve 100 percent decarbonization by mid-century, and of course the sooner the better.

In terms of developing climate measures and strategies, the IMO is quite late to the party," said Lucy Gilliam, director of shipping policy for the environmental NGO Seas at Risk and a board member of the Clean Shipping Coalition. "

The shipping industry is beginning to establish "green corridors," specific shipping routes and ports that support zero-emissions solutions and policies. The financial community has also joined the decarbonization movement, with 29 institutions signing on to the Poseidon Principles, an agreement that will consider shipping companies' efforts to reduce greenhouse gas emissions when lending to them.

The signatories represent more than $185 billion in international shipping loans, almost half of the amount financed by the global shipping industry.

But with global supply chains designed for fast delivery, many major breakthroughs are being bet on the development of low- or zero-emission fuels, including environmentally friendly methanol, hydrogen, liquefied natural gas (LNG) and ammonia, to reduce or replace the fossil fuels used in the large diesel engines on most ships. These efforts include electric and wind propulsion technologies.