As global temperatures continue to rise due to increased concentrations of greenhouse gases (GHGs), various sectors and industries are pulling together to rethink business-as-usual. One crucial strategy among them you may have heard about: decarbonization.
Decarbonization is the process of reducing carbon dioxide (CO2) emissions to achieve a lower output of GHGs into the atmosphere. It involves the adoption of sustainable low-carbon power and fuel sources. Numerous sectors are grappling with how to decarbonize quickly and the maritime industry is no exception. With such a foundational role in global trade and supply chains, maritime decarbonization is critical to decarbonizing the global economy as a whole.
Annually, large transport and cargo ships transport $4 trillion worth of goods across our seas—everything from food and clothing to building supplies, medicine, and more. Mammoth container ships can stretch the length of five city blocks and carry more than 20,000 containers each. Collectively, they transport approximately 80% of global trade by volume.
Along the way, these ships emit more than one billion tons of GHG emissions into the atmosphere, or nearly 3% of emissions worldwide. Under business-as-usual scenarios, emissions are expected to rise through the next several decades.
In 2018, the International Maritime Organization (IMO), an international agency responsible for regulating shipping, set an ambitious goal—to cut GHG emissions by at least 50% by the year 2050, relative to a 2008 baseline. Hitting this target will require a shift away from the petroleum-based fuels like diesel and heavy fuel oil that are the industry standard today. New fuels and energy efficiency measures must be adopted. Swift action and coordination among multiple stakeholders across the maritime industry, government, and research and academic institutions is required to successfully navigate this one-in-a-century energy transition.
The challenge ahead for the shipping industry may seem formidable now, but history is riddled with examples of how the maritime industry has navigated major transitional periods of the past.
Cargo ships harvested wind energy to power their sails until about the 19th century, when they began to be replaced by faster steamships. The next major transition wasn’t until the latter half of the second century when motor ships using internal combustion engines became the predominant commercial vessels of choice. Ironically, it was around this same time that scientists began sounding the alarm about the increasing evidence of the warming effect of GHGs in the atmosphere.
Heavy fuel oil has been the dominant fuel in the industry since the 1960s due to its low cost, energy density, and widespread availability. This thick, tar-like substance is a residual fuel that is left over from refinement of other lighter distillate fuels and often contains heavy metals and other compounds that lead to harmful air pollution when used for combustion. Heavy fuel oil’s dominance in the maritime industry may be starting to wan, however. Industry regulators and ship operators are beginning to recognize the only viable future is one in which low-carbon fuels are the dominant choice. Alternative fuels are just one of several pathways for maritime decarbonization—other possible pathways include electrification and energy efficiency. Each will have a role to play in the maritime energy transition.
Cargo ships that use heavy oil fuel emit sulfur dioxide as a byproduct, a toxic pollutant linked to acid rain, respiratory illness, and premature morbidity and mortality rates. That’s in addition to the carbon dioxide and methane they exhale, gases which trap heat in the atmosphere and accelerate the impacts of climate change. Transitioning to cleaner fuels could significantly reduce air pollution caused from maritime transportation overall. To meet international regulations around allowable sulfur content, some ship owners have opted to install exhaust gas cleaning systems, or scrubbers, that remove excess sulfur oxides (SOx) from the exhaust gas before releasing it into the atmosphere. These exhaust gas cleaning systems often use seawater to remove sulfur which is discharged back into the ocean, leading to pollution in marine environments. Nitrogen oxide (NOx) is another known pollutant emitted by ships that’s responsible for toxic algal blooms in coastal waters and inland lakes. Scrubber discharge water and NOx pollution could both be reduced or eliminated entirely with the use of cleaner alternative fuels.