Maritime shipping and commercial aviation contribute significantly to the global economy, making up about 16% and 4% of global GDP, respectively. Ships move 80-90% of the world's goods, and aviation transported 4.5 billion passengers annually at its peak before COVID-19 in 2019. However, both modes contribute a growing share of carbon dioxide (CO2) emissions.
Without urgent action, aviation and shipping will contribute a growing proportion of GHGs.
Aviation is currently responsible for about 3% of global energy-related CO2 emissions (about 1 gigaton, roughly equal to the annual emissions of Japan). This share is projected to rise to 4.5% by 2050 (2 gigatons) as the demand for air travel recovers from its COVID-19 slump and continues to increase. In addition to CO2 emissions, aviation also contributes to climate change via the warming effects of water vapor in contrails.
The use of passenger aviation is incredibly concentrated, too — in 2018, only 2 to 4% of the global population flew internationally. High-income countries are responsible for the largest share of aviation emissions. The United States alone contributes about 23%, and the next largest emitter is China at just over 10%.
In 2019, short-, medium-, and long-haul flights all emitted equal shares of CO2 emissions. Where possible, it is ideal to replace short-haul flights with bus or rail trips.
Maritime shipping accounts for almost 3% of global greenhouse gas (GHG) emissions. Roughly 85% of these emissions come from international shipping — the transport of goods by container ships, bulk carrier ships, and tankers.
Although shipping has become more energy-efficient since 2012, emissions from the sector could increase by up to 30% above 2008 emissions by 2050, due to increased demand for international goods. Notably, if we succeed in reducing the demand for fossil fuels, the decreased trade in fossil fuels may cut this demand growth.
Several new options for zero-emission aviation and shipping are emerging, but they need to be deployed at scale as soon as possible.
Shipping and aviation in a 1.5 degrees C (2.7 degrees F) world will constitute an efficient, well-run movement of people and goods with minimal CO2 emissions. To accomplish this, the world must decrease travel via planes using fossil fuel and ships using heavy fuel oil.
This includes reducing demand for travel, making operational and efficiency changes, and shifting air and sea travel to vessels using zero-emission options. Electricity, green hydrogen, ammonia, and, in some limited cases, advanced biofuels all hold potential. But because these solutions are either nascent or have not yet had commercial breakthroughs, additional public and private research and investment will be necessary to meet our climate goals.