Efforts to clean up the shipping industry by removing sulphur from fuel paradoxically led to increased heat stress on the Great Barrier Reef during a 2022 bleaching event, according to a new study published in the Nature journal Communications Earth & Environment.
The study, led by Dr. Robert Ryan, an atmospheric scientist at the University of Melbourne, found that the removal of sulphur from shipping fuel caused “a lot of extra sunlight” to hit the reef, subjecting the corals to up to 10% more heat stress.
In 2020, the International Maritime Organization introduced regulations to cut the amount of sulphur allowed in fuels from 3.5% to 0.5%. Sulphur pollution can cause respiratory problems for humans and acid rain, but it also has a shading effect, making clouds brighter and providing more shade to areas underneath.
During the early months of 2022, the Great Barrier Reef suffered its sixth mass bleaching event, the first to occur in a typically cooler La Niña year. Ryan and his colleagues analysed data from around 5,000 ships in the region between 18 and 28 February 2022, when heat was building up on the reef.
Using computer models, the researchers found that the prevailing winds in the region would have blown the reduced sulphur emissions over the reef, allowing between 5% and 10% more of the sun’s energy to hit the reef’s waters compared to what would have happened without the new regulations.
“Nothing happens in isolation. There’s no such thing as a free lunch,” Ryan said, emphasising that emissions of CO2 and air pollutants need to be reduced simultaneously.
Professor Steven Sherwood, a climate scientist at the University of New South Wales who was not involved in the research, said the study highlights that while the overall effect of removing sulphur on global temperatures is small, the local impact on ocean temperatures in the tropics can be larger.
“This is an important result since it shows the impact on corals might be nontrivial even though the overall global warming impact is pretty small,” Sherwood said.
The findings underscore the complex and interconnected nature of environmental issues, where efforts to address one problem can sometimes have unintended consequences on other ecosystems. As the world continues to grapple with the challenges of climate change and environmental protection, this study serves as a reminder of the need for a holistic and well-informed approach to policymaking.
