Reductions in shipping pollution in 2020 caused a “termination shock” that likely doubled the rate of global heating, according to new research.
In 2023, ocean surface temperatures hit record highs, puzzling experts and dividing them on whether the cut in shipping pollution is a major cause.
The research, published in Communications Earth & Environment, used satellite observations and computer modelling to assess the impact of the curtailing of the shipping pollution on heating weather.
Before 2020, global shipping relied on high-sulphur fuels that created air pollution, which blocked sunlight and increased cloud formation, thereby mitigating global heating.
However, new regulations introduced in early 2020 reduced the sulphur content in these fuels by over 80 per cent.
Researchers describe the sudden drop in pollution as an inadvertent geoengineering experiment, providing new insights into its effects and risks.
The research claims that the reduction in shipping pollution increased the heat trapped at the Earth’s surface, exacerbating the climate crisis.
The study’s authors believe it could be a "pretty substantial" factor, while others see it as minor, leaving the dramatic rise in temperatures largely unexplained.
Dr Tianle Yuan of the University of Maryland, who led the study, reported that the estimated 0.2 watts per square metre of additional heat trapped over the oceans due to the pollution reduction was "a big number," causing a significant shock to the climate system within a year.
"We will experience about double the warming rate compared to the long-term average since 1880," he said.
The heating effect from the pollution cut is expected to last around seven years.
The research found that the short-term shock accounted for 80 per cent of the total extra heating the planet has experienced since 2020, alongside longer-term factors like "rising" fossil fuel emissions.
Using simple climate models, scientists estimated that the reduction in pollution would raise average global surface temperatures by about 0.16°C over seven years. This increase is significant and matches the margin by which 2023 broke the previous temperature record.
However, some scientists believe the impact will be much lower due to climate system feedbacks, which are included in more advanced climate models. Results from this more detailed analysis are expected later in 2024.
"[Pollution particles] are one of the largest uncertainties in the climate system, and pretty hard to measure," said Dr Zeke Hausfather, at analysts Carbon Brief, according to The Guardian.
"The [pollution cut] is certainly a contributing factor to the recent warmth, but it only goes a small way toward explaining the 0.3C, 0.4C, and 0.5C margins of monthly records set in the second half of 2023," he said.
Dr Gavin Schmidt, at Nasa’s Goddard Institute for Space Studies, said the new research was "definitely a positive contribution, but it’s not using a fully coupled climate model, so there is still more work to be done. We’ll see how this all gets reconciled over the coming months."
Deliberately pumping aerosols into the air over oceans to increase cloud cover has been suggested as a method to cool the Earth.
"We did inadvertent geoengineering for 50 or 100 years over the ocean," Dr Yuan said.
Image Source: Unsplash
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