by The reduction in pollution from shipping in 2020 led to a major “termination shock” that is thought to have pushed the rate of global warming to double the long-term average, according to research.
Until 2020, global shipping used dirty, high-sulfur fuels that produce air pollution. The polluting particles blocked sunlight and helped create more clouds, limiting global warming. But new regulations at the beginning of 2020 reduced the sulfur content of fuels by more than 80%.
The new analysis calculates that there has been a significant increase in the amount of heat trapped on the Earth’s surface which is driving the climate crisis due to the subsequent fall in polluting particles. The researchers said the sharp end to decades of shipping pollution was an inadvertent geoengineering experiment, revealing new information about its effectiveness and risks.
Record high sea surface temperatures hit 2023, alarming experts who struggled to explain the huge increases. But scientists have mixed views on the role of reducing shipping pollution.
The people behind the new study say it could be a “quite substantial” factor. Others say it’s only a small factor, and that the reasons for the unusual rises in ocean and global temperatures remain a terrifying mystery.
Dr. Tianle Yuan, at the University of Maryland, USA, who led the study, said that “a large number of the 0.2 watts per square meter of additional heat that was trapped over the oceans after the reduction in pollution, and it happened in one year, then. it’s a big shock to the system”.
As a result, “we will have about twice the rate of warming compared to the long-term average” since 1880, he said. The heating effect of the polluted cut is expected to last for about seven years.
The research, published in the journal Communications Earth & Environment, combined satellite observations of sulfur pollution with computer modeling to calculate the impact of the cut. The short-term shock was found to be equivalent to 80% of the total additional warming the planet has seen since 2020 from longer-term factors such as rising fossil fuel emissions.
The scientists used relatively simple climate models to estimate how much this would contribute to global average temperatures on the Earth’s surface, which found a rise of around 0.16C over seven years. This is a big increase and the same margin by which 2023 broke the temperature record compared to the previous warmest year.
However, other scientists think that the temperature impact of pollution reduction will be much lower due to feedback in the climate system, which is included in the most sophisticated climate models. Results of this type of analysis are expected later in 2024.
“[Pollution particles] is one of the biggest uncertainties in the climate system, and quite difficult to measure,” said Dr. Zeke Hausfather, at Carbon Brief analysts. He said the new analysis did a good job using satellite data to estimate the change in heat trapped after the pollution reduction, but he disagreed with how that led to a rise in temperatures. Hausfather’s estimate of the temperature rise due to the reduction in pollution was 0.05C over 30 years.
“The IS [pollution cut] It certainly contributes to the recent warmth, but it only goes a small way towards 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 “undoubtedly a positive contribution, but it is not using a fully coupled climate model, so there is still more work to be done.” We’ll see how this all pans out in the coming months.”
In March, Schmidt warned: “We need answers as to why 2023 was the hottest year in perhaps 100,000 years. And we need them fast. ” He said the recent El Niño event and increased solar activity were not adequately explained.
Deliberately pumping aerosols into the air over the oceans to encourage more cloud cover has been proposed as a means of cooling the Earth. Yuan said that years of shipping pollution and subsequent severe cutting was an accidental experiment on a large scale: “We have done careless geoengineering for 50 or 100 years over the ocean.”
The new analysis shows that this type of geoengineering would reduce temperatures, but also carry serious risks. These include the sharp rise in temperatures when aerosol pumping was stopped – the termination shock – and also possible changes in global precipitation patterns, which could disrupt the monsoon rains that billions of people depend on.
“We should definitely research this, because it’s a tool for situations where we want to temporarily cool the Earth,” like an emergency brake, he said. “But this will not be a long-term solution, because it does not address the root cause of global warming,” which is emissions from burning fossil fuels.
