A new study finds that reducing emissions from ships could actually do more harm than good when it comes to global warming.

Ships release sulfur, which can form bright, reflective particles in the air.

These particles bounce sunlight back into space, cooling the planet.

But ships also emit greenhouse gases, like carbon dioxide, which trap heat in the atmosphere.

The study found that if we reduce sulfur emissions from ships, it could actually make the planet warmer.

This is because fewer sulfur particles means less sunlight gets bounced back into space.

So, the cooling effect is reduced.

But the greenhouse gas emissions are still there, trapping heat in the atmosphere.

As a result, the planet ends up warming faster than we thought.

Overview

Since 2020, there has been a notable decrease in sulphur dioxide emissions from ships. This reduction, while intended to cut down on air pollution and improve human health, may have an unexpected consequence of accelerating global warming.

Some scientists argue that the resultant drop in sulphur dioxide, which previously helped cool the Earth by reflecting solar radiation, could lead to higher global temperatures.

Tianle Yuan from the University of Maryland, Baltimore County, notes that this decade may end up being unusually warm. This anticipated temperature increase is partly due to ongoing greenhouse gas emissions compounding the effects of reduced sulphur dioxide levels.

Yuan draws parallels with the hypothetical scenario of a sudden end to a solar geoengineering project.

However, not all experts agree with this dire projection. Laura Wilcox from the University of Reading points out that while the study is timely, its claims about temperature shifts and geoengineering are somewhat overreaching given the current evidence.

This issue traces back to an International Maritime Organization (IMO) regulation introduced in 2020—a rule aimed at reducing deaths linked to air pollution from ships.

Though effective in reducing health hazards, this regulation inadvertently took away the cooling properties of sulphur aerosols. These aerosols played a part in reflecting sunlight and making oceanic clouds brighter, which helped cool the planet.

Researchers employed satellite data and mathematical models to estimate the warming effect of the IMO rule. Their findings suggest that the oceans are absorbing more solar energy than before, particularly in heavily trafficked shipping lanes like the North Atlantic.

This region has seen a warming influence more than three times the global average.

By using a simplified climate model, Yuan and his team estimated that the temperature rise due to the 2020 changes could be about 0.16°C in the following seven years. This estimate is notably higher than some previous calculations, which highlighted the complex nature of climate response to such interventions.

Michael Diamond of Florida State University backs that the model’s predictions align with other studies observing post-2020 cloud changes.

Yet, some researchers have concerns about overestimating the warming effect. Zeke Hausfather of Berkeley Earth criticizes the conflation of ocean-specific warming with overall global temperatures, suggesting the actual increase might be closer to 0.1°C.

If the higher projections hold true, they could help explain the significant temperature increases seen in recent years. While rising greenhouse gases and El Niño conditions play a major role, the reduction in shipping emissions might be a missing piece of the puzzle.

Gavin Schmidt from NASA adds that while these changes might bridge part of the gap causing recent temperature spikes, they don’t account for all temperature anomalies.

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