Efforts to clean up our oceans might be accidentally speeding up global warming. Umm, but how, why? I had the exact same question when I came across this article from Financial Times, and I tried my best to understand it and now I’m trying my hand at explaining it. I am by no means an expert but here is what I have understood.
In 2020 the International Maritime Organisation (IMO) decided to reduce sulphur emissions from ships. While this move was intended to reduce the pollution from our oceans, climate scientist James Hansen has raised some concerning questions about its second order effects.
To understand this, let’s first look at how sulphur actually affects our climate. When ships release sulphur, it creates something called sulphur aerosol - think of these as tiny, invisible particles floating in the air, similar to dust. These particles actually play an interesting role in protecting our planet from heat. It’s a bit like holding up a thin umbrella on a scorching hot day - while it won’t make the day cool, it definitely helps reduce the heat you feel on your body.
Hansen argues that by reducing the sulphur content in ship fuel - a well-intentioned move to curb ocean pollution - we have accidentally removed this protective “umbrella” over our oceans. With less sulphur aerosol in the atmosphere, more sunlight is now reaching and heating our oceans.
This could be the potential explanation for why you feel like there are two seasons now: summer and very hot summers. Scientists had predicted that the effects of El Niño (a natural warming phenomenon) would begin to decrease, but January 2025 remained the hottest January ever recorded. This suggests that even as El Niño’s influence should be reducing, temperatures aren’t dropping as expected. Hansen believes the reduction in sulphur aerosol could be the reason why we’ll continue to see rising temperatures, making the international goal of limiting global warming to 2°C essentially unattainable.
Hansen describes this situation as a “Faustian bargain” - a bad deal where humanity temporarily benefited from the cooling effects of air pollution while continuing to emit greenhouse gases. Now, as we clean up certain types of pollution (which we absolutely should), we’re starting to see the full impact of our greenhouse gas emissions. If you wish to do a deep dive, you can find Hansen’s research paper here.
However, it’s worth noting that not everyone thinks similarly. Some scientists argue that Hansen is overestimating the impact of reduced sulphur aerosol on global temperatures.