For many people, 2023 – confirmed by Nasa as the hottest on record – was marked by extreme weather, sweltering heatwaves and wildfires. It also saw climate scientists alarmed by a viral chart on social media showing just how far the North Atlantic's sea surface temperature was deviating from the historic average.
The chart was initially shared by Dr Thomas Smith, associate professor in environmental geography at the London School of Economics, in April and was one of many, similarly alarming ones illustrating that the temperature of the world’s ocean surface had hit a record high – and wasn't showing any signs of abating.
This is so unusual. That's a *huge* amount of energy being transferred to the atmosphere. Expect extreme temperature and storm records. Just the top few metres of our oceans store as much energy as the entirety of our atmosphere. I'm very concerned for later this year into 2024. https://t.co/7rfyJeZMaA
— Dr Thomas Smith 🔥🌏 (@DrTELS) April 24, 2023
Rises in sea surface temperature (SST) are important, as the US Environmental Protection Agency puts it, because can have "profound effects" on global climate. They can lead to an increase in the amount of atmospheric water vapour over the oceans and, in turn, a greater likelihood of extreme weather events such as heavy rain and snow.
In addition they can shift storm tracks, potentially contributing to droughts in some areas, as well as prolonging bacteria growth, which can contaminate seafood and cause food-borne illnesses.
In fact, the Bulletin of the Atomic Scientists on Tuesday cited SST as one of the reasons their "Doomsday Clock" remains set as close to midnight as ever before.
On 21 January 2024, Dr Smith shared an update to his viral post from 2023, saying: "This tweet went viral & made the news in June 2023, two months after my first concerns about sea surface temperatures."
He went on to share this updated version of the chart, which doesn't make for pleasant viewing.
— Dr Thomas Smith 🔥🌏 (@DrTELS) January 21, 2024
"Seven months have passed since then & the North Atlantic has now spent 321 consecutive days breaking daily SST records. This year has shown no signs of improvement, with new data for 2024 showing a persistent pattern of record-breaking temperatures," Dr Smith added.
So why has 2023 and 2024 seen records broken so consistently?
Last year saw El Niño – a climate pattern which occurs every two to seven years – driving up ocean and air temperatures, and a high-pressure system over the Atlantic will have made a difference.
However, there's potentially another factor at play, according to Dr Smith, which he and other scientists say may have been overlooked for several decades.
He told Yahoo News UK this week: “In the past few years there seems to be a lot more sunlight being absorbed by the surface of the ocean. This coincides with the shifting regulations around shipping fuel, and I think it would be prudent not to ignore that coincidence."
The decision taken in 2020 to clean up international shipping by cutting sulphur dioxide (SO2) emissions was made to improve air quality and protect people's health from this hazardous gas. However, Dr Smith warns it could have had an unintended impact on climate change that had been "masked" for many years.
"We know that aerosols – particulates in air pollution – are important for reflecting sunlight. [They] are also important for formation of cloud, which reflects sunlight in the lower parts of the atmosphere." This, he says, means such pollution has likely been "helping to keep us cooler than it would have otherwise been".
“This was a much bigger effect during the 1950s and 1960s when industry and transport was far more polluting than it is today, and we think that that might have delayed greenhouse warming by a few decades before we started cleaning up the atmosphere.
EU fossil fuel CO2 emissions hit 60-year low (The Guardian)
“But once we started cleaning up the atmosphere of the particulate pollution, it's the warming effect of the carbon dioxide that then begins to the dominate the global temperature pattern.”
While there is no unanimous scientific consensus on this potential phenomenon, Dr Smith points to a 2023 study, published in Oxford Open Climate Change, which describes this tussle between less air pollution and increased warming as a "Faustian bargain". The paper suggests the decline in aerosol emissions since 2010 should increase the rate of warming, which means that we could reach 2C above pre-industrial levels by 2050.
"Of course, we desperately want to avoid that by 2100, so if that happens sooner then we could be in for some extreme weather," said Dr Smith. He warned that hitting 2C by the middle of this century would be "far quicker than most governments are planning for".
How could we get out of this?
The best option is to achieve net zero as soon as possible, Dr Smith says, adding: "It is really important to understand that the long-term problem here is the greenhouse gases."
Others believe another potential solution is geoengineering, something Dr Smith stressed he does not endorse. "That might include reintroducing particles into the ocean atmosphere, but maybe cleaner particles such as salt crystals. So using a fine ocean spray to help create clouds that have disappeared as a result of the cleaner fuels."
He says "more extreme" options include putting aerosols into the stratosphere, similarly to a volcanic eruption, which can contribute to temporary cooling. "There are some people again advocating continuously spraying the stratosphere with these reflecting aerosols to offset the greenhouse warming and give us a bit of time to reach net zero."
Ultimately, Dr Smith says we should all be making decisions as individuals to reduce our CO2 emissions, and says governments should be introducing carbon taxes to help fund offsetting measures. "There is very little incentive people to cut down their carbon footprints." he adds.
For decades this area has been kept relatively cool by sulfur emissions from ships.
But this changed in 2020. pic.twitter.com/DFD39uyVJ3
— Leon Simons (@LeonSimons8) March 8, 2023
'More than just an inconvenience'
When asked what we could expect to see in a worst-case scenario, with global temperatures rising above 2C by the middle of the century, The worst-case scenario is a concerning picture.
“Your biggest concern has to be food and water security," Dr Smith explains. "This is why people do need to be worried about 2C of warming. We’re not talking about an inconvenience.
"We’re talking about whether you can buy food in the supermarket or have clean water coming out of your tap. We’re already having problems in some places with 1C of warming. We could be seeing the loss of 30-40% of the world's carbohydrate production with 2.5C."
Dr Smith isn't the only one saying this. A recent study by NASA warned that if temperatures keep exceeding 2C, we could face a multitude of problems all at once. “The escalating impacts of all the climate extremes studied could cause significant damage to communities and economies, from fires, floods, landslides, and crop failures that may result," it says.
Parliamentary research also warns that climate change means "frequent and severe extreme weather events are expected to increase 'forcible displacements', and the 'slow onset' impacts of climate change are expected to make the hardest hit regions uninhabitable".
Dr Smith adds: “We are not talking about kind of small changes that you might have to make. It’s fundamentally whether you can buy food in an economy that’s dependent on imports. I’d prefer we don't get that far… I’d prefer our security to be maintained, and part of that includes mitigating climate change as fast as we can.”