Natural variations in the oceans in combination with rapid global warming due to greenhouse gas emissions were behind Earth’s record heat in 2023, report researchers in their new study published this week.

Every single month in the last six months of 2023 a new heat record was set. Last year was the warmest year on record, around 0.15 degrees warmer than the previous record year in 2016. A symbolic limit was also reached when Berkley Earth announced that 2023 would be 1.5 degrees warmer than pre-industrial times.

The new study, published in Nature Communications Earth & Environment, with Dr Laura Wilcox from the National Centre for Atmospheric Science along with research colleagues at CICERO, analysed the reasons behind the global temperature increase in 2023.

Dr Bjørn H. Samset from CICERO said: “Global warming really made a jump up in 2023. The question is whether this ‘jump’ is a sign of rapid changes in the climate system or our influence on it, or if it can be explained by natural fluctuations, such as the weather phenomenon El Niño, combined with the steady increase in temperature due to greenhouse gas emissions.” 

It was expected that temperatures would increase last year due to El Niño, but not by the large margin seen in 2023. In an attempt to explain this, scientists have asked whether the strong warming may be fully or partially explained by cleaner air around the world. Effective measures against air pollution are now being introduced in an increasing number of countries.

The same at sea, when cargo ships now switch to cleaner fuel. Aerosol particles in the air cause the warming that comes with emissions of greenhouse gases to be dampened. The particles reduce the amount of sunlight that reaches the earth’s surface and thus help to mask the effects of global warming.

Dr Laura Wilcox, Associate Professor at the National Centre for Atmospheric Science based at the University of Reading, explained: “Air pollution poses a serious health threat to millions of people. It is therefore good to have measures that provide cleaner air. But cleaner air can mean warmer temperatures as we lose the masking effect of aerosols. However, recent aerosol changes alone are not sufficient to explain the temperatures we saw in 2023.”

At the same time, the climate also has a number of natural fluctuations that affect the weather from year to year. El Niño, which occurs in the Pacific Ocean, is one of these, but there are others. In the study, the researchers used a method that makes it possible to quantify how ocean surface temperatures affected the record global
temperature increase in 2023.

The study covers the Pacific Ocean, the Atlantic Ocean, the Southern Ocean and the Indian Ocean. In all places, abnormally high surface temperatures were recorded at the same time. 

The research team found that the pattern of abnormally warm ocean water in 2023 was not unique, but similar to what we have seen before – precisely in previous years with record-high jumps in global temperature.   

Dr Bjørn H. Samset said: “Global warming continues, as rapidly as before. It is therefore essential that we cut greenhouse gas emissions in order to stop the climate changes that affect all life. In the future too, we must be prepared for strong jumps in temperature, with a rapid impact on extreme weather. This happens when global warming and weather variations pull in the same direction – as they did in 2023. ”