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Why 2023 is shaping up to be the hottest year on record

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London saw high temperatures on 9 June 2023

Guy Corbishley/Alamy

Spiking temperatures in the world’s oceans and the arrival of El Niño weather conditions in the Pacific mean that 2023 is shaping up to be the hottest year on record, with researchers saying the planet is entering “uncharted territory”.

The previous hottest year on record was 2016, which is also when the world was last in a warming El Niño weather pattern (although some agencies say 2020 also tied for the top spot). Now, temperature records this month suggest 2023 could be tracking close to 2016. The first 11 days of June registered the highest global temperatures on record for this time of the year, according to Copernicus, the European Union’s Earth observation programme, following on from the second-warmest May on record and the fourth-warmest April.

The peak occurred on 9 June, when the average global air temperature was 16.7°C (62°F), just 0.1°C below the warmest ever recorded on 13 August 2016.

It is important to note that, while human-driven climate change continues to raise global temperatures, there is no evidence to suggest that the process is accelerating this year. Instead, specific warming conditions are being layered on top of the 1.3°C temperature rise caused by climate change so far, pushing records ever higher.

One of the main drivers of the recent extraordinary surge in heat has been the warmth in and above the oceans. For months, scientists have been warning that sea surface temperatures have been at record highs, driven by a series of marine heatwaves around the world. In the North Atlantic on 11 June, temperatures reached a high of 22.7°C, 0.5°C above the previous June high set in 2010.

It isn’t yet clear why the oceans are so hot right now, particularly given that El Niño conditions, which drive warmer sea temperatures, have only just arrived and won’t peak until the end of the year,

Weaker trade winds caused by changes in atmospheric dynamics is perhaps the most likely explanation, says Samantha Burgess at Copernicus. In the North Atlantic, a slump in wind strength may have reduced the amount of dust blowing through this part of the ocean from the Sahara, dust which usually has a cooling impact on ocean temperatures.

The surge in ocean and air temperatures is “surprising” for the time of year, says Burgess. Globally speaking, the first few days of June breached a 1.5°C increase in temperatures compared with the same time of the year in pre-industrial times – a threshold only previously surpassed during northern hemisphere winters, when temperature anomalies are more common.

“What we’ve observed to date is suggesting that 2023 will be probably in the top five warmest years,” says Burgess. “I think it’s fair to say that we are in uncharted territory. No one in human history has ever seen ocean temperatures this warm, and the air temperatures that we’re seeing as well are coming up to record-breaking.”

Although the broad drivers of warming – El Niño conditions plus climate change – are the same as in 2016, this year the heat is manifesting very differently. Whereas in 2016 spikes in temperature were concentrated over the Siberian Arctic, in 2023 the warmth has been seen in multiple spots, including in the Southern Ocean and Antarctica earlier this year.

Over recent months there has been growing concern over the lack of Antarctic sea ice, with February 2023 setting a new all-time record for minimum sea ice of just 1.79 million square kilometres. Sea ice is now reforming as the continent moves into its winter, but it is still tracking well below average.

“I think the general parallel is that we have this atmospheric variability, particularly with El Niño, on top of the background of the general warming trend. That’s the same as it was seven years ago,” says Christopher Merchant at the University of Reading, UK. “There is a good chance that we’re heading for another record-breaking year, this year or next year.”

As El Niño builds over the coming months, scientists expect to see more temperature anomalies appearing as its warming influence starts to tilt weather patterns around the world. “On top of the world as a whole being slightly warmer, you tend to get regional weather patterns, which gives you climate anomalies,” says Manoj Joshi at the University of East Anglia, also in the UK.

But the exact way in which the warmth manifests won’t be the same as in 2016, says Merchant. “I think there are unlikely to be parallels in the exact patterns of warm ocean temperatures or land temperatures, because the climate doesn’t really repeat like that.”

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