Global surface air temperatures crossed the key 1.5C warming threshold temporarily at the start of June, as the world’s oceans hit record-high temperatures for two months running.
If the trend continues, the level of global warming since the pre-industrial era presents a stark indicator of worsening climate change.
Scientists at the Copernicus Climate Change Service said the first 11 days of June had been the hottest on record for this time of year, and that the 1.5C warming threshold had been temporarily crossed.
The threshold was first exceeded during December 2015, and crossed “repeatedly” in 2016 and 2020. This year is the first time it has been breached in June.
The findings “should be a stern warning sign that we are heading into very warm uncharted territory”, said Melissa Lazenby, a lecturer in climate change at the University of Sussex in the UK.
The Paris Agreement commits countries to limiting long-term warming to 1.5C above pre-industrial levels, ideally. Long-term warming is already at least at 1.1C.
Global ocean temperatures, meanwhile, reached their highest levels on record for April and May, according to the US National Oceanic and Atmospheric Administration. Above normal sea-surface temperatures had “recently expanded across the central and eastern equatorial Pacific”, it said
Sea surface temperatures in the north Atlantic ocean rose to unprecedented highs in June
*Compared with the 1971 to 2000 average • Source: Noaa Physical Sciences Laboratory • Cartography: Steven Bernard © FT
Animated map showing sea surface temperature anomalies in the eastern Pacific and Atlantic oceans
Thomas Smith, a professor in environmental geography at the London School of Economics, noted that the top few metres of the ocean stored enormous amounts of energy, and warned that hotter water temperatures meant a very large amount would be transferred to the atmosphere.
Scientists this month declared the return of El Niño, the weather phenomenon that is associated with warming across the Pacific Ocean. But they said the recent record heat was not necessarily a direct result, since its effects were typically felt after it had been active for some time.
“There tends to be a lag,” said Rocky Bilotta, a climatologist at NOAA. El Niño was likely to have “more influence on the 2024 season of global temperatures rather than currently in 2023. But that doesn’t necessarily mean that we’re not already seeing an effect,” he said.
The LSE’s Smith said the unusually warm Atlantic and Indian oceans meant that “this El Niño may not be like others” as the warming effect takes hold over the Pacific Ocean.
“The unprecedented situation presents a challenge for those forecasting weather conditions in the months that lie ahead,” he said.
NOAA said there was a more than 90 per cent chance that El Niño would persist into 2024.
That has fuelled concerns about unprecedented heat this year and next. 2022 was the fifth warmest year on record despite the cooling effects of the La Niña weather phenomenon — El Niño’s opposite — that was present for three consecutive years.
“With the emerging El Niño there is a possibility that the average surface global temperature for the whole of this year or next could exceed 1.5C for a single year,” said Albert Klein Tank, director of the UK Met Office Hadley Centre for Climate Science and Services.
Global land and ocean temperatures were the third warmest on record for the March to May period, and there was a 99.5 per cent chance that 2023 would be a “top 10” hottest-ever year, said NOAA.
About a quarter of the contiguous US is in a state of drought, while ferocious wildfires have ripped across vast tracts of Canada and unusually hot conditions are also being felt in countries including the UK and China.
A warmer atmosphere can hold more moisture, making heavier storms more likely.
But hotter conditions can also pull more moisture out of the ground into the atmosphere, increasing the risk of droughts and wildfires.
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