As 12 months of record heat stacks up, scientists unpack the impacts around the globe

By Tyne Logan and Tom Saunders

Analysis - A new report by a team of international climate scientists shows the staggering amount of extreme heat days each country across the globe experienced last year, with the majority made more likely by human-induced climate change.

It comes as the world hits an alarming climate milestone, with data showing last month was the hottest May on record, marking what has now been 12 consecutive months of unprecedented global heat.

Australian National University professor Sarah Perkins-Kirkpatrick, who specialises in extreme heat, said it served as a stark "wake-up call" on how severe things were becoming.

"Last year was our hottest year on record and, to some extent, that was no surprise," Dr Perkins-Kirkpatrick said.

"But it's the fact that each month has stacked up on top of each other, and we've not had one month below the record, that has been quite surprising."

To better understand what has played out on the ground during those record months, a team of researchers from Climate Central, in collaboration with Red Cross Red Crescent Climate Centre and World Weather Attribution, analysed how many days of unusually hot weather each country experienced over the last year.

Extreme heat in 10 countries most affected by climate change*

Country	Days of extreme heat	Without climate change
Ecuador	179.6	10.1
Suriname	182.2	23.6
Panama	161.2	12.1
El Salvador	163.2	15.2
Singapore	147	0
Guyana	174.4	32.6
Colombia	155.3	15.9
Brunei	130.2	0
Gabon	137.6	11.7

Extreme heat in Pacific countries*

Country	Days of extreme heat	Without climate change
Solomon Islands	147	34.5
Papua New Guinea	136	24.6
Samoa	147.1	43.8
Fiji	108.5	25.6
Timor-Leste	111.2	37.2
Vanuatu	96.2	43.1
New Zealand	41.8	18.2
Australia	35.1	18.1

* Extreme heat days between 15 May, 2023 and 15 May, 2024 where temperatures exceeded the 90th percentile for each location compared to the 1991-2020 reference period.

Using real-time climate attribution methods, they were also able to say how many days were made more likely by climate change.

It found human-caused climate change added 26 more days of extreme heat, on average, across all places in the world, to what there would have been without a warmed planet.

In some places, nearly half the year was spent under unusually hot conditions, including parts of South and Central America, and south-east Asia.

In Ecuador, for example, the average person experienced 180 days of extreme heat above their local level during the past year, according to the analysis.

Without the influence of climate change, it found that number would have been 10.

Climate Central vice-president for science Andrew Pershing said the figures illustrated the "huge burden" the burning of fossil fuels imposed on people around the world.

"Different countries are each having their own story, and that's one of the things we tried to highlight in the report," Dr Pershing said.

"Australia didn't have a particularly interesting summer this year, but in Africa it's just day after day after day of climate change just beating down on that continent."

An extreme heat day is one that is warmer than 90 percent of all observed temperatures at the site from 1991-2020.

Dr Pershing said this was considered the point at which heat became particularly dangerous, with increases in temperature-related hospitalisations.

He said having the past 30 years as the baseline also meant the extreme heat was out of the ordinary even within the context of the climate people were used to.

While the report only looked at days of extreme heat, Dr Pershing said they had also seen the impact of global warming play out in intense rainfall and drought events.

In April, the desert city of Dubai recorded more than a year's worth of rainfall within 24 hours, flooding airport runways and motorways. And Mexico is currently in the grip of a severe heatwave.

How long will the record heat continue?

A look at the global air temperature over the past year shows just how easily records have been set, even when compared to our modern-day climate.

During the latest month, May, the average near-surface air temperature was 0.65 Celsius above the 1991-2020 baseline average, according to Copernicus's data, easily overtaking the previous record set in 2020.

When compared to pre-industrial levels (1850-1900), the month was 1.53C above average, breaching the Paris Agreement target of 1.5C for the 11th consecutive month.

And it is not just air temperatures that remain off the charts.

May 2024 also saw a continuation of record-warm global sea surface temperatures, extending the run of unprecedented oceanic heat to 14 months in a row - although sea ice around Antarctica has made a moderate recovery this year after record-low ice extent in 2023.

The hot May means the past 12 months are now also a record at 1.63C above pre-industrial levels, and ensures that, on its current trajectory, 2024 is now likely to surpass 2023 as the warmest year on record unless an unexpected rapid cooling occurs during the coming months.

While the recent global figures appear to indicate more than just a brief spike above the Paris mark, it is not likely to be permanent.

The recent tumbling of climate records is partly due to an injection of warmth from the recent El Niño, a pattern US National Ocean and Atmospheric Administration (NOAA) senior scientist Michael McPhaden is tracking.

"It takes time for the heat that is released from the ocean in the tropical Pacific to be distributed around the globe and show up as elevated global mean surface temperature," Dr McPhaden said.

"So there may be no relief in terms of global mean surface temperatures this calendar year.

"We may see it next year, as La Niña has had a chance to develop and take hold."

What's driving global heat?

Several factors have played into the Earth's record heat over the past year, some of which scientists are still trying to fully understand.

The onset of El Niño, in particular, has been flagged as one of the major year-to-year climate drivers that has helped boost global temperatures into record territory.

But climate scientists say by far the most significant contributor is rising greenhouse gas emissions, caused primarily by the burning of fossil fuels and deforestation, which have been responsible for approximately 1.1C of warming from 1850-1900 to 2021.

"The escalator and climate change go in only one direction and it's up, so don't be surprised when more records are set," Dr McPhaden said.

It has meant years of record heat have now become a frequent occurrence for the globe, while years of record cold are a rarity.

Each of the top 10 hottest years on record occurred in the past decade, while the coldest 10 on record all occurred more than 100 years ago - something Dr Perkins-Kirkpatrick points out should not happen.

"In a stable climate, record-hot years and record-cold years should statistically be occurring with the same probability, but that's not what's happening," she said.

"So the fact that these heat events just keep on being broken - they light up like Christmas trees every year - is just showing the underlying stress the global climate is in."

Adapting to a new climate reality

The latest line of heat records has been met with a response that climate scientists have made many times before. They say to stop records from tumbling the world needs to stop burning coal, oil, and natural gas.

"It's a, 'No shit Sherlock,' moment," Dr Perkins Kirkpatrick said.

"These records will continue to be broken for some time, particularly if we don't reduce our emissions quickly."

But Dr Perkins-Kirkpatrick said it had now reached a point where adaption to heat extremes was also necessary.

"We need to be really realistic and pragmatic of what we can achieve and in the time frame that we can achieve it," she said.

"So we must also be looking at adaptation more seriously than we ever have before.

"And the longer we leave that, the worse that becomes."

To this end, Dr Pershing said while record hot months and years would not stop in a stable climate, their danger would become more manageable.

"Once we get to zero emissions, many parts of the climate system will stabilise within a few years, and temperature is one of them," he said.

"That's the thing to me that's really interesting, is that it's something we can then get used to.

"Then we can say, 'This is the main temperature of our city, this is the infrastructure we need,' rather than, 'This is our temperature,' and then, 'Oh heck, it's even warmer, and we have to change even more.'

"A more stable environment gives ourselves the opportunity to adapt and adjust."

- This story was first published by the ABC