Steamy September caps record-shattering summer — and scientists warn trend shows no sign of stopping

A European Union climate monitoring agency has found that last month was the hottest September ever recorded, coming in at 1.75 C above the pre–industrial average.

But more concerning is that 2023 is on track to become the hottest year on record for the planet.

“2023 has proven to be a very anomalous year,” said Samantha Burgess, deputy director of the EU’s Copernicus Climate Change Services (C3S). “We’ve had the warmest June, the warmest July and the warmest August on record. But September has really exceeded all of the previous broken records that we’ve seen over the last few months.

“When I speak to my colleagues around the world, no one has ever seen climate monitoring data like this.”

According to extensive data collected from satellites, weather stations, and ships and aircraft from around the world, September’s average air temperature was 0.93 C above the 1991–2020 average for the month, beating out the previous record set in 2020 by 0.5 C.

This comes just a week after the U.S. National Snow and Ice Data Center reported that this year’s minimum extent of sea ice in the Arctic was the fifth-lowest on record, and the Antarctic maximum sea ice extent was the lowest.

With so many record-setting months, the year-to-date global mean temperature is 1.4 C higher than the pre–industrial average.

The heat was felt around the world this summer. Phoenix, Ariz., experienced a record-breaking 31 consecutive days where temperatures were 43.3 C or higher, beating out the previous record of 18 days set in 1974. Nighttime temperatures didn’t bring any relief, often staying above 32 C.

In July, a township in China reached a record temperature of 52.2 C.

Canada wasn’t spared from the hot weather, either.

“We had the warmest summer [in Canada]. It didn’t even come close to the previous warmest in spite of the fact that we had kind of cooler temperatures in Montreal, Ottawa and Toronto,” said Dave Phillips, senior climatologist at Environment and Climate Change Canada.

While those cities experienced near-average temperatures for much of the year, that hasn’t been the case this week, as temperatures in those same cities neared 30 C — nearly twice the average for this time of year.

Looking toward 2024

The last nine years have been the nine warmest on record, with 2016 as the warmest ever. This despite the fact that the El Niño-Southern Oscillation weather pattern — a recurring natural phenomenon in the Pacific Ocean — had been in a cooling phase, known as La Niña, for three years.

Currently, we are experiencing El Niño conditions — a cyclical warming of ocean surface temperatures in the same area of the Pacific. This phase can cause a rise in global temperatures.

Though this El Niño only began in July, the U.S. National Oceanic and Atmospheric Administration is predicting that it will last through the winter and into the spring.

Because of that, 2024 is expected to be even warmer than 2023, Burgess said. But just how warm isn’t clear.

“We also know that this El Niño is starting in a warmer ocean with a warmer atmosphere than we’ve ever had in the past,” Burgess said. “So we’re flying a little bit blind in terms of … how strong this particular event will be.”

Michael E. Mann, a climatologist who popularized the “hockey stick” graph that illustrated rapid global warming, said he’s not surprised by the trend.

“A number of years ago we published a study that showed that we should expect this streak of record-breaking years to continue as long as we continue to generate carbon pollution,” he said in an email.

But Mann — whose recent book, Our Fragile Moment, addresses how climate has shaped humanity and how we can move forward — stressed that not all is lost.

“There’s no evidence we’re due for runaway warming,” he said. “The warming is steady and will continue as long as carbon emissions continue.

“The good news is that when carbon emissions reach zero, the warming of the surface of the planet ends almost immediately, so there is a direct and immediate impact of our efforts to decarbonize our economy.”

Burgess said these recent findings should be the impetus for change ahead of this year’s COP 28 climate conference.

“The climate crisis is here, is impacting all of us now, and we really need ambitious action,” she said.