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September’s Unprecedented Heat, in 2 Eye-Popping Charts

Will September be the most abnormally hot month ever?

Emily Pontecorvo •
09/25/2023
The Blue Ridge Mountains.
Heatmap Illustration/Getty Images

By the end of August, scientists were already beginning to predict that 2023 would be the hottest year on record. June, July, and August had been the hottest consecutive summer months of all time. And then September happened.

Last week, Berkeley Earth climate scientist Zeke Hausfather took a look at daily global average temperature data for September and made a startling observation. It was on track to be the most anomalously hot month on record, period.

On September 17, as tens of thousands of climate activists took to the streets in Midtown Manhattan to demand an end to fossil fuels, the global average temperature was surging. The mercury rose to more than 1.8 degrees Fahrenheit above the average temperatures registered between 1991 and 2020. And those recent three decades were already unusually hot relative to pre-industrial temperatures. Compared to pre-industrial times, the day was 3.4 to 3.6 degrees hotter.

Numbers like this always sound laughably small, but when you take a look at the chart below, it's clear how exceptionally, worryingly hot this month has been.

Daily temperature anomaly chart.Daily global surface temperature anomalies in JRA-55 between 1958 and 2023, relative to the 1991-2020 baseline period used by the dataset.Courtesy of Zeke Hausfather / The Climate Brink

The lines represent daily temperature anomalies, or the difference between the temperature on a given day and the average temperature between 1991-2020 on that day. The red line shows temperature anomalies in 2016, the prior hottest year on record. The black line shows 2023, with September highlighted in blue. (The data comes from an analysis tool by the Japanese Meteorological Agency.)

Here’s the same data, but displayed in our favorite form of visualization, the *heatmap.* While global warming has clearly been ramping up in the last decade, September 2023 jumps off the map for sustained high temperatures.

Daily temperature anomaly heatmap.Heatmap of daily global mean surface temperature anomalies back to 1958 relative to the 1991-2020 baseline period.Courtesy of Zeke Hausfather / The Climate Brink

“It’s hard to overstate just how exceptionally high global temperatures are at the moment. They have blown past anything we’ve previously experienced by a huge margin,” Hausfather wrote on X this morning. He has more charts and information contextualizing the data over on the Substack he co-writes with Texas A&M professor Andrew Dessler, The Climate Brink.

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Emily Pontecorvo profile image

Emily Pontecorvo

Emily is a founding staff writer at Heatmap. Previously she was a staff writer at the nonprofit climate journalism outlet Grist, where she covered all aspects of decarbonization, from clean energy to electrified buildings to carbon dioxide removal.

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Sparks

The Country’s Largest Power Markets Are Getting More Gas

Three companies are joining forces to add at least a gigawatt of new generation by 2029. The question is whether they can actually do it.

Matthew Zeitlin •
02/26/2025
Natural gas pipelines.
Heatmap Illustration/Getty Images

Two of the biggest electricity markets in the country — the 13-state PJM Interconnection, which spans the Mid-Atlantic and the Midwest, and ERCOT, which covers nearly all of Texas — want more natural gas. Both are projecting immense increases in electricity demand thanks to data centers and electrification. And both have had bouts of market weirdness and dysfunction, with ERCOT experiencing spiky prices and even blackouts during extreme weather and PJM making enormous payouts largely to gas and coal operators to lock in their “capacity,” i.e. their ability to provide power when most needed.

Now a trio of companies, including the independent power producer NRG, the turbine manufacturer GE Vernova, and a subsidiary of the construction firm Kiewit Corporation, are teaming up with a plan to bring gas-powered plants to PJM and ERCOT, the companies announced today.

The three companies said that the new joint venture “will work to advance four projects totaling over 5 gigawatts” of natural gas combined cycle plants to the two power markets, with over a gigawatt coming by 2029. The companies said that they could eventually build 10 to 15 gigawatts “and expand to other areas across the U.S.”

So far, PJM and Texas’ call for new gas has been more widely heard than answered. The power producer Calpine said last year that it would look into developing more gas in PJM, but actual investment announcements have been scarce, although at least one gas plant scheduled to close has said it would stay open.

So far, across the country, planned new additions to the grid are still overwhelmingly solar and battery storage, according to the Energy Information Administration, whose data shows some 63 gigawatts of planned capacity scheduled to be added this year, with more than half being solar and over 80% being storage.

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Sparks

An Emergency Trump-Coded Appeal to Save the Hydrogen Tax Credit

Featuring China, fossil fuels, and data centers.

Emily Pontecorvo •
02/18/2025
The Capitol.
Heatmap Illustration/Getty Images

As Republicans in Congress go hunting for ways to slash spending to carry out President Trump’s agenda, more than 100 energy businesses, trade groups, and advocacy organizations sent a letter to key House and Senate leaders on Tuesday requesting that one particular line item be spared: the hydrogen tax credit.

The tax credit “will serve as a catalyst to propel the United States to global energy dominance,” the letter argues, “while advancing American competitiveness in energy technologies that our adversaries are actively pursuing.” The Fuel Cell and Hydrogen Energy Association organized the letter, which features signatures from the American Petroleum Institute, the U.S. Chamber of Commerce, the Clean Energy Buyers Association, and numerous hydrogen, industrial gas, and chemical companies, among many others. Three out of the seven regional clean hydrogen hubs — the Mid-Atlantic, Heartland, and Pacific Northwest hubs — are also listed.

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Why Your Car Insurance Bill Is Making Renewables More Expensive

Core inflation is up, meaning that interest rates are unlikely to go down anytime soon.

Matthew Zeitlin •
02/12/2025
Wind turbines being built.
Heatmap Illustration/Getty Images

The Fed on Wednesday issued a report showing substantial increases in the price of eggs, used cars, and auto insurance — data that could spell bad news for the renewables economy.

Though some of those factors had already been widely reported on, the overall rise in prices exceeded analysts’ expectations. With overall inflation still elevated — reaching an annual rate of 3%, while “core” inflation, stripping out food and energy, rose to 3.3%, after an unexpectedly sharp 0.4% jump in January alone — any prospect of substantial interest rate cuts from the Federal Reserve has dwindled even further.

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