Even Climate Scientists Are Surprised by How Hot It's Gotten

Scientists who've spent careers predicting how hot the planet would get are now watching it outpace their own models.

Record-breaking heat waves across Europe and North America this year are stunning even the researchers who study climate change professionally, with a still-unresolved 2023 temperature anomaly underscoring genuine gaps in current understanding.

The Anomaly Nobody Can Fully Explain

In September 2023, global monthly average temperatures overshot the previous record by 0.5°C, the largest such margin ever recorded and extreme even accounting for that year's El Niño.

Scientists have investigated several possible causes, including water vapor from a 2022 volcanic eruption, a drop in atmosphere-cooling air pollution from the shipping industry, declining cloud cover, and natural climate variability.

None of those factors, individually or combined, fully accounts for the size of the 2023 surge, leaving it as an open question researchers are still actively studying.

What's Driving This Year's Heat

A rapid scientific study of Europe's most recent heat wave found it was not only the continent's worst on record, but that the extreme temperatures would have been "virtually impossible" a few decades ago before human-caused warming intensified.

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Kim Cobb, a climate scientist at Brown University, said the primary driver behind rising deadly heat waves worldwide is fossil fuel burning, since a modest baseline of warming produces an exponential increase in extreme heat events.

Michael Mann, a climate scientist at the University of Pennsylvania, said record sea surface temperatures — driven partly by El Niño and partly by longer-term warming — fuel more extreme weather because warmer oceans hold more moisture available to intensify storms and heavy rainfall.

The Current North American Heat Wave

Temperature records have been tied or broken in multiple major US and Canadian cities this year, with 106°F (41°C) recorded in Atlantic City, New Jersey, on 4 July.

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As of 5 July, 25 deaths had been attributed to this heat wave, which overlapped with the FIFA World Cup, US Independence Day and Canada Day celebrations.

In Canada, extreme heat triggered large thunderstorms on Canada Day itself, contributing to widespread flooding and leaving thousands of homes without power, with roughly 50,000 Hydro-Québec customers still without electricity the following morning.

Why El Niño Complicates the Picture

Columbia University climate scientist Michael Tippett said there's typically no strong average link between El Niño and shifts in US and European summer weather, since El Niño's influence is usually stronger in fall and winter.

Cobb noted this particular El Niño is unusual in multiple respects, meaning its impact could differ meaningfully from past events even without a clear historical pattern to rely on.

Nearly half of the United States, roughly 180 million people, was placed under a "major" or "extreme" heat risk designation by the National Weather Service starting 28 June.

TL;DR

• Climate scientists say recent heat waves have exceeded what their own models predicted.

• A 0.5°C global temperature anomaly in September 2023 remains only partially explained.

• The current North American heat wave has caused 25 deaths and broken multiple city temperature records.

• Roughly 180 million Americans were placed under major or extreme heat risk warnings.

• Scientists agree fossil fuel-driven warming is the primary driver of increasingly severe heat waves.

Read More

• El Niño Watch Returns as Climate Agencies Warn of Extreme Weather Risks

• Dangerous Heat Dome to Grip US Through July 4 Weekend

• Extreme Heat Watch Expands Across the US — Why Officials Are Warning Millions