Just how hot was July? Hotter than anything on record

Human-driven climate change pushed global temperatures to never-before-seen heights in July, according to new data from the National Oceanic and Atmospheric Administration and NASA. The month is now officially the hottest July on record since record-taking began in the 1800s.

And it wasn't even close: the month was a whopping 0.4 °F warmer than the previous record set in 2019, and well over 2.1 °F hotter than the 20th century average.

"Most records are set in terms of global temperature by a few hundredths of a degree," says Russell Vose, a climate expert at NOAA's National Centers for Environmental Information. But this one, nearly half a degree Fahrenheit, was "bigger than any other jump we've seen."

That was not what Vose expected to see. "I am rarely surprised, that's what my friends tell me. And I was surprised by this number."

The intensity of July's heat is certainly exceptional, says Sarah Kapnick, chief scientist and climate expert at NOAA who worked on the report. It's also part of a long, clear pattern of planetary warming going back decades, driven primarily by humans burning fossil fuels. It's only likely to get hotter. "The next few years will be the coolest of my life if the world continues to emit greenhouse gasses," Kapnick says.

July's record-breaking temperatures were not subtle. Intense heat waves gripped many regions of the world. In the U.S, Arizona, New Mexico, and Florida posted their hottest months ever since NOAA started taking records in 1880. Northwestern China experienced some of the hottest temperatures ever, topping 122°F. Unseasonably hot weather also settled in across the Southern Hemisphere; even in the depths of winter, temperatures exceeded 100°F in some parts of Chile and Argentina.

The oceans ran an equally high fever. Off the coast of Florida, temperatures at the sea surface topped 100°F. Alarmed scientists rushed to protect or move coral nurseries to deeper, cooler water. Some parts of the North Atlantic Ocean hovered 7 to 10°F above the long-term average. The central Atlantic, the birthing ground for hurricanes, also experienced off-the-charts heat, raising the risk of more intense storms this season.

"Oceans also are key factors for regulation of climate by soaking up heat," says Rajiv Chowdhury, a global health and climate expert at Florida International University, but "these useful impacts on land temperature become far less impactful when the oceans heat."

Many scientists were alarmed not only by the intensity of the heat but also how long it lasted. "That's what kills, the duration of heat," not just the heat itself, says Pope Moseley, an intensive care physician and heat expert at Arizona State University. When heat persists—especially if nights stay exceptionally warm as they did in many heat-stricken zones last month—people's bodies don't get a chance to cool down.

That unrelenting heat stress exacerbates health problems like heart disease and stroke risk. One study from Sweden found that heat deaths increase by two to four percent a day s hot weather extends.

Phoenix strung together 31 days of daytime temperatures that exceeded 110° F. The heat index, which takes both air temperature and the dangerous effects of humidity into account, topped 100° F for 46 days in Miami.

This year is shaping up to be one of the hottest years—and possibly the hottest ever—in recorded history. Next year could be even worse, says Gavin Schmidt, a climate scientist at NASA. An El Nino event, which raises planetary temperatures, is intensifying right now. "Not only is 2023 going to be an exceptionally warm and possibly a record year, but we anticipate that 2024 will be warmer still," he says.

Any one super-hot month, or even year, solidifies a clear pattern: a steady upward march of global temperatures over decades. The last nine years have been the hottest ever seen. Each of the last five decades has been hotter than the one before.

"A year like this gives us a glimpse at how rising temperatures and heavier rains can impact society and stress critical resources," says Kapnick. "These years will be cool by comparison by the middle of the century if we continue to warm our planet as greenhouse emissions continue."

There are glimmers of progress. Global demand for fossil fuels could be nearing its peak, according to a 2022 analysis from the International Energy Agency, while countries from the U.S. to China are adding renewable energy sources, like solar and wind, at an unprecedented clip. [Copyright 2023 NPR]