July 3 was the world’s hottest day ever, U.S. scientists say

The entire planet sweltered to the unofficial hottest day in human recordkeeping July 3, according to University of Maine scientists at the Climate Reanalyzer project.

High temperature records were surpassed July 3 and 4 in Quebec and northwestern Canada and Peru. Cities across the U.S. from Medford, Oregon to Tampa, Florida have been hovering at all-time highs, said Zack Taylor, a meteorologist with the National Weather Service. Beijing reported nine straight days last week when the temperature exceeded 35 C (95 F).

This global record is preliminary, pending approval from gold-standard climate measurement entities like the National Oceanic and Atmospheric Association. But it is an indication that climate change is reaching into uncharted territory.

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It legitimately captures global-scale heating and NOAA will take these figures into consideration when it does its official record calculations, said Deke Arndt, director of the National Center for Environmental Information, a division of NOAA.

“In the climate assessment community, I don’t think we’d assign the kind of gravitas to a single day observation as we would a month or a year,’’ Arndt said. Scientists generally use much longer measurements — months, years, decades — to track the Earth’s warming. In addition, this preliminary record for the hottest day is based on data that only goes back to 1979, the start of satellite record-keeping, whereas NOAA’s data goes back to 1880.

But Arndt added that we wouldn’t be seeing anywhere near record-warm days unless we were in “a warm piece of what will likely be a very warm era” driven by greenhouse gas emissions and the onset of a “robust” El Nino. An El Nino is a temporary natural warming of parts of the central Pacific Ocean that changes weather worldwide and generally makes the planet hotter.

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Human-caused climate change is like an upward escalator for global temperatures, and El Nino is like jumping up while standing on that escalator, Arndt said.

The global daily average temperature for July 3 came in at 17.01 degrees Celsius or 62.6 degrees Fahrenheit, according to the University of Maine’s Climate Reanalyzer, a common tool often used by climate scientists for a good glimpse of the world’s condition. The reanalyzer is based on a NOAA computer simulation intended for forecasts that uses satellite data. It is not based on reported observations from the ground. So this unofficial record is effectively using a weather tool that is designed for forecasts, not record-keeping.

This average temperature may not seem that hot, but it’s the first time in the 44 years of this dataset that the temperature surpassed the 17-degree Celsius mark.

Hotter global average temperatures translate into brutal conditions for people all over the world. In the U.S., heat advisories are in effect this week for more than 30 million people in places including portions of western Oregon, inland far northern California, central New Mexico, Texas, Florida and the coastal Carolinas, according to the National Weather Service Weather Prediction Center. Excessive heat warnings are continuing across southern Arizona and California, they said.

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When the heat spikes, humans suffer health effects.

“Those hotter temperatures that happen when we get hotter than normal conditions? People aren’t used to that. Their bodies aren’t used to that,” said Erinanne Saffell, the Arizona state climatologist and an expert in extreme weather and climate events.

Saffell added that the risk is already high for the young and old, who are vulnerable to heat even under normal conditions.

“That’s important to understand who might be at risk, making sure people are hydrated, they’re staying cool, and they’re not exerting themselves outside and taking care of those folks around you who might be at risk as well,” she said.