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World registers hottest day ever recorded; what’s to come?

ASU meteorologist says future generations may 'live in a different world'


Child running through sprinklers outside.

Photo courtesy of Unsplash

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July 11, 2023

Editor’s note: This story is featured in the 2023 year in review.

On Monday, July 3, the hottest day ever was recorded globally, according to data from the U.S. National Centers for Environmental Prediction. 

Since then, three more global temperature records have been set or tied, along with seven days of global average temperatures soaring to 62.6 degrees Fahrenheit, or 17 Celsius, which has not occurred since at least 1940 when recordkeeping began.

There is little doubt that the world’s climate is changing, but what is causing this sudden increase in global temperatures this summer, and what do current trends of extreme heat tell us about what is to come? 

ASU News spoke to Randy Cerveny, the keeper of the world’s records of weather for the World Meteorological Organization (WMO) and a President’s Professor in ASU’s School of Geographical Sciences and Urban Planning, to learn more about trends of extreme heat, the consequences of record-breaking temperatures and what the future may look like if current trends aren’t stalled or reversed. 

ASU President's Professor Randy Cerveny. Photo by Deanna Dent/Arizona State University

Note: This interview has been edited lightly for clarity and brevity.

Question: Reports have headlines saying that “the planet saw its hottest day on record last week” and more records may follow; is that accurate? 

Answer:  That is a strange way of phrasing it, but it is correct. To me, the phrase "hottest day on record" implies that every place on Earth was hot — no, it doesn’t work that way. That number by the U.S. National Centers for Environmental Information is a geographically weighted average of all temperatures around the planet. What they are saying is that the average of all temperatures, weighted by the area they represent, was the highest value we have recorded.

I personally would say, "the temperature of the Earth, as averaged from our existing set of sensors, was the highest or hottest temperature recorded."

Q:  What is causing this sudden increase in temperature?

A: Two things are causing it. Long term, it’s the underlying steady year-by-year increase in temperatures around the world due to our human activities over the last hundred years; and short term, it’s the start of an El Niño episode in the Pacific Ocean. El Niño is a massive warming of the central equatorial Pacific Ocean. Since the Pacific Ocean covers such a large part of the planet, when that ocean warms, the entire planet’s average temperature increases.

Q: How does the process of certifying temperature records work, and why do certifiers not use the global average metric?

A: We at the WMO Archive of Weather and Climate Extremes work with individual stations — not with aggregated values for large regions or the globe. The reason is that aggregated temperature value is a function of mathematical relationships linking temperatures to geographical measurements. 

For example, is the Phoenix Sky Harbor temperature representative of just the airport? Or just Phoenix? Or just Maricopa County? Or of Arizona? How we average temperatures across space is a very complex mathematical process. The people at (the National Centers for Environmental Information) are experts at that type of thing. We at the WMO Archive work only with instrumented observations for specific locations.

Q: What do the data and records from the past few years indicate about the overall temperature trends?

A: We are getting warmer. The last three years haven’t had record-high global temperatures, although they have remained very high, because of the occurrence of three years of La Niña — the cooling of the Pacific. Now with El Niño, we will really see global temperatures rise.

Q: Could you discuss the potential consequences of these record-breaking temperatures? What kind of impact might we expect to see in terms of heat waves and other climate changes?

A: The three common effects attributed to anthropogenic climate change are increased rainfalls, particularly as associated with tropical cyclones, increased droughts and much warmer nights. 

Q: What is the important takeaway message for someone who’s been reading the news and seeing these global records fall?  

A: This finding announced by the National Centers for Environmental Information continues to demonstrate that our Earth is continuing to warm, and we — humanity — are one of the primary causes of those increases in temperatures.  

Our available scientific research continues to indicate that increasing warmth will cause fundamental changes in the lives of our children and grandchildren. Unless the current climate trends slow or reverse, they will live in a different world than the one in which we have lived.

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