This was the Northern Hemisphere's hottest summer ever

Earth has sweltered through its hottest Northern Hemisphere summer ever measured, with a record warm August capping a season of brutal and deadly temperatures, according to the World Meteorological Organization.

Last month was not only the hottest August scientists ever recorded by far with modern equipment, it was also the second hottest month measured, behind only July 2023, WMO and the European climate service Copernicus announced Wednesday.

August was about 1.5 degrees Celsius (2.7 degrees Fahrenheit) warmer than pre-industrial averages. That is the threshold that the world is trying not to pass, though scientists are more concerned about rises in temperatures over decades, not merely a blip over a month's time.

The world's oceans — more than 70% of the Earth's surface — were the hottest ever recorded, nearly 21 degrees Celsius (69.8 degrees Fahrenheit), and have set high temperature marks for three consecutive months, the WMO and Copernicus said.

“The dog days of summer are not just barking, they are biting,” United Nations Secretary-General Antonio Guterres said in a statement. “Climate breakdown has begun.”

So far, 2023 is the second hottest year on record, behind 2016, according to Copernicus.

Scientists blame ever warming human-caused climate change from the burning of coal, oil and natural gas with an extra push from a natural El Nino, which is a temporary warming of parts of the Pacific Ocean that changes weather worldwide. Usually an El Nino, which started earlier this year, adds extra heat to global temperatures but more so in its second year.

Climatologist Andrew Weaver said the numbers announced by WMO and Copernicus come as no surprise, bemoaning how governments have not appeared to take the issue of global warming seriously enough. He expressed concern that the public will just forget the issue when temperatures fall again.

“It’s time for global leaders to start telling the truth,” said Weaver, a professor at the School of Earth and Ocean Sciences at the University of Victoria in Canada. “We will not limit warming to 1.5 C; we will not limit warming to 2.0 C. It’s all hands on deck now to prevent 3.0 C global warming — a level of warming that will wreak havoc worldwide.”

Copernicus, a division of the European Union’s space program, has records going back to 1940, but in the United Kingdom and the United States, global records go back to the mid 1800s and those weather and science agencies are expected to soon report that the summer was a record-breaker.

“What we are observing, not only new extremes but the persistence of these record-breaking conditions, and the impacts these have on both people and planet, are a clear consequence of the warming of the climate system,” Copernicus Climate Change Service Director Carlo Buontempo said.

Scientists have used tree rings, ice cores and other proxies to estimate that temperatures are now warmer than they have been in about 120,000 years. The world has been warmer before, but that was prior to human civilization, seas were much higher and the poles were not icy.

So far, daily September temperatures are higher than what has been recorded before for this time of year, according to the University of Maine's Climate Reanalyzer.

While the world's air and oceans were setting records for heat, Antarctica continued to set records for low amounts of sea ice, the WMO said.

“Antarctic sea ice extent was literally off the charts, and the global sea surface temperature was once again at a new record,” WMO's secretary-general, Petteri Taalas, said in a statement released to the media. "It is worth noting that this is happening BEFORE we see the full warming impact of the El Nino event, which typically plays out in the second year after it develops.”

Borenstein reported from Washington.

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