Last month was the warmest May ever measured on Earth in 134 years, the National Oceanic and Atmospheric Administration (NOAA) announced June 23.
The record warmth comes from a combination of global warming and a natural climate pattern in the Pacific Ocean called El Niño, scientists think.
Several regions around the world suffered record heat in May, while a few were colder than average, but NOAA looks at the planet's overall temperature to gauge global trends. The average combined land and ocean surface temperatures in May were 1.33 degrees Fahrenheit (0.74 degrees Celsius) higher than the 20th-century average of 58.6 F (14.8 C), NOAA said in a statement. The last time May temperatures dipped below the 58.6 F average was in 1976, according to NOAA. The last below-average month was in 1985.
May's toasty temperatures were boosted by record-setting surface heat in the tropical Pacific Ocean, NOAA said. The global sea surface temperatures during May jumped 1.06 F (0.59 C) above the 61.3 F (16.3 C) average, also a new May record. [Video: Watch 60 Years of Rising Temperatures]
This Pacific Ocean warmth is a feature of the vast El Niño climate event developing in this region. During an El Niño year, typical Pacific weather patterns reverse, with bathlike warm water replacing cold currents in the eastern equatorial Pacific Ocean.
This huge swath of warm water strongly points to an El Niño, a periodic climate swing that can shift global weather patterns, such as rainfall and drought. However, forecasters still haven't officially declared the "child" has arrived, because atmospheric signals still lag behind the ocean temperatures. The chances for an El Niño fully developing are now at 80 percent by fall, NOAA said.
Whether El Niño arrives sooner or later, as the Pacific's oceanic heat wave continues to pump warmth and moisture into the atmosphere, global temperatures will likely continue to rise this year, scientists think. The warmest years in the past decade featured El Niños, and the previous record for warm ocean temperatures in May was set in 1998, another El Niño year.
May's record warmth continues a long-term trend, NOAA said. The last 351 months have been warmer than average, and much of the planet was unusually hot in recent months. Here are some highlights from the NOAA report:
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