Last month was among Earth’s warmest Junes ever recorded, according to data released by NASA and the National Oceanic and Atmospheric Administration.
NASA’s assessment differs slightly from a report out Thursday from NOAA, which also keeps a global temperature data set that uses somewhat different methods. NOAA concluded that last month was Earth’s six-warmest June on record, also dating to 1880.
Much of the difference probably lies in the two data sets’ treatment of the polar regions, experts with NASA and NOAA said. At present, the NASA data set contains more inputs from the Arctic and Antarctic, the latter of which showed very high temperatures in June. But both data sets show that the globe has warmed dramatically, especially since around 1980.
“Even though we’re ranking slightly different, we’re still saying the same story here,” said Ahira Sánchez-Lugo, a scientist with NOAA’s National Centers for Environmental Information (NCEI) who is lead author of the agency’s Global Climate Report.
Both agencies use about 10,000 land-based temperature stations around the globe — in addition to a large array of ocean measurements — to calculate the global average temperature.
Sánchez-Lugo said warming was particularly dramatic last month in parts of Europe and Asia. She noted that while summer months always feature heat waves, “we’re seeing these types of heat waves occur more intensely and more frequently.”
Also, while we tend to think of summer as featuring the longest days of the year and the most sunshine, Sánchez-Lugo said nighttime temperatures also are rising.
“During nighttime, we’re supposed to be able to cool off. Not only us, but animals, crops, everything,” Sánchez-Lugo said. “When that doesn’t happen, then that’s when we get heat exhaustion, or heat disease, because the nighttimes are not cooling as they used to.”
Scientists emphasize that the real message lies in the totality of the data, not the data for just one month.
“The key metrics for global warming are the long-term trends, and this month’s anomalies are in line with that increasing trend,” said Gavin Schmidt, who heads NASA’s Goddard Institute for Space Studies, which produces the data set in question.
“The exact rankings for any month are subject to more uncertainty, and while they may get attention, it’s the underlying trend that matters.”