ARI SHAPIRO, HOST:
When you look at global temperatures, July was the hottest month on average since reliable recordkeeping started, and July was not a freak occurrence. The past 10 years have seen many high temperature records broken. NPR's Christopher Joyce explains what's going on.
CHRISTOPHER JOYCE, BYLINE: When scientists tallied up the temperature readings from around the world last month, this is what they discovered.
JAKE CROUCH: July 2016 was the warmest month we have observed in our period of record that dates back to 1880.
JOYCE: Jake Crouch is a climate scientist at the National Oceanic and Atmospheric Administration. The temperature record is an average. Some places were a bit cooler than normal, Siberia, for example. Other places were mind-bogglingly hot.
CROUCH: A temperature in Kuwait on July 22 reached 126.5 degrees Fahrenheit, according to an observation taken by the United States Air Force.
JOYCE: July's average temperature was a big jump from what was typical in the 20th century. This year, it was 1.5 degrees Fahrenheit warmer. And the U.S. has by and large sizzled along with the rest of the world.
CROUCH: We can see that almost the entire contiguous U.S. was warmer than average for 2016 so far, with a lot of that warmth situated across the northern tier and in the West.
JOYCE: Scientists at NOAA and NASA agree that climate change is part of the reason for this, but this year, much of the world experienced an El Nino. That's an occasional weather pattern that starts in the Pacific and spreads warm air over large parts of the world. El Nino added some heat, but it was pretty much over in June. Crouch says weather data predict continued record heat.
CROUCH: 2016 is very likely to be the warmest year on record for the globe.
JOYCE: All that heat has worsened the drought in California and the Southwest. The dry conditions have caused a busy wildfire season, and the peak time for Western fire - September - is yet to come. Even without fire, the high temperatures draw moisture out of the ground and are damaging and killing trees in the West.
But no place is cooking quite like the Arctic. It's been warming at twice the rate of the rest of the world. Arctic scientist Walt Meier at NASA's Goddard Space Flight Center in Maryland says things have changed drastically over the past 20 years, especially with sea ice.
WALT MEIER: It's melting earlier. The ice is thinner, so it gets pushed around by the winds more. It's more broken up. It used to be kind of - more of a big sheet of ice, and now it's chunks of ice. It's kind of like going from like a big ice cube to kind of crushed ice.
JOYCE: The Arctic ice this year has shrunk almost as much as it did in 2012, and that was the most severe melting to date. Without sea ice in the summer to reflect sunlight back into space, the Arctic Ocean heats up. That melts yet more ice in a heating and melting loop that feeds on itself.
Oceanographers say an ice-free Arctic Ocean in summer is not far off, and that could affect the way currents circulate water around the Atlantic Ocean. And the warmer Arctic also affects atmosphere in the way that influences our weather.
MEIER: There's emerging evidence that the warming in the Arctic related to the loss of sea ice is causing a loopier, kinkier jet stream.
JOYCE: That's the jet stream that carries cold air and moisture from over the Pacific into the U.S. A warmer Arctic makes it less predictable. In short, Meier says, the Arctic is the northern hemisphere's refrigerator, and someone has left the door open. Christopher Joyce, NPR News.
NPR transcripts are created on a rush deadline by Verb8tm, Inc., an NPR contractor, and produced using a proprietary transcription process developed with NPR. This text may not be in its final form and may be updated or revised in the future. Accuracy and availability may vary. The authoritative record of NPR’s programming is the audio record.