NOAA climate monitoring chief Deke Arndt said it may be worth studying why September, more than other months, keeps setting world records. It might be the lengthening of the Northern Hemisphere summer as a result of man-made global warming and continual loss of Arctic sea ice, which indirectly helps cool other parts of the world, said University of Victoria climate scientist Andrew Weaver.
This is the 16th time that the world has set or tied a record for hot temperature since 2000, according to NOAA. The last time the world set a cold temperature record was in December 1916, nearly 96 years ago.
These record-setting trends are manmade global warming at work, Weaver said.
"What's playing out is precisely what climate said we should expect to see 20 to 30 years ago," Weaver said.
For most of the year, world temperatures were warmer than normal, but not near record levels. At the same time, the United States kept setting heat records. But that reversed in September. It was a record hot month for the world, but the United States ranked only 23rd hottest.
Arndt said the heat was widespread but most intense in South America, Japan, Russia, Canada and the Atlantic Ocean.
Two weather factors may be in play, Weaver and Arndt said. The La Nina weather oscillation which is the flip side of El Nino and tends to depress global temperatures slightly ended. And the Arctic was unusually warm and had a record amount of sea ice melting, which are factors that alter weather throughout the Northern Hemisphere.
This is the 331st consecutive month with global temperatures above the 20th century average.
Some skeptics of global warming have been pointing to British data that a London newspaper claims show no warming since 1997. But the United Kingdom meteorological office and Weaver said the claims are misleading.
"I don't know what data they are looking at," Weaver said. "2010 is the warmest year. 2005 is the second warmest year."
NOAA September climate report > www.ncdc.noaa.gov/sotc/global/2012/9