The global temperature was 0.63 degree C (1.1 degree F) above the mean going back to 1880, when the first reliable instrument recordings were available, said the National Oceanic and Atmospheric Administration, part of the US Commerce Department.

Earth's second-hottest month was September 2003, but September 2005 was only the fourth-hottest month ever for the United States, NOAA said.

This year, the US state of Louisiana, where New Orleans in located, had its hottest September in 111 years. The US Gulf Coast was battered by the first of two hurricanes on August 29, during a particularly active tropical storm season.

NOAA and other meteorologists follow the temperatures of tropical waters closely, because the strength of tropical storms is related to the temperatures of the waters of the Atlantic, Caribbean and the Gulf of Mexico.

On September 28, the National Snow and Ice Data Center (NSIDC) reported shrinkage of the Arctic ice cap for the fourth consecutive year, as evidence of global climate change.

"Considering the record low amounts of sea ice this year leading up to the month of September, 2005 will almost certainly surpass 2002 as the lowest amount of ice cover in more than a century," said Julienne Stroeve of NSIDC.

"If current rates of decline in sea ice continue, the summertime Arctic could be completely ice-free well before the end of this century," she said.