This decade is on track to be the hottest on record, according to the UN's World Meteorological Organization, and 2009 is the fifth-warmest year on record.
Speaking on the sidelines of the climate conference, WMO head Michel Jarraud pointed to extreme hot spots this year - Australia had its third-warmest year since records began in 1850, "with three exceptional heat waves."
"I could go on. There was the worst drought in five decades which affected millions of people in China, a poor monsoon season in India causing severe droughts, massive food shortages associated with a big drought in Kenya," he said.
Mr. Jarraud also highlighted extreme floods, including one that broke a 90-year record in Burkina Faso. As well, 2009 marked the third-lowest summer Arctic sea ice on record, after the two previous years.
Vicky Pope, head of climate change advice at Britain's Met Office Hadley Centre, which supplied some of the WMO data, agreed that 2009 is likely to be the fifth-warmest year.
"Essentially what's happened is we've gone into an El Nino," she added, referring to a natural weather pattern which drives abnormal warming in the eastern Pacific Ocean and can unleash wider havoc in global weather.
If 2009 ends as the fifth-warmest year, it would replace 2003. According to the U.S. space agency NASA, the other warmest years since 1850 have been 1998, 2005, 2007 and 2006. NASA says the differences in readings among these years are so small as to be statistically insignificant.
The hottest year on record, 1998, coincided with a powerful El Nino, and a new El Nino developed this year.
"It's just a matter of years before we break the record," Mr. Jarraud said. "It's getting warmer and warmer. The warming trend is increasing."
"It's difficult to say [when the record will be broken]because of the variability. The first time there will be a strong El Nino the temperature will be greater than before."
Mr. Jarraud rejected a "climategate" row over leaked e-mails from Britain's University of East Anglia Climatic Research Unit that showed some scientists' efforts to boost the credibility of climate change at the expense of skeptics.
The WMO used British - including CRU - and two U.S. data sources for its temperature analysis. "The three separately show almost identical results," Mr. Jarraud said.
The fact that the record for the hottest year has not been broken since 1998 has helped fuel arguments from a small minority of scientists that climate change may not be as severe as feared.
But Ms. Pope said that temperatures had "climbed slightly" in the past decade. "There hasn't been a cooling [since the 1998 spike]" she said.
The decade 2000-2009 was 0.44 Celsius above the 1961-1990 average, Ms. Pope said, while the 1990s decade was 0.23C higher.
Reuters News Agency with a report from AP