CANCUN, Mexico (Reuters) - This year is on course to be among the top three warmest since records began in 1850, and the past decade was the warmest, in a new sign of man-made climate change, the United Nations said on Thursday. This year so far was slightly warmer than both 1998 and 2005, the previous top two, but could slip if December is a cool month, the UNs World Meteorological Organization (WMO) said in a report issued on the sidelines of UN climate talks in Mexico. The trend is of very significant warming, WMO head Michel Jarraud told a news conference. Asked if the data were new evidence that emissions of greenhouse gases were warming the climate, he said: Short answer: yes. These are the facts. If nothing is done ... (temperatures) will go up and up, he said, saying that the findings would guide negotiators meeting in Cancun from November 29 to December 10. The WMO said that land and sea surface temperatures so far in 2010 were 0.55 degree Celsius (1 F) above a 1961-1990 average of 14 degrees Celsius (57.2 degrees F). The years 2001-10 were the warmest decade, it said. The WMO said that warming has been especially strong in Africa, parts of Asia and parts of the Arctic. Pakistan recorded a record temperature of 53.5 degrees Celsius (128.30 F), the warmest in Asia since 1942. The findings, which confirmed a report by Reuters last week, coincided with a cold snap across northern Europe, where heavy snow caused travel chaos. Jarraud cautioned against using local temperatures to judge global trends. There is a significant possibility that 2010 could be the warmest year, he said. A final ranking for 2010 is due to be published early in 2011. Jarraud said that one years temperature could be influenced by natural variations and that the decade-long trends were most relevant to negotiators in Cancun seeking to avert more floods, droughts, desertification and rising sea levels. The British Met Office, one of the three main groups compiling worldwide data, also said 2010 was more likely than not the warmest year, ahead of 1998.