The current year was also the most expensive for the insurance industry in coping worldwide with hurricanes, typhoons and other weather-related natural disasters, according to new figures released by U.N. environmental officials.
The World Meteorological Organization said it expects Earth's average surface temperature to rise 0.8 degrees above the normal 57 degrees Fahrenheit, adding 2004 to a recent pattern that included the hottest year registered in 1998 and the next three warmest since then.
The month of October also registered as the warmest October since accurate readings began in 1861, said the agency, which is responsible for assembling data from meteorologists and climatologists worldwide.
"This was a very warm year," said Michel Jarraud, the World Meteorological Organization secretary-general.
The report's release comes as environmental ministers from some 80 countries gathered in Buenos Aires for a United Nations conference on climate change, looking at ways to cut down on greenhouse gases that some say contribute heavily to Earth's warming.
This summer, heat waves in southern Europe pushed temperatures to near-record highs in southern Spain, Portugal and Romania, where thermostats peaked at 104 degrees while the rest of Europe sweltered through above-average temperatures.
Jarraud said the warming and increased storm activity could not be attributed to any particular cause, but was part of a global warming trend that was likely to continue.
Scientists have reported that temperatures across the globe rose an average of 1 degree over the past century with the rate of change since 1976 at roughly three times that over the past 100 years.
This year, the Caribbean had four hurricanes that reached Category 4 or 5 status - those capable of causing extreme and catastrophic damage. It was only the fourth time in recent history that so many were recorded. The hurricanes of 2004 caused more than $43 billion in damages in the Caribbean and the United States.
The worst damage was on Haiti, where as many as 1,900 people died from flooding and mudslides caused by Tropical Storm Jeanne in September.
Japan and the Philippines also saw increased extreme tropical weather, with deadly typhoons lashing both islands. Japan registered a record number of typhoons making landfall this year with 10, while back-to-back storms in the Philippines killed at least 740 people in the wettest year there since 2000, the U.N. agency said.
Statistics released at the climate change conference showed that natural disasters across the world in the first 10 months of the year cost the insurance industry just over $35 billion, up from $16 billion in 2003.
Munich Re, one of the world's biggest insurance companies, said the United States tallied the highest losses at more than $26 billion, while small developing nations such as the Caribbean islands of Grenada and Grand Cayman were also hit hard.
Other parts of the world also witnessed extreme weather, with droughts occurring in the western United States, parts of Africa, Afghanistan, Australia and India. Jarraud, of the U.N. weather agency, said the droughts were part of what appears to be a surge over the last decade.
The prolonged rising temperatures and deadly storms were matched by harsh winters in other regions.
Peru, Chile, and southern Argentina were all hit with severe cold and snow during June and July.
Jarraud said the high temperatures like those seen in parts of Europe this year were expected to inch up in the coming years.
Citing recent studies by European climatologists, Jarraud said heat waves in Europe "could over the next 50 years become four or five times as frequent as they are now."
By Kevin Gray