Geneva ? The year 2003, marked by a sweltering summer and drought across large swaths of the planet, was the third-hottest in nearly 150 years, the United Nations weather agency said Tuesday.

The World Meteorological Organization estimated the average surface temperature for the year to be 0.81 degrees Fahrenheit higher than the normal 25.2 degrees.

The agency said that warmer weather could not be attributed to any one cause but was part of a trend that global warming was likely to prolong.

The agency, which collects data from forecasters worldwide, said the three hottest years since accurate records began to be kept in 1861 have all been in the past six years. The hottest was 1998, when the average temperature was up 0.99 degrees.

“The rhythm of temperature increases is accelerating,” said WMO deputy secretary-general Michel Jarraud.

This summer, much of Europe was struck by a prolonged heat wave, with temperatures exceeding 104 degrees. The hot weather was blamed for the deaths of thousands, most in France, and devastating forest fires in several countries. It also accelerated the melting of Alpine glaciers, the WMO said.

India and Pakistan also were hit by a deadly heat wave in May and June, when 1,500 people died as temperatures soared above 122 degrees Fahrenheit. The western United States continued to suffer from drought, and wildfires in California burned nearly 75,000 acres of land in October.

Over the 2002-03 winter, North America received its 10th-lowest recorded snowfall, although the northeastern United States was battered by a record snowstorm in February, the agency said.

Other parts of the world also faced extreme winter weather. January temperatures in northeastern Russia dropped to -49 degrees, while Mongolia also was gripped by an exceptionally harsh winter for the third year running, devastating livestock.

“You cannot attribute this to any single cause,” Jarraud said. “It’s about the very complex interaction between all the elements that make up the very complex machine that is the Earth.”

In the Atlantic Ocean, 16 separate storms developed this year, well above the 1948-96 average of 9.8.

Hurricane Isabel, which battered North Carolina, was one of the strongest on record. Hurricane Fabian was the most destructive to hit Bermuda in 75 years.

“By definition, exceptional events are exceptional, so they don’t occur very often. But global warming is likely to lead to more frequent extraordinary events and greater intensity of these events,” Jarraud said.