A decades-long global warming trend that most climate experts say is linked to rising levels of heat-trapping smokestack and tailpipe gases continued apace this year, according to summaries issued yesterday by several national and international climate agencies. Figures differed slightly, with British weather officials and the World Meteorological Organization, based in Geneva, estimating that 2006 would end up the sixth warmest year since modern records began and NASA scientists putting it fifth.

But all of the reports noted that temperatures greatly above normal were recorded in places as varied as Australia and Scandinavia’s Arctic islands, shattering a variety of longstanding records. The global climate has warmed and cooled naturally throughout Earth’s history, including a protracted warm spell a millennium ago and a “little ice age” from the 1400s through the 1700s.

But the last 50 years of warming, many climate scientists say, is pressing beyond natural peaks of the last 11,000 years. They say the changes cannot be explained without including a substantial, and growing, push from billions of tons of annual emissions of carbon dioxide and other gases known to trap heat in the air.

The records set this year support various studies that “showed links between human behavior and the warming trend,” said David Parker, a climate scientist at Britain’s Met Office. England recorded its warmest average annual temperature, 51.5 degrees Fahrenheit, since the Central England Temperature series began in 1659, British officials said. The contiguous United States had its third warmest year since records began in 1880, according to the analyses. Blistering summer heat contributed to the worst fire season on record, with more than 9.5 million acres burned through early December.

Scientists at NASA’s Goddard Institute for Space Studies said that the Earth’s five warmest years since the late 1880s were, in decreasing order, 2005, 1998, 2002, 2003 and — if no unexpected fluctuations occur the rest of this month — 2006. James E. Hansen, the director of the Goddard center, said that 2007 was likely to be warmer than this year because one of the periodic hot spells in the tropical Pacific Ocean, called El Niño, has begun and should persist into next spring.

In February, the Intergovernmental Panel on Climate Change will release the main findings of its first update since 2000 on causes of global warming. The previous report concluded that most of the warming since 1950 was probably caused by human activities.

Research and fresh computer simulations considered under the new review have greatly strengthened that link, while also closing in on a possible warming of 5 degrees above the 1990 average, more or less, should the concentration of carbon dioxide double from the longstanding peak measured before the industrial era.

For at least 600,000 years before the Industrial Revolution, the concentration of carbon dioxide rarely nudged beyond 280 parts per million. It is now 382 parts per million and rising steadily. Without a worldwide shift to nonpolluting energy technologies, such a doubling is considered almost unavoidable given the growth in such emissions in both wealthy and developing countries, but particularly in China and India.
(By Andrew C. Revkin, New York Times, 15/12/2006)