2011-02-03 / Features

Global Warming Waning?

2010 tied as warmest year on record
By Pete Spotts
CHRISTIAN SCIENCE MONITOR

Last year tied 2005 as the warmest year on record, federal climatologists said last Wednesday, adding that an analysis of the year’s data strengthened the notion that greenhouse gases from burning fossil fuels are continuing to warm Earth’s climate.

According to a preliminary analysis of year-end data released last Wednesday, the global average temperature in 2010 topped the 20th century average by 1.12 degrees Fahrenheit.

This caps a decade marked by nine of the 10 warmest years on record and represents the 34th consecutive year in which global average temperatures topped the 20th-century average, according to data compiled by the National Oceanic and Atmospheric Administration’s Climatic Data Center in Asheville, N.C.

In addition, the year was the wettest on record globally, although rain and snowfall varied widely from place to place.

A moderate-to-strong El Nino pattern in the eastern Pacific and a similarly energetic La Nina that followed played key roles in 2010 in setting up conditions that contributed both to temperature and precipitation patterns during the year.

The two patterns alternate over periods of two to seven years in the tropical Pacific. El Nino brings an expanse of warm water from the western Pacific to a region of the ocean off northern South America, while La Nina replaces the warm water with unusually cold water. These swings trigger changes in atmospheric circulation patterns that, while most prominent in the tropics, also affect circulation patters at higher latitudes as well.

But while these natural swings in Earth’s climate played important roles in shaping seasonal weather patterns, as well as the year’s global-temperature ranking, NOAA officials say, so has global warming – particularly over the past 30 to 40 years.

Climate has not stopped warming

“There has been some notion people have put forth that the climate stopped warming in about 2005. This year’s results show that notion lacks credibility,” said David Easterling, who heads the Climatic Data Center’s scientific services division. Instead, he says, the year-end analysis “reinforces the notion that we’re seeing an influence on the climate by greenhouse gases.”

That might seem counterintuitive to residents of the U.S. South, for instance, who are still thawing out from heavy snows. But researchers caution against confusing a seasonal storm with climate, which is a decade- to centuries long average of temperature, precipitation, and other atmospheric conditions.

“Climate change is a global phenomenon and a long-term phenomenon,” Dr. Easterling explains. Unusually cold temperatures, such as those the Eastern U.S. has experienced over the past two winters, merely reflect natural variations that are superimposed on the much-longer-term warming trend. Global climate – changing or relatively stable – encompasses much more in time and space than a winter Nor’easter burying New England under a foot or more of snow.

Data for 2010 also revealed a warm and wet year on average for the continental United States, according to the data center’s analysis.

Heavy snow in the East last February and record warmth in the summer along the southeast and into New England “were two fairly remarkable events,” said Derek Arndt, who heads the center’s climate monitoring branch.

Extra precipitation had benefits

Rain and snowfall over the U.S. in 2010 topped the longterm precipitation average by 1.02 inches, while 2010 marked the 14th consecutive year when the average annual temperature topped the longterm average.

That extra precipitation provided some tangible benefits, reducing the extent of areas experiencing drought to roughly 8 percent of the country by July. At the same time the moisture contributed to fewer wildfires. By fall, however, drought conditions began to expand into the South.

So far, the average annual temperature in the U.S. has been rising about 0.12 degrees F per decade since 1895, while precipitation has been rising by around 0.18 inches a decade.

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