Worldwide, 2010 is on track to become the warmest year on record.
Scientists at the NASA Goddard Institute for Space Studies reported recently that the average global temperature was higher over the past 12 months than during any other 12-month period in history. The National Oceanic and Atmospheric Administration has released corroborating data, adding that the past four months, including June, have each individually been the hottest on record as well.
The NASA findings were based on data from 5,000 weather stations around the world, said scientist Reto Ruedy, co-author of the study. Scientists used temperature anomalies, or departures from the baseline, rather than absolute measurements to account for differences in the instruments of individual stations.
The average global temperature, computed over a 12-month period, reached a new record in May and held steady for the month of June, he said. This was despite the recent minimum in solar activity, which should have had a cooling effect on Earth.
Apparently, Ruedy said, the solar cycle "has much less impact than the warming trend."
NOAA research meteorologist Tom Knutson doesn't find that surprising. The trend has existed since records began in the late 1800s.
The new finding comes on the tail of a NASA announcement that 2000 to 2009 was the warmest decade in history.
"This is just the tip of the iceberg," Knutson said. "The models are projecting a substantial warming into the 21st century."
The temperature rise is caused by a fundamental imbalance, Ruedy said: "At this point, the Earth's atmosphere receives more energy from the sun than it emits as heat to the universe." The Earth will continue to warm until balance is re-established, at a higher global temperature.
That's another 1.1 degrees Fahrenheit if atmospheric composition does not change, according to the NASA institute's models. By comparison, global mean temperatures have risen by about 1.5 degrees Fahrenheit since 1880.
Meteorologist David Unger at NOAA's Climate Prediction Center in Maryland said that El Niño is likely a player in this year's record-setting warmth. 2010 began with "large areas of equatorial Pacific Ocean at above normal sea surface temperatures," he said. It's easier to set global temperature records when the tropics are exceptionally warm.
The El Niño phenomenon was also responsible for California's wetter-than-average winter and spring, he said. And its death, as the Pacific began to enter a cooler-than-average pattern, generated the unusually persistent trough that has brought Sacramento all that nice weather, he added.
April this year was 4.9 degrees cooler than average in downtown Sacramento. May was 5.3 degrees cooler. June 5 was the first 90-degree day of the year.
"What it did was it cooled the air over the entire region," said Dan Keeton, a meteorologist at the National Weather Service. "Most importantly for Sacramento, it enhanced the Delta breeze."
The Delta breeze is the region's natural air conditioner, he said. The ocean breeze follows the Sacramento River into the Central Valley.
"The influence can be pretty much Valley-wide in the strongest situations," Keeton said.
According to NOAA, California was one of the few spots in the world reporting below average temperatures from April through June.
On a large scale, only isolated regions in Southeast Asia and South America could say the same.
(Lulu Liu reports for the Sacramento Bee)