It's been cold lately. Frigid nights and mornings have caught the attention of Seattlelites, but nature hasn't taken much notice.

At Tuesday's weekly weather discussion in the department of atmospheric sciences, professor Cliff Mass pointed out that the last week of March in Seattle was the coldest on record.

According to the National Weather Service, the average high temperature over the last seven days of March was 46 F, well below the normal high of 55 F. The combination of the jet stream skirting south of the region and La Nina conditions in the tropical Pacific Ocean were largely to blame for such anomalous temperatures.

Despite the unseasonably cool weather, harbingers of spring aren't hard to find. The Mariners are back at Safeco Field, Canadian geese have taken to Rainier Vista and the cherry blossoms are in full bloom in the Quad.

Precise bloom data for the cherry trees isn't taken, but those responsible for the care and maintenance of the trees have a keen understanding of their tendencies.

"[The trees] generally start to bloom about a week or two before the end of March," said Clarence Geyen, supervisor of grounds maintenance at the UW. "By the first of April they're as bright and pretty as they get."

The flowering of cherry blossoms at the National Mall in Washington, D.C., hasn't been as easy to predict. In mid-March, The Associated Press reported that the bloom was primed to peak five to six days earlier than April 5, the long-term mean.

As regularly as spring seems to arrive in Seattle, this isn't the case everywhere. From the eastern United States to Europe and Asia, citizens and scientists have documented changes in the timing of the seasons.

Astronomically speaking, spring started March 21 - the vernal equinox. From then on, the earth's axis and northern hemisphere, are tilted increasingly toward the sun, lengthening hours of sunlight and raising average temperatures in the north.

Scientists are starting to collect more data and interpret it judiciously, spurring the term "season creep."

The study of the relation of climate to the timing of natural events like the appearance of migratory birds and the blooming of trees is known as phenology. A groundswell has arisen in the scientific community to expand and centralize the collection of phenological data.

The National Phenology Network (NPN) at the U.S. Geological Survey, which is less than a year old, exists to collect, coordinate and monitor phenological data. Mark Losleben, NPN's assistant director, said that while phenological data underlies much research, it has never been an explicit focus in the scientific community.

"We need to change that to be more effective," Losleben said. "If we're wise in what we select, we can get an idea of the drivers of phenological change."

Using phenological data to estimate climate change impacts can be difficult. A substantial risk for misinterpretation of data exists, UW biology professor Joshua Tewksbury said in an e-mail.

"If you compare the phenology changes in two areas, and one area shows a greater shift in phenology than another, does that mean that climate change is having a greater impact on that area, or does it mean that the organisms in that area have a greater capacity to respond to climate change?" Tewksbury said.

In spite of the necessary limitations and potential pitfalls, both agreed that careful collection of phenological data is a positive step. The complexities of climate change require innovative approaches to outstanding questions.

[Reach columnist Brian Smoliak at news@thedaily.washington.edu.]

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