The Heat Is Online

Minnesota Soil Temperature Rise Reflects Warming

Soil temps convince scientist warming is real
ENVIRONMENT: A U of M professor has been recording soil temperatures in St. Paul for 42 years.


ST. PAUL - Donald Baker isn't the type to jump on the latest bandwagon. When global cooling was all the hubbub in the 1970s, he kept his distance. When global warming got traction in the 1990s, he resisted.

But Baker, an 81-year-old retired University of Minnesota professor, has thrown a nod, ever so reluctantly, to the warming crowd. And he has the numbers to back it up.

Since 1962, Baker and his colleagues have been recording soil temperatures as deep as 42 feet below an open field on the north edge of the university's St. Paul campus. The measurements show sub-surface soil temperatures have increased more than 3 degrees Fahrenheit, a much faster rise than would be expected in a more stable climate.

"There has been an increase that, I think, one cannot deny," said Baker, a trim man with white hair and mustache. "And there appears to be a certain part of this that is man and his putting certain pollutants into the atmosphere."

Baker's research only deals with a small geographical area, but it supports what a growing body of climate scientists worldwide have been saying for years: that the Earth is warming and that human activities are playing a role.

The Earth's average surface temperature has increased 1.1 degree Fahrenheit in the past century, with a quicker warm-up projected this century because of a buildup of heat-trapping greenhouse gases such as carbon dioxide, methane and nitrous oxide. That, those scientists predict, will lead to dramatic changes in the Earth's climate.

When Baker and his university students first started their measurements, there was no global warming debate. Specializing in agricultural research, Baker said he was interested in measuring the temperatures below ground after noting efforts at the Argonne National Laboratory near Chicago. Measurements there, he said, went down almost 30 feet, but showed some influence from surface temperatures.

Baker sought a depth that wouldn't show that variability. "We thought, 'Why don't we go as deep as we can, and see what goes on down there?' " Baker said.

They tried, but rock hindered their efforts, and they only got as deep as 12.8 meters, or 42 feet. Once he and his crew installed their equipment, they began recording soil temperatures, wind speeds, evaporation, solar radiation, and other meteorological data, establishing a model of climate variability that other scientists have praised for its duration and continuity.

"At the time he installed this observatory, a lot of people probably were puzzled what his long-term goals were," said Henry Pollack, a geophysics professor at the University of Michigan who calls Baker's research pioneering. "It turns out to be one of the longest continuing records of soil temperature, I think, in North America."

Baker's four-decade temperature record, he cautioned, represents but one piece of a global puzzle. "One has to be careful," Pollack said. "It demonstrates St. Paul warming. With enough places around the globe, we can piece together a global picture."

Mark Seeley, university climatologist and meteorologist, also called Baker's work significant.

"He was one of the first in the country to start up a climate observatory and monitor all the relevant climate factors, one of which is ground temperature," said Seeley, who marvels that Baker still conducts research.

"He is one of a few faculty members who has been published in six different decades," Seeley said. The university recently gave Baker its outstanding achievement award. He retired in 1994, but continues as a professor emeritus in the department of soil, water and climate.

In addition to starting the university's climate program and his work with soil temperatures, Baker's measurement and analysis of wind conditions has helped Minnesota become one of the nation's leaders in wind-energy production.

That's a long way from where Baker started, growing up in St. Paul during the hot, dry 1930s, and using street cars to get places.

Like many of his peers, Baker's life took a different direction in World War II, when he left the University of Minnesota and volunteered for military service. The military sent him to meteorology school, providing him with an education he grew to appreciate. He served as a weather forecaster until 1946 and again during the Korean War.

During that period, he also got his undergraduate and graduate degrees from the university. In 1958, he began teaching there, developing courses in meteorology and climatology, primarily to benefit agriculture.

His office has always been on the St. Paul campus, with the climate data being collected on a small site in the middle of a nearby field. There, a collection of older wind, solar and temperature gauges are surrounded by a tall chain-link fence.

The below-ground readings, recorded at several depths, show the same gradual upward temperature direction. Deeper readings show progressively less seasonal fluctuation, with the 42-foot readings showing little annual or seasonal wiggle. An "urban heat-island effect" associated with populated areas only accounts for a third of the below-ground temperature increase, Baker said.

What all of that appears to add up to, he said, is that the Earth is simply warming up.

"In the past, we've assumed that what was coming in was going out within a year," Baker said, referring to the sun's energy. "We had gained as much as we had lost or we had lost as much as we had gained. Now, it appears that more is being retained."

Baker said he has been extremely cautious about interpreting the soil temperature data.

"I was greatly influenced by the '70s," he said, referring to a spate of speculation and media reports in the mid-1970s that, following a period of slight atmospheric cooling, predicted the onset of another ice age.

But more than four decades of temperature readings showing a steady increase in ground heat storage have convinced him this trend is for real.

"It takes quite a bit to sway me," Baker said. "I take pride in that."