According to research published by two University of Utah scientists, the answer is at least 138 years, and possibly much longer. The study may improve understanding of global climate change.

"Perhaps there was significant warming of the Arctic even 100 years ago or so," said Tim Garrett, assistant professor of meteorology at the U.

Garrett and Lisa Verzella, former undergraduate students in the department of meteorology, researched the question of air pollution in the Arctic and found that particulates from industrial sources were observed by an Arctic explorer in 1870. The findings of Garrett, lead author, and Verzella are to be published in the March edition of the Bulletin of the American Meteorological Society under the title "An Evolving History of Arctic Aerosols."

In earlier work, Garrett attempted to estimate the effect of haze on the Arctic climate, particularly its effect on clouds. He showed that aerosol pollution blows northward from developed countries and into the Arctic. The pollution affects the clouds in a way that warms the arctic surface and is involved in melting the region's ice. It is most prevalent in the winter and spring.

When air pollution in the Arctic was measured in detail during the 1970s by Glenn Shaw of the University of Alaska, he said, "There was a huge amount of skepticism that this could possibly be true, that the Arctic, which is such a remote place, would have high levels of aerosol pollution."

The amount Shaw measured was equivalent to air pollution in a city at more temperate climes.

Studies continued through the 1990s, and Shaw found reports from Air Force pilots who had carried out reconnaissance flights in the Arctic in the 1940s and '50s. They had discovered haze at high altitudes, but the reports had gone largely unnoticed until Shaw dug them up.

Garrett wondered if pollution had been observed in the Arctic for a long time. "There's been pollution in the mid-latitudes for much longer than the 1950s," he decided. Could pollution from industrial facilities have drifted north "even as early as the 1800s?"

He decided to dig up records by famous Arctic explorers and check if pollution is mentioned in them.

Verzella, who was a student of his, took on the project as an undergraduate. "She did most of the groundwork for this, and we dug up all sorts of old records, old journal articles."

Several articles about the Arctic dating to the late 19th century referred to haze of the type now known to be pollution.

The first to draw attention to the haze apparently was Adolf Erik Nordenskiold, says the study. In an 1883 report, published in Science Magazine, he described the sky covered with a thin veil of clouds, and that sometimes the haze descended to the surface of the ice. Unlike water haze, the material was dry, "yes, so dry that our wet clothes absolutely dried in it," the study quotes Nordenskiold.

That geologist also noted that in an expedition to Greenland in 1870 he had found fine, gray dust wherever the recent snow had melted. When the dust was set, it was black or dark brown. He found the soot contained "metallic iron, which could be drawn out by the magnet, and which, under the blowpipe, gave a reaction of cobalt and nickel," Nordenskiold wrote.

He speculated that the dust may have come from space. But Garrett doesn't believe in the cosmic dust theory.

The samples had "the sort of metals in them that we would associate with industrial activity," he said. "There was nothing in the way of pollution controls back then, and people didn't know how to burn efficiently." The metals were markers of fly ash from smelting and from burning coal.

Fridtjof Nansen, who sailed with a sealing expedition in 1882, "observed dark stains on the ice sheet that he hypothesized were from dust transported by air from more southern lands," says the study.

A book by Nansen was translated into English for the study, with that work carried out by a student from Brigham Young University.

With the great quantities of coal that were burned in those days, he said, the Arctic of the 1880s may have been "much more polluted than it is now," Garrett said.

What does this tell us about global warming?

"That's one of the interesting things here," Garrett said. "When we do studies of global warming of the Arctic, which is a very hot topic now because the Arctic has changed so quickly, we think of the warming by man-made activities as a very recent phenomenon."

The sharp rise of carbon dioxide pollution levels is a recent change. But "there is a considerable amount of research that suggests that particulate matter from industrial pollution may also contribute to warming of the arctic."

When snow is darkened and clouds are affected, the warmth can increase.

"If pollution was possibly higher back in the 1800s than it is today, I don't want to say that warming of the Arctic by human activities was greater back then, but I think we should strongly consider that it was not zero."

In order to estimate effects of current activities on the Arctic's warming, "we need to have a baseline," he said. "And if this baseline is set at a few decades ago, rather than a few centuries ago, then perhaps we're not setting the baseline in the right place."

E-mail: bau@desnews.com