"The fear is that an increased search for oil is going to impact the Arctic, but the experience we've had is that activity has already peaked," he told Reuters in an interview.

The survey of potential impacts from oil and gas exploration in the Arctic is part of a wider Arctic Monitoring and Assessment Programme, sponsored by the United States, Russia, Canada and the five Nordic nations.

Norway has lifted a ban on drilling in the little-explored Barents Sea as oilfields further south have begun to mature, and the US government wants Congress to approve drilling in Alaska's Arctic National Wildlife Refuge to boost oil supplies.

Thurston said the study will recommend that countries improve their plans for coordinating handling of a major oil spill in the Arctic seas.

"Three things happen with a big spill: there's a lot of death of animals, there's the long-term effects with oil persisting in the environment and there's the psychological effect," he said.

"Seeing a pristine area covered in oil changes policy, people's perceptions, and it's certainly bad for the oil business," he added. Scientists said last month effects still lingered in Alaska from the 1989 Exxon Valdez spill.

Experts gathered in Helsinki for a three-day working meeting have found that most environmental damage in the Arctic due to oil and gas exploration occurred in previous decades, with new technology now permitting less drilling and low pollution.

"The way people act in the Arctic has changed a lot. (Exploration) is a lot cleaner, it's a lot smaller and it's more focused. The activity level is going down even if the search for oil is ramping up," Thurston said.

He said he believed Norway's decision to lift the drilling ban in the Barents Sea, which prompted loud protests from environmental groups, was unlikely to cause damage.

"The technology is really safe and there's been a tremendous amount of risk assessment done on the Arctic projects. Personally I think they are safe operations," he said.