Oslo, Norway - Using 500-year-old logbooks and sea charts, scientists are examining the effects of global climate changes in the Arctic.
Terje Loyning, an oceanographer with the project, said there is evidence of less ice.
"Yes, we have seen climate change, but we don't know how much has been created by humans," he said on Friday.
The Norwegian Polar Institute and the World Wide Fund for Nature compiled the Arctic Climate System Study Historical Ice Chart Archive to gauge global warming on the ice around the Arctic Sea. The Norwegian Meteorological Institute also took part.
The archive contains details of climate change in and around the Arctic from 1553 to 2002.
Loyning has been collecting sea charts covering an area from Greenland east to Novaya Zemlya, Russia, to compare the amount of ice explorers encountered hundreds of years ago.
"Much has been made in recent years of the connection between global warming and sea ice extent," said Lynn Rosentrater, a scientist with the International Arctic Programme. "But prior to the development of satellites few direct observations of sea ice were made in any systematic manner."
Rosentrater said: "We believe, along with two-thirds of scientists, that the climate change in the Arctic is caused by the burning of fossil fuel," she told The Associated Press. "It is very clear that there are natural cycles, but there is a clear human footprint."
Many scientists believe that the burning of fossil fuels is causing an increase in atmospheric carbon dioxide, triggering what is called the greenhouse effect.
A higher concentration of carbon dioxide in the atmosphere would trap more of the sun's heat, possibly causing temperatures to rise.
Other methods of tracking the effect of climate change in the Arctic have used drilling deep within the ice. Ice cores contain detailed, natural records of climate change.
Using the charts of seagoing explorers, both groups said they created a massive database that extends 500 years back.
"With the charts and logbooks we can compare the ice edge as it was. We have to be a bit careful about the assessment, but there has been a steady decrease of the ice starting long before the industrial age," Loyning told the AP.
"We have to assume that those who travelled without engine power sailed in areas where a third of the ocean was covered by ice."
The oldest records are from 1553 when English explorer Hugh Willoughby sought to find a northeastern route to China.
Willoughby and his crew perished when their ship got stuck in ice, but the voyage eventually resulted in trade between Britain and Russia. The ship's log and other documents were recovered by later explorers. - Sapa-AP