Temperatures in the Arctic are now the highest they've been for 2,000 years, according to scientists. Researchers in the United States say that it is one of the 21. signs yet that human activity is warming the planet. Scientists have produced 22. showing dramatically that the current temperature rise there is highly 23. . For most of the last two thousand years, the Arctic slowly cooled, a consequence of variations in the Earth's orbit. But over the last century, the cooling abruptly 24. , and the region is now warmer than at any time in the 2,000 year record. Writing in the journal Science, the researchers say this shows how quickly the Arctic 25. to climatic changes.