Global warming was top-of-the-hour news last week because of a report in the New York Times that open water had been spotted at the North Pole for the first time in perhaps 50 million years. Turns out the Times overstated the development; in a correction today and a follow-up article, the newspaper reports that some scientists believe there have probably been clear spots at the pole before because about 10 percent of the Arctic Ocean is clear of ice in a typical summer. Data do show that the ice pack in the region is shrinking in area and thickness, and that on average, temperatures in the Arctic Ocean have risen 11 degrees over the past 30 years and are the warmest in four centuries. But scientists are unclear whether the shifts are part of a natural cycle or are a loud warning signal that the effects of global warming are already upon us.