Four decades of resource extraction in Alaska’s North Slope has been a mixed bag for the region’s environment and people, according to a study released yesterday by an 18-member panel of the National Research Council, the research arm of the U.S. National Academies. The study, which is the first-ever assessment of the cumulative impact of oil exploration and production in the slope, found that oil spills have not been a major problem but noted the negative impact on the region of more than 1,000 miles of roads and pipelines, as well as other infrastructure elements. It also raised concerns about who will take responsibility for cleaning up the area when the oil and gas companies leave, and it questioned whether the industry has contributed to increasing alcohol abuse, diabetes, obesity, and other problems among area residents. Sen. Ted Stevens (R-Alaska), who commissioned the study in 1999, criticized its findings, saying it underestimated the benefits the oil industry has brought to the region.