The federal Minerals Management Service gave the green light to Shell Oil's plan to drill exploratory wells in the waters of the Chukchi Sea off Alaska's northwest coast next summer. "We are very concerned because drilling for oil runs the risk of devastating spills in a sensitive marine ecosystem already stressed by dramatic climate change," said Marilyn Heiman, director of the Pew Environment Group's U.S. Arctic program. Shell purchased a swath of oil leases in the Chukchi Sea in 2008 when the previous administration opened up 30 million acres for drilling. Beginning in July 2010, Shell plans to drill three exploratory wells - the first time in 19 years that drilling will be allowed in the Chukchi Sea northwest of Barrow.