Peter Lehner pauses a moment in Central Park. Steve Halin

For three weeks in the summer of 1985, Peter Lehner, then 27, and his new wife kayaked through the fiords of Alaska's Prince William Sound, sleeping on the beach at night, learning to recognize the sounds of whales surfacing, and growing comfortable with the sensation of being quietly watched by seals. The newlywed pair returned home to New York City, where Lehner, not long out of Columbia Law School, was due to start working in the office of the city attorney.

Lehner, now NRDC's new executive director, was just a few years into his job with the New York City attorney -- prosecuting wastewater treatment plants upstate for polluting the city's drinking water supply -- when, in March 1989, the Exxon Valdez ran aground in Prince William Sound, triggering one of the largest oil spills and worst environmental disasters in history. The New York Times ran a picture of an oil-slicked beach on Alaska's Knight Island, the very same spot where Lehner had slept on his honeymoon. Less than a year later, on January 1, 1990, New York Harbor was despoiled by the biggest oil spill in the city's history. Outrage over the devastation reached a fever pitch, and David Dinkins, then the mayor of New York City, ordered the creation of a special unit for environmental prosecution within the city attorney's office. He appointed Lehner as its head.

Lehner would go on to win dozens of lawsuits against polluters who were violating the Clean Water Act and other landmark environmental protection laws before joining NRDC in 1994 to lead its clean water program. For the next five years, Lehner spent much of his time negotiating with local governments, persuading them to modernize their storm sewers; it may sound mundane, but oily, trash-strewn runoff is the nation's single largest source of water pollution. When Newt Gingrich rose to power in Congress and tried to carve giant loopholes in the Clean Water Act, Lehner's lobbying and litigating helped hold back the attack.

In 1999, Eliot Spitzer, then the attorney general of New York State, tapped Lehner to head up his environmental law bureau, and it was there that Lehner established himself as the legal mind behind some of the biggest environmental battles of the past decade. To reduce smog in New York, he sued dirty, coal-fired power plants in the Midwest for violating a provision of the Clean Air Act known as the new source review rule. These cases became the largest air pollution enforcement campaign ever undertaken in the nation, forcing power companies to install updated pollution controls that promise to save thousands of lives that would otherwise be lost to respiratory illness.

In the absence of federal action on global warming, Lehner devised innovative legal strategies to take the matter into the hands of New York State. In 2005 he turned to the federal common law of nuisance, which has been used for 200 years to protect clean air and water. Lehner led a coalition of seven states and NRDC in suing the nation's five largest carbon dioxide polluters. The case is still winding its way through the courts, but it has already sent a powerful message to industry: "Global warming pollution is no different from any other kind of pollution," Lehner says. "It can and must be stopped."

Lehner's successful model of aggressive state activism on global warming motivated other states to follow New York's lead. In 2005, 12 states, including Massachusetts, New York, and California, as well as the city of New York, filed suit against the federal Environmental Protection Agency for failing to regulate global warming pollutants. The case went all the way to the Supreme Court, and in April the Court ruled that the Clean Air Act in fact grants government agencies the authority to regulate carbon dioxide, just as it does any other air pollutant.

"Peter has a brilliant -- and creative -- legal mind," says Mitch Bernard, NRDC's head litigator. "He was one of the most vigorous and effective environmental advocates in state government -- ever." As of the first of this year, it was NRDC's turn to lure Lehner back, and now, in his role as executive director, he is putting his fierce intellect and relentless passion to work on behalf of all of NRDC's programs and priorities.