New York Times: The news that atmospheric concentrations of carbon dioxide, the most important global warming gas, have hit 400 parts per million for the first time in millions of years increases the pressure on President Obama to deliver on his pledges to limit this country's greenhouse gas emissions.
America cannot solve a global problem by itself. But as Mr. Obama rightly observed in his inaugural address, the United States, as both major polluter and world leader, has a deep obligation to help shield the...