Environmentalists from Bill McKibben and Paul Hawken, to Fred Krupp and Frances Beinecke offer President Obama their advice on the priorities he should set for the first 100 days of his administration.

In evaluating an economic recovery package, the new U.S. administration and Congress must weigh any proposed spending on highways or mass transit or wind-power transmission routes on the basis of clear criteria that would assess just how green the projects will be.

In an interview with Yale Environment 360, Amory Lovins, co-founder and chairman of Rocky Mountain Institute, says that world's biggest untapped energy source is efficiency. And retooling for energy efficiency will require "barrier-busting" at many levels. And government, Lovins says, "should steer, not row."

As he assumes the presidency, Barack Obama must make climate-change legislation and investment in green energy top priorities. And he must be ready to take bold — and politically unpopular — action to address global warming.

The next U.S. president should not wait for Congress to act on climate-change legislation. Instead, he should make use of the Clean Air Act to begin controlling greenhouse gas emissions and to implement a national cap-and-trade program.