Pack in. Pack out.

The Presidential Inauguration Committee is hoping that the estimated 2 million people who come to see Barack Obama sworn in as the 44th president of the United States on Tuesday will do like good hikers everywhere do: leave Washington, D.C., as clean as they found it.

Thousands of people have volunteered to lend a hand in what is being touted as the "greenest inauguration in history," and for many of them that will mean picking up trash, recyclables and even horse manure along the Mall in Washington after Obama takes the oath of office.

"Just as we are committed to making this the most open and accessible inauguration in history, we are also committed to making it the most environmentally sensitive," Inauguration Committee spokeswoman Linda Douglass told FOXNews.com.

"This will be the greenest inauguration in history, because we have tried to be mindful of the potential effects on the environment that a large crowd could have. We are trying to do everything we possibly can to return Washington, D.C., to the same state in which we found it and to reduce our own footprint as much as we can."

But critics say the committee's attempt to be environmentally friendly is nothing more than political posturing and basic good behavior.

Furthermore, they say, if Hollywood stars and bigwigs really cared about the environment, they'd choose not to come to Washington at all. Rather than generate tons of emissions in their private jets and gas-guzzling SUVs, they'd have a better chance of saving the Earth if they just stayed home.

The Institute for Liberty, a conservative think tank, estimated recently that the millions of people coming to the inauguration will generate a half-billion pounds of carbon dioxide — 260 million pounds from the 600 private jets that will come to Washington, and another 260 million pounds from personal vehicles.

It says the pollution amounts to more than 575 million pounds of CO2, which would take the average U.S. household 57,598 years to produce.

The institute did not say how it derived its figures, which are debatable. But the bottom line is undeniable: the more people who fly or drive to Washington for the inauguration, the more fuel that is consumed and the more emissions that are dispersed.

"You can't on the one hand lecture about emitting CO2 and believe it's a problem, and on the other hand create such vast amounts of CO2 almost needlessly," said IFL president Andrew Langer. He said the anticipated celebrity odyssey to the nation's capital exposes the hypocrisy of Hollywood's environmentalist crowd and negates the "green" message of the inauguration.

Christopher C. Horner, senior fellow at the Competitive Enterprise Institute and author of "Red Hot Lies: How Global Warming Alarmists Use Threats, Fraud and Deception to Keep You Misinformed," agrees.

"Green means not doing it in the first place,” he said. “It doesn't mean buying a [carbon offset] certificate to wave around and paper one's conscience with."

Horner said environmentalists who choose to attend inauguration activities and applaud the event's "greenness" are "engaging in generally phony activities to add some gauze to the obvious hypocrisy."

He added that the inauguration activities won't have a huge environmental impact anyway, and the inauguration committee's teams of volunteers who will be cleaning up trash are just picking up after themselves.

"They don't deserve a merit badge for it," he said.

But Ryan Smith, EPA liaison to the Presidential Inaugural Committee, said attention to recycling and trash removal does make a difference.

"I think we're doing a lot of good things. I'm really proud of some of the creative and innovative answers that the PIC came up with when confronted with budgetary concerns and research concerns and security concerns," Smith said.

"They really did a lot of things to weigh the cost and the benefits of doing some environmental good, and ultimately this is a public awareness issue. They're taking a lot of steps to do things very publicly that show that they are taking steps to mitigate some of the environmental concerns."

The committee plans to have 100 of its 18,000 volunteers sweeping the parade area to collect trash and recyclables. Metallic heat sheets that are being made available for parade participants who suffer the effects of the cold weather will be donated afterward to the homeless. And volunteers will follow parade horses -- picking up what they leave behind so it can be sold to a local farm.

The National Parks Service and the Trust for the National Mall are also providing recycling cans up and down the mall -- along with about 5,000 portable toilets -- for the millions who attend.