Dozens of big-name music stars gather at venues all around the world for Live Earth concerts to promote awareness of global warming and push for immediate change.
But as the events kick off, critics have questioned the true environmental devotion of some of the acts and the use of gas-guzzling private jets, SUVs and limousines.
One superstar in particular is facing some last-minute scrutiny.
Madonna is taking the stage at London's Live Earth in support of the environment, but her charitable foundation has invested heavily in the corporate world, including several large companies that are often criticized for the harm they do to the planet.
The Ray of Light Foundation has owned, within the last two years, shares of companies that log forests, drill for oil and mine for metals.
The holdings have included paper goods giant Kimberly Clark, forest products company Weyerhaeuser, aluminum giant Alcoa and oil company BP, according to the foundation's annual report filed with the Internal Revenue Service.
But the portfolio also includes numerous other stocks, including Allstate Insurance, food-service company Aramark, chip-maker Intel, eBay, CVS and Texas Instruments.
There are plenty of other stars performing. But their investment choices are private. Because Madonna has a tax-exempt foundation, her foundation's investment choices are part of the public record.
Nothing in Madonna's foundation's portfolio is out of line with the holdings of a typical foundation, pension fund or any other investor.
Rona Fried, editor and publisher of progressive investor, said the portfolio looks like a typical large cap portfolio.
"She's got some good companies and some not-so-good companies," Fried said.
Fried said that BP is "one of the better oil companies" and noted that Madonna's foundation also owns Nike, which she considers one of the top 20 sustainable stocks out there.
The portfolio breakdown is dated Dec. 31, 2005. It is the latest filing with the IRS. It is possible that Madonna has changed her investing strategy since then.
"Being that this is two-year-old information, she might not have any of this anymore," said Cliff Feigenbaum, publisher and managing editor of the GreenMoney Journal. "We're getting old information."
ABC News was unable to reach Madonna's California foundation or its lawyer, but filings show that Madonna controls 100 percent of the foundation.
Feigenbaum wouldn't comment on how good or bad the companies are but said he wouldn't invest in them.
So, should a celebrity who is part of a concert for climate change be held to a higher standard? Should she sacrifice returns at her foundation to be as green as possible?
A spokesman for Live Earth said he had not seen the foundation's investments and could not comment. When ABC News offered to e-mail a copy of the holdings to him, he declined, saying he was on a train and too busy with the event to review it.
Just because people invest in a company doesn't mean they agree with the corporate philosophy, Feigenbaum said.
"In socially and environmentally responsible investing, one of the most important and effective strategies is shareholder activism," Feigenbaum said. "You have to own stock in a company to change it in a positive direction by filing shareholder resolutions."
Not speaking specifically about Madonna, Feigenbaum said that investors might purchase stock in a company to push such issues as executive compensation, climate change and disclosure and transparency on the environmental impact of the company's products.
Feigenbaum also noted that often the investment arm of a foundation is out of line with the program side of an organization.