Last November, House officials spent about $90,000 to buy carbon offsets in an attempt to make the House carbon-neutral by the end of the 110th Congress.

But a new report from the Government Accountability Office finds that such carbon offsets are unregulated and hard to validate.

In an interview, the report’s author said it’s premature to use offsets to claim carbon neutrality.

Such claims can only be made “if the carbon offsets can be validated. Right now, that’s questionable,” said John Stephenson, director of the GAO’s Natural Resources and Environment division. “I mean, there’s no standard system for doing those validations.”

It’s welcome news to Republicans, who have widely criticized Chief Administrative Officer Dan Beard for buying the offsets and argue that the purchase was a waste of taxpayer money.

Beard has consistently defended the purchase, pointing to the reputation of the Chicago Climate Exchange and the approval of oversight committees.

On Friday, House Administration ranking member Vernon Ehlers (R-Mich.) — a vocal opponent of Beard’s offset purchase — called again for a stop to any future offset purchases.

“While increased oversight of the U.S. offset market clearly merits consideration, the House’s further participation in this market does not,” Ehlers said in a statement. “The GAO report demonstrates that the rapidly growing offset market currently lacks necessary quality assurance mechanisms and consumer protection.”

Buying offsets is touted as a way for companies, agencies or even individuals to mitigate the environmental damage of their carbon emissions without physically reducing them.

For example, a company may emit 50,000 tons of carbon a year; to offset that, it could pay for projects that trap methane or reduce carbon in the atmosphere. Or it could pay for another company to keep its emissions below normal.

The House bought its offsets from the Chicago Climate Exchange, which Stephenson says is the most transparent and structured exchange in the nation (though he stressed that he had not studied the merits of the offsets themselves).

Those offsets addressed the emissions that couldn’t be reduced through other measures, such as using renewable energy and buying efficient light bulbs.

Beard has not yet claimed that the House is carbon-neutral, and it’s unclear if he ever will. Spokesman Jeff Ventura said the CAO office is “evaluating our status with regard to carbon neutrality at this time.”

Speaker Nancy Pelosi (D-Calif.) directed Beard to make the House carbon-neutral by the end of the 110th Congress as part of her Green the Capitol Initiative. The plan has a three-pronged approach: purchase renewable electricity, use natural gas for heating and cooling, and buy carbon offsets for any remaining emissions.

Beard has followed through with it all. But he’s had obstacles along the way, which are outlined in the GAO report.

Officials first ran into the problem of finding out how much carbon the House emitted. No new data was available, so they relied on data from 2006.

Then Beard bought too many offsets, spending about $24,000 more than was necessary. This resulted from an administrative error that confused a short ton, equal to 2,000 pounds, and a metric ton, equal to about 2,200 pounds. Beard purchased 30,000 metric tons, but the House only needed 24,000 short tons.

Ventura said the difference will be pushed forward to next year.

But Beard took another hit in February, when an investigation by the Washington Post found that some of the credits purchased by the House went to fund projects that had already ended or weren’t effective.

Whether and how offsets will be purchased next year is uncertain; Ventura said the CAO’s office intends to read the GAO report.

“Certainly we’re going to consider everything in the report,” he said, “but it’s just too soon. We haven’t had time to analyze it.”

Stephenson said offset markets will have to be part of any nationwide effort to reduce carbon emissions and applauded those who got into the market early. But he warned that it was a risky venture.

“I think getting into that market is a good idea,” he said, “but it’s a buyer-beware situation right now because of a lack of controls in the market.”