NEW YORK (CNNMoney.com) -- An executive at American International Group, one of the largest insurance firms in the world, said he believes a tax on carbon emissions, long opposed by the Bush administration and legislators on both sides of the political isle, is coming to the U.S.

"Companies that are irresponsible carbon emitters pay a price, and in the U.S. I believe they will pay for it," Win Neuger, chief investment officer at AIG, told an audience at a Cleantech venture capital conference in New York City. "I, as an investor, have to look at potential legislation that will put that risk on me."

Several countries have begun taxing business and motorists on carbon dioxide emissions - one of the principal greenhouse gasses - in an effort to comply with the Kyoto treaty on global warming.

So far U.S. lawmakers have resisted both a carbon tax and signing the Kyoto treaty, arguing a carbon tax will crimp the country's economic growth and that the Kyoto treaty will do relatively little to reduce emissions while costing a great deal.

Other experts close to high carbon emitting industries - like utilities - have also said they believe a carbon tax is coming and have urged the government to pass a carbon tax so industry can proceed with long term capital investments with more certainty.

At the investment conference, Neuger laid out several reasons to invest in clean, socially responsible companies, including reduced risk from lawsuits and negative brand image, and the ability to attract higher caliber employees.

But most importantly, he said clean companies are profitable, noting that the Dow Jones sustainability index has outperformed the S&P 500, often substantially, for the last three years.

"There clearly is not a socially responsible investment penalty," he said. "In fact, there has been a clear upside."

AIG (down $0.06 to $65.52, Charts), through its Global Investment Group, has $535 billion in asserts under management. Rival Berkshire Hathaway (Charts)'s stock was down in morning trade on the New York Stock Exchange.

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