Americans are beginning to take climate change very seriously. One measure of that is Wall Street’s reluctance to invest in environmentally questionable activities. The TXU Corp. takeover is a case in point.

Environmentalists had been beating on TXU over its plans to build 11 new coal-fired electricity plants — which would pump out planet-heating greenhouse gases. Their campaign helped send TXU’s stock into a swoon, from $67 a share to $53. And that cheaper price for the company caught the eye of Kohlberg Kravis and Texas Pacific, two major private equity firms.

Environmental Defense and other green groups had been publicly hitting hard on TXU. Now, private equity companies are barely regulated and usually try to stay out of the limelight. They know that any battle with sophisticated environmentalists could bring unwanted attention to their various business doings.

So executives representing the purchasers contacted environmental activists and offered assurances that if the deal went through, the new owners would build only five or six new coal-fired electricity plants, not the 11 in the original plan. They wanted the environmentalists, led by Environmental Defense, to support the $45-billion sale, which, incidentally, would be the biggest buyout in history. In the course of the discussions, Environmental Defense is said to have strengthened the environmental requirements.

Enter also the Wall Street environmentalists. Goldman Sachs, the lead adviser for the equity firms, is famous for its environmental conscience. Treasury Secretary Henry Paulson, a Goldman alumnus, was also chairman of the Nature Conservancy.

And a founder of Texas Pacific, David Bonderman, belongs to the World Wildlife Fund board, of which William K. Reilly, a Texas Pacific executive, was chairman.

“We didn’t want to be on the wrong side of history,” a member of the bidding group told The New York Times. Clearly, there is environmental heart in the decision to cut back on coal-plant building — in addition to the business considerations. Not building all those plants would free up money for other things, among them, helping the buyers finance the enormously expensive purchase.

The struggle over coal plants and their environmental impact will continue. Even a planned TXU coal plant that has survived the agreement is meeting stiff opposition from its neighbors in Waco, and a panel of Texas administrative law judges has advised against it. Although the law doesn’t regulate emissions of greenhouse gases, it does concern itself with particulate pollution that electricity plants release, which we breathe in.

Environmentalists much prefer another TXU proposal, to build a power line to a planned wind-farm kingdom in West Texas. That’s more like it.