Democrats in the US House of Representatives are expected to announce a compromise move on Wednesday that would give the go-ahead to a bill to tackle global warming. Success would beat expectations in a political climate increasingly hostile to cap-and-trade.

The bill, which will disappoint some environmental groups, is likely to give away more than half the carbon permits under the cap-and-trade system, and water down the original emission reduction targets envisaged by the two leading congressional sponsors, Henry Waxman of California and Ed Markey of Massachusetts.