What happens in the U.S. Senate on climate change

By Tom Doggett - Analysis

WASHINGTON (Reuters) - Historic climate change legislation, headed for a close vote in the U.S. House of Representatives, is expected to face another tough battle and likely changes in the Senate.

The House bill would slash U.S. carbon emissions produced by utilities, manufacturers and other companies by 17 percent from 2005 levels by 2020 and 83 percent by 2050.

The emissions would be cut gradually through a market in which companies buy and sell carbon pollution permits.

* Unlike in the House where a simple majority is needed to pass legislation, the Senate needs 60 votes from its 100 members to end debate about controversial measures.

* Democrats and their supporters now control 59 Senate seats. If Democratic candidate Al Franken is declared the winner in Minnesota's long-disputed senate election, Democrats would theoretically have 60 votes needed to end a potential filibuster, in which opponents to a climate change bill may try to prevent a vote on the measure by prolonging debate indefinitely.

* But some Democratic senators from states that produce coal, a major emitter of carbon dioxide -- would have a hard time supporting the climate change bill.

* Senate Democratic Leader Harry Reid has ordered Senate committees to finish work on climate change legislation by mid September, so a final measure can hopefully clear Congress this year. "This fall we're going to have a bill here in the Senate that we're going to be able to vote on," Reid said.

* Sen. Barbara Boxer of California, head of the Senate Environment and Public Works Committee, expects to unveil a climate change bill in July and have her committee pass it before lawmakers leave for their summer recess in August.