WASHINGTON 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.
* Some environmentalists hope the climate change bill can be strengthened in the Senate. They back increasing the amount of electricity utilities must generate from renewable energy sources, raising emission reduction goals and auctioning more pollution permits instead of giving them away to companies.
* "Some senators plan to create more jobs in the wind and solar industries by improving the renewable electricity standard," said Dan Weiss, energy expert at the Center for American Progress. "The recent government study that documents the current impact of global warming on the United States may spur some senators to seek steeper reductions in greenhouse gas pollution by 2020."
* The House bill calls for auctioning only 15 percent of the pollution permits and giving companies the other 85 percent free. Many environmental groups want to auction more, and if the Senate modifies the current permit arrangement, some House lawmakers may not back a final bill.
* There is a chance the Senate legislation could be weaker than the House version in order to avoid a filibuster. "That means a Senate-passed bill will only be as good as the views of the 60th senator. So the deal-making in the House may be only a preview of things to come in the Senate," said Frank O'Donnell, head of Clean Air Watch.
* Stronger lobbying by the White House may be needed to win Senate approval.
* "President Obama should argue that this bill would improve national security by reducing oil use and limiting the international instability that would occur with more drought, famine, and floods. National security concerns could convince some senators to support this program if economic and environmental concerns do not," Weiss said.
* White House press secretary Robert Gibbs said on Friday the president "believes it's possible to get (climate change) legislation through the Senate and to his desk."
(Reporting by Tom Doggett)