WASHINGTON - Global warming poses more of a threat to U.S. farm incomes than does the climate change bill passed by the U.S. House, which will have a negligible impact on American agriculture's bottom line, an environmental group said on Wednesday.

A more careful examination of the facts shows that climate change itself, not climate legislation, is the real threat to American agriculture, and that climate-induced crop losses will cost US taxpayers and farmers far more than could ever be caused by the (House) bill, the Environmental Working Group (EWG) said in its report.

Legislation introduced last week in the Senate aims for a 20 percent reduction in smokestack emissions by 2020 from 2005 levels. A bill that narrowly passed the House in June calls for a 17 percent cut by 2020 in pollution from utilities, manufacturers and oil refineries -- industries blamed for global warming.

The American Farm Bureau Federation has warned that the House and Senate bills will drive up sharply the cost of farm fuel, fertilizer and pesticides.

But the EWG report said cost increases -- such as higher expenses to produce crops -- resulting from the climate change bill passed are so small they would be lost in the background noise of changes to farm income caused by routine fluctuations in yield, crop prices and input costs.

Furthermore, EWG said farmers stand to lose more from weather patterns, such as flooding, drought or higher temperatures, caused by global warming.

Agriculture Secretary Tom Vilsack has said the House climate bill would increase farm expenses by $700 million, or 0.3 percent, from 2012-18. That would be offset by revenue from a carbon offset market, estimated by USDA at $1 billion a year in the near term and $15 billion in 2040.

The American Farm Bureau Federation said the House and Senate bills put us at a competitive disadvantage in international markets with other countries that do not have similar carbon emission restrictions, AFBF President Bob Stallman said last week. For the future prosperity of the U.S. economy and American agriculture, climate change legislation must be defeated by Congress.

(Editing by David Gregorio)