US President George W Bush plans on Wednesday to call for halting the growth of greenhouse gas emissions by 2025. The three candidates vying to succeed him have made more ambitious proposals. Here is what they are saying about environmental and energy issues: * CLIMATE CHANGE New York Sen. Hillary Clinton, Democrat - Cut US greenhouse gas emissions to 80 percent below 1990 levels by 2050 through cap-and-trade system; require all publicly traded US companies to file report on climate change risks with the Securities and Exchange Commission. Illinois Sen. Barack Obama, Democrat - Cut carbon dioxide (CO2) emissions to 80 percent below 1990 levels by 2050; reduce emissions to 1990 levels by 2020; require fuel suppliers to cut carbon content by 10 percent by 2020. Arizona Sen. John McCain, Republican - Favors cap-and-trade CO2 approach; sponsored legislation in 2007 to cut emissions by 30 percent by 2050. * VEHICLE FUEL ECONOMY Clinton - Boost corporate average fuel economy standards, or CAFE, to 55 miles per gallon by 2030, offer $20 billion in "green vehicle bonds" to help US automakers meet standards, invest in plug-in hybrid technology. Obama - Double fuel economy standards in 18 years, give automakers tax credits to retool plants and invest in advanced lightweight materials and new engines. McCain - Has not specified CAFE targets. Voted against energy amendments in 2003 that would have boosted CAFE to 40 mpg by 2015. * BIOFUELS Clinton - Make 60 billion gallons of biofuels available for trucks and cars by 2030. Obama - Boost renewable fuel standard to at least 60 billion gallons of advanced biofuels like cellulosic ethanol by 2030; build out ethanol distribution infrastructure; mandate that all new vehicles be "flexfuel" by the end of 2012; produce 2 billion gallons of "cellulosic" ethanol from non-corn sources like switchgrass by 2013. McCain - Favors ethanol incentives after opposing them in the past. Generally opposes subsidies and tariffs that distort marketplace. * OIL USE Clinton - Cut foreign oil imports by two-thirds from 2030 projected levels, more than 10 million barrels per day. Obama - Reduce overall oil consumption by at least 35 percent, or 10 million barrels per day, by 2030 to offset imports from OPEC nations. McCain - No specified targets. Has said he will unveil "a national energy strategy that will amount to a declaration of independence from the fear bred by our reliance on oil sheiks." * ELECTRICITY Clinton - Wants to require US utilities to get 25 percent of their electricity from renewable sources like wind and solar by 2025. Obama - Backs 25 percent renewable requirement by 2025. McCain - Opposed 2005 proposal for 10 percent requirement, emphasizes market choice. SOURCE: campaign Web sites (Reporting by Chris Baltimore; editing by David Wiessler) REUTERS NEWS SERVICE