Environmental advocacy group the Sierra Club endorsed President Obama Wednesday, supporting his 2012 reelection campaign.

Because President Barack Obama has stood with us on the side of health, prosperity, and progress for all American families, I am proud to announce that the Sierra Club is endorsing him for reelection, wrote Sierra Club Executive Director Michael Brune in a statement.

Several other major environmental groups have thrown their support behind the president, including the League of Conservation Voters, Clean Water Action and Environment America.

Elections are about choices -- and for those who care about building a clean energy economy and confronting the climate crisis, the choice is clear: President Obama is a clean energy champion and Mitt Romney is a climate denier, said LCV President Gene Karpinski in a statement. While President Obama has fought to put Americans in control of our energy future, Mitt Romney and his Big Oil buddies would take us back to the failed dirty energy policies of the past.

It is not surprising that these environmental groups have chosen to back Obama. In the 2008 election, Obama received endorsements from the Sierra Club and LCV in June and July respectively, which makes Wednesday's endorsements an early show of support.

In Brune's endorsement statement, he touted Obama's regulation of power plant emissions through the Environmental Protection Agency as a highlight of his environmental record.

To protect the health of our kids and communities, 800,000 of us called on the EPA to limit toxic mercury pollution from coal plants for the first time ever -- and President Obama acted, Brune wrote. New protections will slash mercury pollution from power plants by more than 90 percent and improve air quality for millions of Americans.

LCV also praised Obama for reducing tax breaks for oil companies, raising fuel efficiency standards and increasing use of solar and wind energy.

Romney's campaign dismissed the endorsements, and criticized Obama's environmental policies as impediments to economic growth.

It is no surprise that liberal environmental groups support President Obama's agenda of shutting down energy sources, driving up energy prices, and shoveling billions of taxpayer dollars to their favorite green projects, Andrea Saul, a Romney spokeswoman, told the Los Angeles Times. Governor Romney is focused on earning support across the country from Americans who are committed to protecting the environment while promoting instead of stifling economic growth.

The Obama campaign welcomed the endorsements.

We're honored to have the support of the Sierra Club, the League of Conservation Voters, and Clean Water Action and Environment America, and we look forward to working with them throughout the campaign, Jim Messina, manager of the Obama campaign, told the Times. President Obama is fighting for an economy that's built to last, and that's why he's investing in clean energy and responsibly developing our natural resources in a way that creates good jobs here in America, protects the environment and reduces our dependence on foreign oil.