Throughout his campaign, President Barack Obama promised change. His environmental policies offer just that.

Within his first 50 days in office, Obama either reversed or ordered a review of many of the Bush administration's environmental policies -- all while working to spark action on energy projects and research.

For example, the Bush administration's offshore drilling plans are being re-evaluated, and Interior Secretary Ken Salazar has already canceled plans to drill on public lands in both Utah and Wyoming.

The Obama administration recently reviewed the Bush administration's decision to remove gray wolves from the endangered species list and is also directing federal agencies to consult with environmental and scientific experts before beginning construction in an area that could threaten an endangered species. Under Bush's policy, these reviews were optional.

One major shift in policy comes in the treatment and storage of nuclear waste. After 25 years and $13 billion in research, Obama's budget cuts off funding for the Energy Department's plans to bury nuclear waste at Yucca Mountain in Nevada. Although Yucca was not slated to open before 2020, this shift could delay the placement of the estimated 60,000 tons of highly radioactive nuclear waste that is already piling up at plants.

Obama and Bush also differ on air pollution, and Obama has already dumped a legal defense of Bush-era limits on mercury emissions from power plants. However, Obama's team has not yet created a new rule, and it may be difficult to define new standards without prompting industry challenges or encountering legal red tape.

As far as air pollution and global warming gasses are concerned, during his campaign Obama promised to slash 80 percent of emissions by 2050 and has proposed a cap-and-trade program that keeps an economy-wide lock on emissions. Under this plan, companies would be able to pay the government to emit pollutants and the money generated would be used to further research on global warming and to provide a tax cut for the middle class. By affixing a price to carbon emissions, Obama officials estimate they'll be able to generate more than $600 billion between 2012 and 2019.

The recently passed American Recovery and Reinvestment Act also had funds specified for environmental research and green-collar job creation. The stimulus bill allotted $3.4 billion for clean coal technology and fossil-fuel research.

The stimulus bill also devotes more than $11 billion to build a more efficient energy grid that incorporates clean energy technologies. Obama also ordered higher efficiency standards for household appliances like microwaves, lamps, dishwashers and air conditioners.

The recovery bill also aims to improve energy efficiency by reducing federal government consumption, increasing weatherization of low-income housing and by providing grants to states to accelerate renewable energy development and create jobs.

The Clean Energy Finance Authority was also established under the stimulus package to create and boost clean energy investments in lieu of the credit crunch, which has quashed many eco-friendly initiatives in the private sector.

Despite his ambitious goals, however, critics doubt that Obama will be able to achieve all of his energy initiatives. Although having a Democratic majority in Congress could certainly help, other national issues -- including the economic crisis -- may impede progress.