Obama has unveiled today new plans for the US to cut their carbon emissions by 30%.
The Environmental Protection Agency has set out new rules which will allow states to set their own flexible targets.
It's the first time that the country's 1,000 power plants face limits on carbon pollution. These plants account for almost 40% of US carbon emissions.
Different states have a number of options to meet the required targets: improving power plant heat rates; using more natural gas plants to replace coal plants, or ramping up zero-carbon energy, such as solar or nuclear.
Reuters news agency reports that states which rely heavily on coal-fired power plants are thought to have the toughest tasks ahead.
The EPA forecasts that regulating plants which use fossil fuels could yield over $90 billion dollars in climate and health benefits.
It also estimates that reducing exposure to particle pollution could prevent up to 150,000 asthma attacks in children and as many as 3,300 heart attacks in less than two decades.
