Less than a week before the 2012 election, I endorsed President Barack Obama for one main reason: his commitment to confronting climate change with bold new initiatives. New York City had just come through Hurricane Sandy, and it was painfully clear that rising sea levels and intensifying storms could no longer be ignored in Washington.

We needed the federal government to take action, but almost nothing had been done since cap-and-trade legislation failed to pass the Democratic-led Senate in 2010. During the 2012 campaign, the president promised that would change ― and tomorrow, he is expected to make good on that promise, through the Environmental Protection Agency’s new proposal to limit greenhouse-gas emissions nationwide.

We have waited a long time for the EPA to take action. In 2003, a number of states and cities (including New York City) filed a lawsuit arguing that under the Clean Air Act, the EPA had both the authority and the responsibility to regulate carbon dioxide emissions, because they present a clear danger to society. In 2007, the U.S. Supreme Court sided with us. Since then, the challenge of climate change has only grown more urgent, and the cost of inaction more dire.

Climate change is already disrupting local economies, destroying critical infrastructure and uprooting people’s lives. At the same time, some health problems resulting from fossil fuel combustion, such as asthma attacks, have doubled in the last three decades. Pollution emitted from coal-fired power plants alone kills 13,000 Americans every year and sicken tens of thousands more.

The EPA’s actions will significantly improve public health, while also enhancing U.S. leadership on climate change. Other countries have been waiting for the U.S. to lead by example, and tomorrow’s action will make it harder for them to remain on the sidelines. As the United Nations special envoy for cities and climate change, I see firsthand how closely the world is watching what America does. This step will help give President Obama the credibility he needs to persuade other countries to take action.

The EPA’s new rules will give all 50 states the flexibility to determine for themselves the most effective ways to reduce their carbon emissions. For instance, states are likely to adopt more energy efficiency measures, as we did in New York City. Although energy efficiency requires upfront costs, those investments get repaid and eventually produce savings. We found that most businesses and building owners understood this, and many of the city’s largest businesses and employers (including hospitals and universities) voluntarily agreed to match the city’s carbon-reduction efforts.

We also found that carbon-reduction strategies strengthened economic growth. The cleaner a community’s air, the more it can attract residents and businesses. In just six years, we reduced New York City’s carbon footprint by 19 percent ― even more than what the EPA has proposed ― while at the same time far outpacing the nation in economic growth. In fact, no large city in the country had stronger economic growth during this period than New York, and no city in the country took more ambitious steps to reduce its carbon footprint. We didn’t grow in spite of carbon reduction; we grew, in part, because of it.

As a result, New York City’s air is cleaner than it has been in 50 years, and life expectancy has grown much faster than in the rest of the nation. People are living longer and healthier lives, in communities with businesses that are growing and creating jobs: That was our experience with carbon reduction, and more and more cities and towns are experiencing it, too.

The new rules expected tomorrow are open for public comment and challenges by Congress ― and they won’t be finalized for another year. Then, states will have a year to create implementation plans. It’s up to the administration to keep this process moving as quickly as possible, and to make the rules as strong as possible.

For the world to confront climate change, Washington needs to help lead the way. Now, finally, it is.

By Michael R. Bloomberg

Michael R. Bloomberg, the former mayor of New York City, is the founder and majority owner of Bloomberg LP, the parent company of Bloomberg News. ― Ed.