The White House denies the reality of climate change. It pursues a U.S. withdrawal from the Paris accord. It has removed climate change from its mission across federal agencies. Some state governments, such as Florida's, are equally defiant of the scientific consensus and look to the White House for cover. But many localities across the country are addressing the climate crisis, investing in mitigation and adaptation policies that will save lives and protect critical economic assets.The Southeast Florida Regional Climate Change Compact is an example of the impact that regional actors can make with little state or federal support.The compact is an agreement adopted by the Broward, Miami-Dade, Monroe and Palm Beach county commissions in January 2010. Dozens of municipalities within these counties have joined the compact. The founding counties, home to nearly 6 million residents and 30 percent of Florida's population, have recognized the stakes of climate change for their region.The compact founders and their partners understand the havoc that climate change will bring to South Florida, a region whose economy is based on sand, sun and waves — a region whose tourist destinations must match the dreamy picture postcard of American mythology to survive.Planners from West Palm Beach to Key West know that three-fourths of the state's population lives in coastal counties that generate 79 percent of the state's annual economy. According to the Florida Oceans and Coastal Council, these counties represent a built environment and infrastructure whose replacement value in 2010 was $2 trillion and by 2030 is estimated to be $3 trillion.The compact's Unified Sea Level Rise Projection, updated in October 2015, projects sea level rise of 6 to 10 inches by 2030, 14 to 26 inches by 2060, and 31 to 61 inches by 2100.Long-term sea level rise will endanger coastal real estate, which is connected to tourism and local property tax revenue. Should the coastal real estate market collapse due to sea level rise, counties and cities could see their revenues evaporate just when critical infrastructure investments are most urgent.But that's just one of many conceivable nightmares for South Florida.Hotter, longer summers mean higher energy bills. They also create good growing conditions for mosquitoes and mosquito-borne illnesses like Zika. Rising sea levels mean more saltwater intrusion into the local aquifer, harming drinking water. Commercial and recreational fishing are at risk. So are coral reefs, which are economic assets as well as aesthetic ones; from 2013 to 2014, John Pennekamp Coral Reef State Park, in Key Largo, generated $65.5 million in direct economic impact.The centerpiece of the compact is the Regional Climate Action Plan. Implementation has been successful across South Florida, as cities and counties share best practices and reduce their carbon footprint.Monroe County, home to the Florida Keys, will soon conduct surveys of all county roads. With this and other data, it will be able to determine how much to adjust road elevation in preparation for rising sea levels.Monroe County is also addressing carbon emissions. It is targeting a reduction in greenhouse gas emissions of 40 percent by 2030 using a 2012 baseline. Monroe County has already achieved a 20 percent emissions reduction from a 2005 baseline.Miami Beach is transforming its stormwater system and elevating roads. The conversion of the old gravity stormwater system to a pumped system, an adaptation to sea level rise, is estimated to cost $500 million. Work on the pumped system began in 2014 with the goal of finishing in five to seven years.The work of the Southeast Florida Regional Climate Change compact is essential. Its adaptation and mitigation effort supports Florida's economy. Recently, the cities of Miami and Boca Raton formally joined the compact, strengthening its influence.The compact should be a national model for how regional actors can address the climate crisis, despite White House intransigence.John Dos Passos Coggin, a freelance writer with experience in the energy sector at the nonprofit, corporate and government level, is also the author of "Walkin' Lawton," an authorized biography of the late Florida U.S. senator and governor Lawton Chiles. He wrote this column exclusively for the Times.