The U.S. Environmental Protection Agency (EPA) says failure to act on global warming will kill hundreds of thousands of Americans by the end of the century and cost the country trillions of dollars.
The EPA issued a new report Monday, spelling out the consequences of what could happen if the world's temperature climbed a staggering 5 degrees Celsius by 2100 because of inaction.
EPA chief Gina McCarthy said "We can save tens of thousands of American lives and hundreds of billions of dollars annually in the United States by the end of this century. But the sooner we act, the better off America and future generations of Americans will be."
The report was put together by the EPA and several leading independent laboratories.
It says tens of thousands of American deaths from extreme temperatures and poor air quality in cities could be avoided each year by taking action.
Trillions of dollars in damage caused by storm surges and a rise in sea level could be saved.
If nothing is done, the EPA says, California could see more drought, the west could suffer through more wildfires, and the east coast could be battered by heavy rains and storm surges.
Most scientists say human activity, including burning fossil fuels like coal and oil, create emissions that cause global warming. They say the cost of doing nothing would be catastrophic for life on Earth.
Others say climate change is caused by natural weather patterns that have persisted since the Earth was formed and that drastic action would bring economic disaster.
Delegates from around the world will meet in Paris in December to try to hammer out a legally-binding agreement on tackling global warming.
The issue drew the attention of Pope Francis who said in a letter to the world's Catholics last week that "Humanity is called to recognize the need for change of lifestyle, production, and consumption, in order to combat this warming or at least the human causes which produce or aggravate it."