The reports followed 44 health measures connected to climate change around the world. They include heat deaths, infectious disease and hunger.
All of them are getting worse, said Marina Romanello. She is a research director of the Lancet Countdown project.
With "the world on track to 2.4°C of warming, the cost of inaction on climate and health will vastly outweigh the costs of acting now," the report says.
This year's reports are called "code red for a healthy future." One report is centered on the United States and one is centered on the entire world.
The reports found some dangerous trends:
At-risk populations like older people and the very young spent more time in extreme heat. For people over 65, the researchers found they were exposed to extreme heat at a higher rate than the average from 1986 to 2005.
More people also lived in warm places where it is easier for some diseases, like cholera or dengue, to spread. Coastlines are warm enough for the dangerous Vibrio bacteria to grow in the Baltic areas of Europe and the Northeast and Pacific Northwest of the U.S. In some poorer nations, the season for malaria-spreading mosquitoes has gotten longer since the 1950s.
The research also found that 72 percent of countries saw an increase in exposure to wildfires. And in 2020, up to 19 percent of the world's land surface was affected by extreme drought.
In the U.S., heat, fire and drought caused the biggest problems. The Pacific Northwest and Canada saw extreme heatwaves this summer. An earlier study found that the heat waves would not have happened if not for human-caused climate change.
Dr. Jeremy Hess, a professor at the University of Washington co-wrote the Lancet report. He said he saw the impacts of climate change while working at Seattle hospitals during the heatwave.
"I saw paramedics who had burns on their knees from kneeling down to care for patients with heatstroke," he said. "And I saw far too many patients die" from the heat.
The report said 65 of the 84 countries included help pay for the burning of fossil fuels, which cause climate change. Dr. Richard Jackson is a UCLA public health professor who was not part of the study. He said doing that "feels like caring for the desperately ill patient while somebody is handing them lit cigarettes and junk food."
"Code Red is not even a hot enough color for this report," said Dr. Michele Barry, a Stanford University professor who was not part of the study project.
She added, "we're going completely in the wrong direction."
I'm Dan Novak.