Climate change poses an emerging global health crisis with impacts that will only worsen as the planet continues to warm, a group of international health experts wrote Wednesday in a global assessment for The Lancet, a prominent medical journal. They warn that the world’s slow progress in reducing greenhouse gas emissions is putting lives and the health care systems people depend on at risk.

The report, a collaboration by leading doctors, researchers and policy professionals from international organizations including the World Health Organization, says heat waves and infectious diseases pose two of the greatest immediate threats, particularly for outdoor workers, elderly people in urban areas, and other vulnerable populations.  

The conclusions reinforce many of the findings spelled out in the Fourth National Climate Assessment, released last week by 13 U.S. government agencies.

“Climate change is a dire health crisis,” said Renee Salas, an emergency medicine physician at Massachusetts General Hospital and author of a U.S. policy brief that accompanied the Lancet report. “If we don’t start taking these preventative measures, mitigating the greenhouse gas pollution that is choking us every day, many more Americans will continue to suffer and die.”

The “Countdown” report, Lancet’s second annual look at the health impacts of climate change, analyzed dozens of health indicators around the globe. Its top conclusions:

• Changes seen today in the spread of vector-borne disease, work hours lost to excessive heat, and loss of food security provide early warnings of the “overwhelming impact” on public health expected as temperatures continue to rise. The impacts of climate change present “an unacceptably high level of risk for the current and future health of populations across the world.”
   
• Failure to reduce greenhouse gas emissions and adapt health care to climate change threatens human lives and the viability of the national health systems they depend on, with the potential to “disrupt core public health infrastructure and overwhelm health services.”
   
• How countries respond now to climate change will play a key role in shaping human health for centuries to come.
   
• Health professions can help hasten the response to global warming by ensuring a widespread understanding of climate change as a central public health issue.

The report found that 153 billion work hours were lost in 2017 due to extreme heat, a leading symptom of climate change and a significant increase from 2000. In India, the loss was equivalent to an entire year’s work for 7 percent of the country’s total working population.

The number of vulnerable people subjected to heat waves increased by 157 million people from 2000 to 2017, and rising temperatures also fueled the spread of infectious diseases including malaria and dengue fever, the report said.

“Outside the craziness of D.C., in the real world you don’t have to look very far to see that climate change is real,” said Gina McCarthy, a former administrator of the U.S. Environmental Protection Agency and director of the Center for Climate, Health and the Global Environment at the Harvard School of Public Health, who served as an advisor for the U.S. policy brief. “It threatens our health and our safety today.”

Health professionals are seeing new risks to human health, include antibiotic-resistant bacteria, impaired cognition for students in overheated classrooms, and mental health problems including increased suicide, Salas said.

Another emerging concern is the potential for increased carbon dioxide levels in the atmosphere to reduce the nutritional quality of crops that people rely on for food. “The potential impact of that is incredibly large,” said Kristie Ebi, a professor of global health at the University of Washington and an author of the report. There could be “hundreds of millions of people potentially affected by that change.”  

Lyndsay Moseley Alexander of the American Lung Association said the report “helps to highlight that, because we are not taking action to reduce all of the pollution that comes, for example, from coal-fired power plants, we are suffering the health impacts now.”  

The report notes, for example, that from 2010 to 2016, air pollution concentrations worsened in almost 70 percent of the world’s cities. In 2015, pollution involving fine particulate matter resulted in more than 2.9 million premature deaths, it said.

Alexander served as a reviewer for the package’s U.S. policy brief, which called for increased funding for the health care sector to address issues related to heat waves and the spread of infectious disease. It also called on hospitals and other health care facilities to transition to renewable energy and divest from fossil fuels.

“The news seems grim,” said Juanita Constible, a senior advocate for climate and health with the Natural Resources Defense Council, “but we actually have the power to make the future we want rather than just accept that future that we are currently on track for.”