Climate change is already harming human health in ways that are “far worse than previously understood,” according to a new report in The Lancet, a prestigious British medical journal.

"Climate change is happening, and it's a health issue today for millions worldwide,” said Anthony Costello, co-chair of The Lancet Countdown, the commission that produced the report.

Heat waves, extreme weather, climate-related diseases and air pollution are already taking a significant toll on global public health, according to the report’s authors, who call climate change’s effects "unequivocal and potentially irreversible."

The report says that human-caused global warming “threatens to undermine the past 50 years of gains in public health.”

Based upon the findings of scientists, economists, mathematicians and engineers from two dozen universities and intergovernmental organizations, the report monitors 40 indicators of how climate change impacts health.

Hardest hit: lower-income countries, where adequate water supplies are threatened by drought, heat waves and housing destroyed by weather disasters is often uninsured and diseases worsened by warming temperatures – such as dengue fever – are claiming more victims than in the past. These countries also suffer greater economic loss than as a proportion of their gross domestic product because of climate-related disasters than higher-income countries.

Among the findings:

• From 2007 to 2016 there was a 46 percent increase in deaths related to floods, storms and other weather disasters compared with the decade between 1990 and 1999.
• Between 2000 and 2016, 125 million vulnerable adults were exposed to heat waves – a significant increase from previous years. While temperatures are increasingly globally, they are rising more rapidly in urban areas and affecting babies, the elderly, and people with chronic diseases in particular.
• Outdoor labor in rural areas has been severely affected by weather, with productivity decreasing by 5.3 percent over the past 16 years due to heat stress.
• Thousands of U.S. “climate change migrants” in Alaska and Louisiana have had to abandon their permanently due to rising waters; some have received federal funds to help them relocate.
• Among the few hopeful notes in the report: more countries are shuttering coal-fired power plants, whose carbon emissions contribute heavily to global warming.

The report’s authors are calling on public health professionals to become more active in pressuring governments and policy makers to take steps to combat climate change.

"If governments and the global health community do not learn from the past experiences of HIV/AIDS and the recent outbreaks of Ebola and Zika viruses," the authors warn, "another slow response will result in an irreversible and unacceptable cost to human health."