As the planet heats up, an increase in wildfires, extreme heat, and drought is upending millions of lives worldwide, according to a new report from public health leaders around the world, putting the planet on the precipice of a global epidemic that could dwarf the COVID-19 crisis.

The report, published Wednesday in The Lancet, details how little progress has been made to protect the world’s population from the health impacts of climate change, despite years of scientific reporting on the impacts of the crisis.

As international leaders prepare to meet in Glasgow for the next round of global climate negotiations — talks that few expect to result in the dramatic emissions cuts that experts say are needed — the report calls on negotiators to take aggressive action to shift off fossil fuels.

“Global leaders will have an opportunity at COP26 — perhaps the last opportunity — to really move things and tackle the climate and health crisis,’’ said Anthony Costello, a former director of the World Health Organization and a co-chair of the Lancet Countdown report. “All countries must commit to much more ambitious climate plans that incorporate health, equity and societal support.’’

At the Glasgow climate talks, negotiators will be working to put the planet on a path to constrain warming to 1.5 degrees Celsius above preindustrial times. But according to a United Nations report, the current pledges from countries would cause temperatures to rise as much as 2.7 degrees Celsius by allowing emissions from fossil fuel burning to increase 16 percent this decade. To prevent catastrophic warming, according to the UN report, emissions must be on a steep decline during that period.

As the Lancet report explains, the health impacts have been severe already, with the world at 1.1 degrees Celsius of warming. This is the sixth annual Lancet Countdown report, which represents the consensus of leading researchers from 43 academic institutions and UN agencies and which tracks progress along 44 indicators of climate change and health.

Around the world, 2 billion people in 2019 were affected by food insecurity, which is being fueled by extreme drought due to climate change, the report said. Meanwhile, the potential for outbreaks of dengue, chikungunya and Zika is on the rise, and the coasts around northern Europe and the US are becoming ripe for bacteria that can lead to gastroenteritis, severe wound infections, and sepsis.

The report noted that more than a million people died in 2019 due to exposure to air pollution from the burning of fossil fuels.

A likely rise of infectious outbreaks is especially dramatic along the northeastern coast of the US, where the area of coastline suitable for transmission of Vibrio bacteria — which can be contracted via oysters — has increased by 25 percent since 2011, according to the report.

In a Lancet briefing focused on health impacts in the US, a group of health experts from 70 leading US institutions, organizations and centers looked at how the rise in drought, wildfires, and extreme heat is leading to illness and death, especially among specific groups — like people of color, outdoor workers, incarcerated people, and those living below the poverty line — that are made more vulnerable due to historic redlining and a lack of workplace protections.

“Climate change harms my patients in broad ways, and it can be minor to severe,’’ said Renee Salas, a lead author of the US report and a fellow at the Center for Climate, Health, and the Global Environment at the Harvard T.H. Chan School of Public Health.

In her emergency medicine practice at Massachusetts General Hospital, Salas said she sees it in the increase of allergens causing her patients to have more frequent asthma attacks, or in the spread of waterborne illnesses that can cause vomiting or diarrhea. She sees it in life-threatening heatstroke, or breathing troubles exacerbated by air pollution from wildfire smoke.

Climate change — like the COVID-19 crisis — has made the inequities between higher-income and lower-income countries clearer than ever, the Lancet report said. Although the wealthiest countries have made the most progress toward cutting emissions, the report’s authors write that they are still the main contributors of emissions, accounting for 45 percent of the global total.

Further, of the 84 countries that account for 92 percent of global carbon emissions, as of 2018, 65 were still subsidizing fossil fuels, the report noted.

The trillions of dollars of COVID recovery money worldwide could represent an opportunity to invest in climate mitigation, the reduction of inequities and the safeguarding of health, the report says.

Failing to take steps to prepare for a climate-related health crisis could invite the kind of chaos seen in the early months of the pandemic, when “quite frankly, we were not prepared,’’ said Georges Benjamin, the executive director of the American Public Health Association. “We did not put the infrastructure in place that needed to be in place, we de-invested in our health and public health systems in ways that quite tragically resulted in two years of a significant outbreak that did not have to be as bad as it was.’’

Now, he said, “We’re about to do the same mistake again.’’

Massachusetts, where Governor Baker has proposed a third of its $5.3 billion in federal relief dollars be directed to climate-related work, may represent an outlier, as other parts of the world include additional subsidies for fossil fuels in their recovery plans, according to the report.

“If we fail to do what we need to do to limit warming, it will be catastrophic for public health,’’ said Salas, who will be attending the Glasgow climate talks.

Reach Sabrina Shankman at sabrina.shankman@globe.com. Follow her on Twitter @shankman.