A child born today faces two possible futures. In one, the world continues to burn fossil fuels, making the child more likely to develop asthma from air pollution, at greater risk of vector-borne diseases, and more vulnerable to anxiety as extreme weather events threaten his community.

In the other, those risks are diminished because the world has responded quickly and adequately to climate change, with a large-scale shift away from fossil fuels.

These two, starkly different paths are the focus of a report published Wednesday by the medical journal The Lancet that shows how the future health of a child born today will be intrinsically linked to climate change, from the womb to adulthood.

“Without accelerated intervention, this new era will come to define the health of people at every stage of their lives,” the authors write.

In the latest update to the Lancet Countdown—an ongoing study of the impacts of climate change on health—100 experts from around the globe write that the world’s response to climate change will dramatically alter the lives of children.

Climate change is already impacting public health. The warming already observed worldwide has created a climate that is more suitable for disease transmission, less productive for crops and more prone to extreme weather than ever before. Nine of the 10 most suitable years for the transmission of dengue fever have occurred since 2000. Air pollution, primarily driven by fossil fuels and made worse by climate change, caused about 7 million deaths in 2016.

But that doesn’t compare to what’s in store, the authors write. With a global average life expectancy of 71 years, a child born today could experience a world that has warmed 4 degrees Celsius (7.2°F) above preindustrial temperatures if greenhouse gas emissions continue at a high rate.

“We roughly know what that looks like from a climate perspective,” said Nick Watts, a medical doctor and the executive director of the Countdown. “We have no idea what it looks like from a public health perspective, but we know it is catastrophic. We know it has the potential to undermine the last 50 years of gains in public health and overwhelm the systems we rely on.”

The update to the Lancet Countdown examines 41 indicators of climate change—from heat extremes to the spread of vector-borne diseases to how health systems are responding to global warming. This is the fourth update to the Countdown, which was first published in 2015, and is the result of work from 35 academic institutions and UN agencies across the world, drawing from climate scientists, engineers, economists, political scientists, public health professionals and doctors.

There’s one notable departure from earlier versions of the report: “This is the first time we feel we can say these health impacts have arrived in full,” Watts said. “A while ago you’d see the fingerprints of climate change over a heat wave and that’d be it. Or small parts of vector-borne diseases. The more we look now, the more we see it everywhere.”

This year’s update also has a focus on the inequity of climate change.

“While climate change threatens the health of everyone, it harms some of us more,” said Renee Salas, an emergency medical doctor who was the lead author of the U.S. policy brief associated with the Countdown. “With every degree of warming, a child born today faces a future where their health and well-being will be increasingly impacted by the realities and dangers of a warming world.”

Threats at Every Stage of Childhood

The threat begins in the womb, where extreme heat and air pollution have both been found to contribute to low birth weights and neonatal deaths, said Salas. “If a child is born, they remain especially vulnerable to heat-related illness. Their bodies are not able to regulate temperatures as well as adults,” she said.

With less developed immune systems, infants and young children are at a higher risk for certain water- and food-borne illnesses. They’re also more likely than adults to develop asthma as a result of exposure to air pollution, or have existing asthma symptoms exacerbated.

As a child reaches adolescence, there are new concerns to worry about, like longer or more intense heat waves leading to heat stroke for student athletes, or the mental health impacts of extreme weather events. One study included in the U.S. brief found that students who are in a hot building have an impaired ability to think.

“This also gets into the equity issue. Which students are in the schools without air-conditioning?” said Salas. “Imagine a world where students are going to have a bit more difficulty learning essential information.”

As a doctor, Salas said she’s concerned about what all this trauma adds up to. “We don’t understand yet what these cumulative impacts mean over the course of the life,” she said. “Especially given the catastrophic health impacts that we’re concerned about in the future. We need to better understand climate change as a threat multiplier on so many levels.”

But there’s another option, too.

“It turns out that when you look at all the things we want to do to respond to climate change, many of them are just cost-effective, sensible public health interventions in their own right,” said Watts.

A child born in the United Kingdom today will see a dramatically different world, based on the current pledges to combat climate change. “By their sixth birthday, we would see a complete phase-out of coal. That means that they may not know what a coal plant looks like,” he said. That’s true for 32 other countries around the world.

By the time that child turns 21, if they’re in Western Europe and the world has made good on its climate pledges, they won’t be able to buy a vehicle that burns gas or diesel fuel. For those living in urban areas, “if we’ve done it right, they won’t want a car at all. They will be living in more livable cities, healthier cities. They will be cycling, walking to work, because we will have the infrastructure to support that.”

By the time they are 31, “the world will have reached net zero” emissions, he said. “Healthier diets, cleaner air, more livable cities.”

What Can Be Done?

Though the report lays out a scary future, it also presents a host of things that can be done to combat the twin issues of health risks and climate. Those include decreasing planet-warming greenhouse gas emissions, by phasing out coal and increasing the amount of electricity generated from renewable sources, and decarbonizing the agriculture and healthcare sectors.

But not all the indicators are trending in a positive direction, the report notes. Though coal supplies had been declining from 2014 to 2016, they have since begun to increase. “The year 2020 is important for two reasons,” the report notes. “It is the year that the implementation of the Paris Agreement begins, and the year during which most studies suggest global emissions must peak to remain on the path to achieving the 1.5°C goal.”

Gina McCarthy, the former head of the EPA under President Obama, said the recommendations in the report for how to adapt and mitigate climate change are crucial.

“If you look at what we can do at the state and local level today, we can make remarkable progress,” said McCarthy, who was newly named to lead the Natural Resources Defense Council. “In the electricity sector, by moving to renewable energy that’s cheaper, by looking at low emission vehicles, by looking at our transportation corridors—that we cannot just reduce air pollution but provide opportunities to expand those corridors, to look at biking and walking, to get people healthy again.”

It’s About ‘Survival of Our Civilization’

One of the challenges, the experts acknowledge, is taking the conversation out of the political realm and into the personal.

“We need people to be hopeful about climate change,” McCarthy said.

“These very scientifically vetted issues are reduced to political currency and a political currency that creates divisiveness and things don’t get done,” said former Surgeon General Richard Carmona, who was not part of the report. “We have to move beyond that. We have to elevate the discussion to one of truly the survival of our civilization as we move forward.”