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By midcentury, an emerging public health problem will change how we eat and travel and even determine where we live.

World leaders are discussing it for the 20th time beginning today in Paris.

It’s climate change, and it’s is happening so fast it’s prompted the BMJ to write a letter to the World Health Organization recently urging them to declare the phenomenon a public health emergency.

But we shouldn’t lose hope just yet.

As the authors of a large recent paper in the British medical journal The Lancet argue, “tackling climate change could be the greatest global health opportunity of the 21st century.”

Here’s how:

1. We could stave off hundreds of thousands of deaths and illnesses from respiratory disorders

Ever wonder why smog always seems so much worse on a hot, sunny day? Your eyes aren’t playing tricks on you. The chemical reactions that form ozone — one of smog’s main components — happen faster at higher temperatures.

The warmer it is outside, the more ozone gums up the air. Ozone doesn’t just dirty the horizon, though. The toxin also exacerbates a host of respiratory conditions (from asthma to bronchitis and emphysema) by irritating the delicate tissue lining the lungs.

In recent years in some parts of the US, ground-level ozone has reached dangerous levels. Overall, though, the US is a partial success story for the pollutant: Ozone levels started to decline for the first time here in the 1980s.

Ozone levels are still on the rise in other parts of the world, however, leading to more complications and even deaths from respiratory conditions that could have previously been treated. In India, levels of the pollutant were so high in 2014 that scientists estimated it killed enough crops to feed close to 100 million people in poverty.

2. We could prevent thousands of cases of heat stroke

Having a psychiatric illness like depression can more than triple your risk of dying during a heat wave.

First, depression can make it harder to take the necessary steps to protect oneself from changes in the environment. People with depression already experience difficulties with self-care, such as staying hydrated, maintaining personal hygiene, and taking their medications consistently. High temperatures can make these activities especially taxing.

Worse still, people who take medications to treat mental illness are especially susceptible to heat stroke, a serious condition that results when the body overheats, because many mental health medications interfere with our body’s natural ability to regulate its temperature. Antipsychotics like Abilify and Risperdone, for example, block brain cells from communicating with the body’s thermostat, the hypothalamus. Anticholinergics, such as Cogentin and Enablex, inhibit sweating and make it easier to overheat.

3. We could curb the spread of infectious disease

Increased heat will expand the range of pests carrying deadly disease. In the past few years, mosquitoes carrying malaria (which killed 630,000 people last year) have already begun creeping up mountains to recently-warmed, higher-altitude elevations, where they spread malaria to areas never previously exposed to the disease.

Since they’ve never been exposed before, people living in these areas will have zero protective immunity from the disease. The result? Malaria will be deadlier than ever.

Mosquitoes, which thrive in warmer climates, also carry diseases like dengue and yellow fever, which collectively kill more than 50,000 people each year. As temperatures rise, more and more areas around the globe will become increasingly hospitable to the pests.

Bacteria, too, will take advantage of their newly-welcoming habitats.

Vibrio cholerae, the comma-shaped bacteria responsible for cholera, prefers to nest in warm, coastal seawaters. As recently as last year, however, the bacteria were discovered floating in usually cooler Baltic Sea that separates Central and Northern Europe. Cholera now kills between 100,000 and 130,000 people worldwide each year, almost entirely in areas where there is a lack of clean water. Warming waters means that the bacteria can live longer and spread to more locations. At one site in Bangladesh, cholera risk rose two to four fold in the six weeks after a 9-degree Fahrenheit spike in water temperature⁠.

4. We could prevent needless deaths from lack of access to water

Water scarcity is another emerging threat. Severe droughts have already begun plaguing the west coast of the US. In Tulare County, south of Sacramento, Calif., the board of supervisors has declared a state of emergency. People can’t flush toilets, wash clothes, fill cups, or bathe without buckets of bottled water that are driven in from elsewhere.

In other parts of the world, where crops that feed the rest of the globe depend on a steady stream of slowly-melting glacier water, water scarcity is an even more serious problem. The Himalayan glacier, for example, presently supplies 25% of the world’s cereal crop. If it melts too quickly, however — as some estimates suggest it has already begun doing — it will become nearly impossible to meet the needs of a growing, hungrier planet.

5. We could prevent hundreds of thousands of cases of starvation

With the exception of a few, the majority of the world’s crops will be ravaged by the new pests and diseases that take advantage of warmer temperatures.

Climate change is projected to drive down global food production by 2% every ten years, even as the demand for food increases by 14%. Across Africa and South Asia — regions where much of the world’s food is produced — yields of wheat, corn, and millet will fall nearly 10% by mid-century. As a result of this rocky imbalance, the price of rice and corn will skyrocket, likely doubling by 2050.

6. We could curb rising rates of anxiety and PTSD

In 2006, a team of psychologists visited thousands of victims of Hurricane Katrina — six months after the original event. They diagnosed nearly half of the residents they visited with a serious anxiety disorder. One in six, the doctors said, had PTSD, and many suffered from both illnesses. Over time, these disorders can lead to suicidal thoughts and, in some cases, suicidal behaviors.

In 2008, mental health workers returned to New Orleans. To their surprise, the number of people regularly contemplating suicide hadn’t fallen (as is usually the case after a natural disaster). On the contrary, the number of suicidal residents had risen significantly, along with the number of people with serious mental illness. Even in 2009, the number of suicides in New Orleans Parish remained double its pre-Katrina levels.

Because cases of mental illness and suicidal behavior increased in general in the years after the recession, which happened to coincide with the occurrence of Hurricane Katrina, it’s impossible to pinpoint Katrina as the sole driving force behind the huge uptick in mental illness here.

However, the pattern of increases in depression and anxiety after any severe natural disaster is well documented: The mental health infrastructure in Haiti nearly collapsed in the wake of the 2012 earthquake there; Typhoon Haiyan, the strongest tropical cyclone ever recorded to hit land, led to a spike in incidences of post-traumatic stress disorder among victims in the Philippines; and the 2011 East African drought in Somalia, Kenya, and Ethiopia caused existing psychosocial support networks in the region to crumble.

SEE ALSO: 22 devastating effects of climate change

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