President Donald Trump is making good on his campaign promise to pull the US out of the Paris climate agreement — a move that’s been called a moral disgrace and that’s expected to hinder much needed progress in the fight against global warming.

A failure to tackle climate change will mean more extreme weather, dirtier air and water, and more food shortages. It’ll also mean more disease.

Researchers have long been arguing that the effects of climate change could undermine the last 50 years of gains in global health, increasing the spread of infections like yellow fever and chronic diseases like asthma and heart disease. Now is not the time to be scaling back efforts to reduce greenhouse gas emissions.

The December 2015 agreement, which has been signed by nearly 200 countries, aimed to cut greenhouse gas emissions and keep global warming below 2 degrees Celsius. (The US had committed to cutting its emissions by up to 28 percent from 2005 levels by 2025.) These goals were widely viewed as a win for public health. America’s retreat now could be a major setback.

Climate change is increasing the risk of epidemics

There are a number of ways climate change puts us at a greater risk for disease. Chief among them: a warmer planet is one that’s more hospitable to disease.

Disease-carrying vectors like mosquitoes thrive in warm and moist environments. Zika, dengue, and chikungunya are all spread by the Aedes type mosquito. And one of the reasons researchers think Aedes may be reaching new places — and more people — lately is climate change.

It’s not just mosquitoes, though: Bird flu, cholera, Lyme disease, salmonella — researchers believe all are being made worse by climate change.

At a February meeting on climate change and health, former Vice President Al Gore focused his talk on this problem. “Climate change is tilting the balance, disrupting natural ecosystems and giving more of an advantage to microbes,” he said. “Changing climate conditions change the areas in which these diseases can take root and become endemic.” (Read Maryn McKenna’s New York Times story for more on this.)

In addition, deforestation and urbanization are moving humans into areas where they haven’t lived before, and putting them into closer contact with animals that carry disease-causing microbes — like bats during West Africa’s 2014 Ebola outbreak. Brian Deese, a senior adviser to President Barack Obama overseeing climate change and energy policy, and former Ebola czar Ron Klain explained why in a piece at the Washington Post:

Climate change destroys habitats and stresses animal populations such as the bats of West Africa, forcing them to hunt for food nearer to humans. Humans, likewise pressed by climate impacts, encroach more closely on animal habitats. While we cannot know that climate change was the cause of the specific interaction between bats and humans that is believed to have launched the Ebola outbreak in Guinea, we will see more of these interactions in the future, and more epidemics as a result. Ebola demonstrates that even localized dislocation of people and animals can create global risk. Climate change is a threat multiplier for much broader dislocation — accelerating the complex factors that drive people from their homes.

Air pollution wreaks havoc on human health

Greenhouse gases are not only harmful to the environment — they also increase the risk of everything from asthma to heart disease.

According to the Global Burden of Disease project, more than 5 million people die worldwide each year because of air pollution, and emissions from coal-fired plants are a major risk factor here. It’s one reason why health experts have been pushing policymakers to rapidly phase out of coal.

For miners, the immediate health risks include black lung disease and scarring of the lung tissue. But the pollutants emitted when coal is processed — including sulfur dioxide, particulate matter, nitrogen oxides, and mercury — have much more far-reaching effects on many more people.

In one large study involving 450,000 Americans followed between 1982 and 2004, researchers found that increased exposure to the particles in fossil fuel emissions increased the risk of death from heart disease — and particles from coal burning were five times more damaging than other similar particles.

Reducing emissions from coal-fired power plants makes it easier to breathe. Over the past 30 years, the percentage of Americans with asthma has more than doubled, and climate change has been a significant driver of that trend. Air pollution triggers asthma attacks, contributing to lung abnormalities, particularly in the developing pulmonary systems of children.

The Paris agreement was no panacea — but it nudged the world in the right direction. Now, the US moves backward. It’s not just the future of the environment that’s at stake here. Our health hangs in the balance, too.