Climate change is already having an impact on our health, by exposing people to dangerous heat waves and more extreme weather, according to a new study. And if countries and cities worldwide don’t address global warming urgently by reducing carbon emissions, switching to renewables and electric cars, for instance, things are only going to get worse.

The report, called The Lancet Countdown on Health and Climate Change, is meant to track progress on health and climate change worldwide. It’s the first analysis borne out of a collaboration between 24 academic institutions and international organizations such as the World Health Organization (WHO).

“The outlook is challenging.”

"Climate change is happening, and it's a health issue today for millions worldwide,” said Anthony Costello, co-chair of The Lancet Countdown and a director at the WHO, in a statement. “The outlook is challenging, but we still have an opportunity to turn a looming medical emergency into the most significant advance for public health this century.”

Our world is heating up: The planet has already warmed by roughly 2 degrees Fahrenheit since 1880, and if we don’t heavily reduce emissions of heat-trapping greenhouse gasses like CO2, experts fear that average global temperatures could increase by 9 degrees Fahrenheit or more by the end of the century. That would be catastrophic: Most scientists see a temperature increase of just 3.6 degrees Fahrenheit as the threshold beyond which climate change is irreversible and apocalyptic. A warmer world doesn’t only mean warmer temperatures. It means changes in rain, rising sea levels, and more extreme weather like strong, destructive hurricanes.

Although we often think of climate change as a far-off problem, it is already affecting our health — especially the health of vulnerable populations in developing countries. Here are some instances of how climate change is already a health issue today, according to the report:

Dizzy, faint, and unconscious

Heat stress. Between 2000 and 2016, the number of people exposed to heat waves increased by about 125 million, with a record 175 million more people exposed to heat waves in 2015. Excessive heat can make people dizzy, faint, and unconscious. It can also create kidney problems because of dehydration, and without medical help, it can kill. This makes children, older people, and people with health conditions particularly vulnerable to rising temperatures.

Between 2000 and 2016, the number of people exposed to heat waves increased by about 125 million, with a record 175 million more people exposed to heat waves in 2015. Excessive heat can make people dizzy, faint, and unconscious. It can also create kidney problems because of dehydration, and without medical help, it can kill. This makes children, older people, and people with health conditions particularly vulnerable to rising temperatures. Malnutrition. Since 1990, the number of people who are undernourished in 30 countries in Asia and Africa has increased from 398 to 422 million. Increasing temperatures and drought can affect crop production: Each 2 degrees Fahrenheit rise in temperatures reduces global wheat production by 6 percent, and rice grain yields by 10 percent.

Since 1990, the number of people who are undernourished in 30 countries in Asia and Africa has increased from 398 to 422 million. Increasing temperatures and drought can affect crop production: Each 2 degrees Fahrenheit rise in temperatures reduces global wheat production by 6 percent, and rice grain yields by 10 percent. Natural disasters. Between 2007 and 2016, there were on average 306 weather-related disasters per year, a 46-percent increase since 2000. Extreme weather — like flooding and hurricanes — can create a host of health problems. Floods, for instance, can cause the spread of water-borne and mosquito-borne diseases; hurricanes can destroy crops, leading to food insecurity; and flooding can impact water quality.

Between 2007 and 2016, there were on average 306 weather-related disasters per year, a 46-percent increase since 2000. Extreme weather — like flooding and hurricanes — can create a host of health problems. Floods, for instance, can cause the spread of water-borne and mosquito-borne diseases; hurricanes can destroy crops, leading to food insecurity; and flooding can impact water quality. Infectious diseases. The rate of transmission of some mosquito-borne infectious diseases has also increased. For instance, since 1950, the rate at which the Aedes aegypti mosquitoes spread dengue increased by over 9 percent. Dengue is a viral infection that can be fatal. Warmer temperatures can expand the range of mosquitoes — and the diseases they carry with them, such as malaria and Zika.

The rate of transmission of some mosquito-borne infectious diseases has also increased. For instance, since 1950, the rate at which the Aedes aegypti mosquitoes spread dengue increased by over 9 percent. Dengue is a viral infection that can be fatal. Warmer temperatures can expand the range of mosquitoes — and the diseases they carry with them, such as malaria and Zika. Mass migrations. At least 4,400 people have been forced to migrate worldwide because of climate change. That could be because of rising sea levels and coastal erosion, as well as food and water insecurity caused by droughts and heat. As many as 1 billion people could be forced to migrate by the end of the century, and that could lead to conflict. Wars and poverty are bad for the physical and mental wellbeing of the people involved.

“Potentially devastating impacts on wellbeing and mental health”

Economic problems. From 2000 to 2016, increasing temperatures have led to an estimated 5.3 percent drop in work productivity for people doing manual, outdoor labor in rural areas. That obviously has negative consequences for the livelihoods of these people, their families, and communities, especially for those who rely on farming for their living. Extreme weather has also caused an estimated $129 billion in economic losses in 2016. Almost all of these losses were uninsured in low-income countries, and that has “potentially devastating impacts on wellbeing and mental health,” the report says.

To better prepare for the health impacts of climate change, countries and cities should do risk assessments and have a plan of action. For example, making sure that hospitals and nursing homes are equipped to withstand extreme weather, flooding, and loss of power should be a priority. But health-adaptation funding accounts for only about 5 percent of total global-adaptation spending, the report says. Countries should also switch to more renewable forms of energy, as well as boost electric vehicles. The stakes are incredibly high.

“We must do better,” said Christiana Figueres, chair of The Lancet Countdown's High-Level Advisory Board, in a statement. “When a doctor tells us we need to take better care of our health we pay attention, and it's important that governments do the same.”