This post was created for ClimateProgress.org, a project of the Center for American Progress Action Fund.  Joseph Romm is the editor of Climate Progress and a senior fellow at the Center for American Progress.

Just in time for the summer mosquito season, the Natural Resources Defense Council (NRDC) released a report last week detailing the latest climate-based threat to human health.

The two mosquito species capable of carrying dengue fever are rapidly spreading across the southern United States, increasing the incidence of the disease. We already knew that “Climate change is the biggest global health threat of the 21st century” – now, it seems, we’re reaching the point where “threat” turns into “harsh reality.”

The report tells it straight:

Global warming threatens to further exacerbate the spread of many infectious diseases because increases in heat, precipitation, and humidity can foster better conditions for tropical and subtropical insects to survive and thrive in places previously inhospitable to those diseases.

And, as the NRDC discusses in its report, dengue fever is top among those diseases. Also known as “breakbone,” dengue causes “fever, severe headache, backache, joint pains, nausea and vomiting, eye pain, and rash.” The Center for Disease Control (CDC) warns that, “if unrecognized and not properly treated,” dengue can develop into dengue hemorrhagic fever (DHF) and possibly kill its host. Unpleasant, right?

Once considered exclusive to the tropics, dengue has experienced a 30-fold increase in incidence rates during the last 50 years and has since spread to more temperate climates, now including huge swaths of the United States.

While previously limited to the United States-Mexico border, the Aedes aegypti and Aedes albopictus mosquitoes have now spread to 28 American states (check out the map), threatening an estimated 173.5 million Americans, particularly in the southern and mid-Atlantic regions. The report describes how climate change exacerbates the situation:

Warmer temperatures boost the speed of development of adult mosquitoes, increasing their numbers. Female mosquitoes bite more frequently in hotter temperatures, and warmer winters enable mosquitoes to survive in areas that were formerly too cold. Higher temperatures also shorten the time it takes for the virus inside the mosquito to develop and become infective.

Worldwide, about 2.5 billion people live in areas threatened by the mosquito species that can carry dengue. NRDC projects this number to increase to 5.2 billion people by 2085, and as America’s climate becomes more tropical (see: “Our hellish future: Definitive NOAA-led report on U.S. climate impacts warns of scorching 9 to 11°F warming over most of inland U.S. by 2090”), a larger and larger proportion of that 5.2 billion will be Americans.

In short, climate change produces ideal breeding grounds for mosquitoes and the diseases they carry in once-safe, once-temperate regions. This puts hundreds of millions of Americans and billions of people worldwide at increased risk of contracting dengue, among other diseases; in regions with weak medical services, they face the possibility of death.

Unless we shift course soon, “desperately fighting deadly mosquitoes” could become the next major green job. How about we act now, stop climate change at a minimal cost, and actually save lives?

Austin Davis is a summer intern at American Progress, working on climate, energy and clean economy issues. Austin is pursuing a BA in political science at Middlebury College.