A lot can happen in two years.

Elections cycle every two years. A baby elephant goes from a tiny speck to a 200-lb animal walking on land. E-bikes went from a niche to covering the lakeshore.

In the last two years, a lot has happened. In March 2020, the World Health Organization declared a global pandemic when a new, slippery coronavirus spilled out from the nasal passages of pangolin or a raccoon dog into the airways of COVID-19 patient zero in a wet market in Wuhan, China. The highlight reel from the next 24 months include global social distancing, daily life upended, the fastest-ever created vaccine, more infectious variants, and a reckoning that those who are most vulnerable are often the least protected.

But this wasn't the first pandemic we encountered—nor will it be the last. And the ones in the future have the potential of being much different than the ones we've faced before.

In its Epidemics and Their Aftermath theme, Science News' Century of Science tackles epidemics (a pandemic is worldwide, while an epidemic isn't). From explosive pandemics like the 1918 flu and COVID-19 to the thousand years-long epidemic of tuberculosis infections, people aren't strangers to infectious diseases.

Most epidemics read like a list of who's who of the bacteria and virus world. Tuberculosis? Bacteria. Smallpox? Bacteria. COVID-19? Virus. Influenza? Virus. But there's another infectious pathogen slowly gaining traction as our world starts to warm – fungal infections.

Like any microorganism, some fungi are harmless. They cluster on plant roots to help the plant soak up nutrients. They're essential in baking bread and in brewing beer. Other fungi, though, can infect our bodies and make us very, very sick, especially those who already have compromised immune systems.

As the COVID-19 pandemic entered its second year in 2021, a rare fungus called mucormycosis kicked off a simultaneous epidemic in India. This "black fungus" was infecting the sinuses, eyes and even brains of COVID-19 patients, whose immune systems were already in a tizzy fighting the virus. Left untreated – and the treatment is long and difficult – black fungus can kill up to half the people who contract it.

Treatment for fungal infections is hard because, unlike bacteria and viruses, humans and fungi share similar biology. So whatever medications we use to fight a fungal infection will also harm our cells. Alarming news, since fungal infections are anticipated to increase because of our warming world.

As the world gets warmer, fungi are adapting quickly to the warmer temperatures, broadening the places they can live. Candida auris, a cousin to the yeast that helps bread rise, has emerged as a pathogenic threat with outbreaks erupting around the world. Scientists think that Candida acclimated to warmer temperatures in the environment which now let it survive within the human body – a place that used to be far too warm for the fungus.

With the climate crisis continuing, the threat of fungal epidemic continues to grow. And as we've learned with COVID-19, a single infection can spread like wildfire if the conditions are right. While we have lots of experience from previous epidemics, new ones with new foes will test us in new ways.