Tardigrades are arguably the most resilient creatures in the known universe — and even they might not be able to live through global warming.
The micro-animals colloquially known as "water bears" are capable of entering a state of suspended animation, bringing their own metabolic activities almost to a halt in response to environmental stressors.
In this death-like state, tardigrades can survive for years in extreme environments, including the vacuum of space. However, a new study out of Denmark has found something tardigrades can't survive: long-term exposure to high temperatures.
"We had found their Achilles' heel," researcher Ricardo Neves, from the University of Copenhagen, told Newsweek. "Tardigrades are definitely not the almost indestructible organism as advertised in so many popular science websites."
For the study, published in the journal Scientific Reports, the researchers sourced a species of tardigrade called Ramazzottius varieornatus from rain gutters in Denmark. They then coaxed some of the critters into one of their states of suspended animation called "desiccation," which they enter in response to a lack of water in their environment, and left others active.
When the scientists exposed the active tardigrades to a temperature of 37.1 degrees Celsius (98 degrees Fahrenheit) for 24 hours, 50 percent died. If exposed to lower temperatures first and given time to acclimate, the active tardigrades didn't hit that 50 percent mortality threshold until 37.6 degrees Celsius (99.7 degrees Fahrenheit).
As for the desiccated tardigrades, 50 percent died after one hour at 82.7 degrees Celsius (180.8 degrees Fahrenheit). The maximum temperature 50 percent could withstand for 24 hours was 63.1 degrees Celsius (145.5 degrees Fahrenheit).
"The fact that the median lethal temperature for active R. varieornatus is so close to the median maximum temperature in Denmark — where the specimens used in this study have been sampled — is quite worrying in our opinion," Neves told Newsweek, adding that "it seems that even tardigrades will have a hard time handling rising temperatures due to global warming."
Still, while it's undeniably troubling that the practically indestructible tardigrade's kryptonite is the very thing now threatening our own existence, it is worth reiterating that the desiccated tardigrades' temperature threshold was far higher than Earth's current average.
Scientists believe an increase of just 2 degrees Celsius (3.6 degrees Fahrenheit) over pre-industrial levels could push humanity to the point of extinction. But 50 percent of desiccated tardigrades could survive an increase of more than 25 degrees Celsius (45 degrees Fahrenheit) for at least 24 hours, and maybe longer.
Maybe the stress of extreme climate change will force some surviving tardigrades into one of their states of suspended animation — where they can try to outlast humans, and perhaps even climate change, entirely.
READ MORE: Tardigrades Are Basically Indestructible, But Scientists Just Found Their Weak Point [ScienceAlert]
More on tardigrades: Crashed Moon Lander Splattered Live Organisms Onto Lunar Surface
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