Back in 2015, more than 200,000 saiga antelopes mysteriously died in Kazakhstan over a three week period, wiping out 60 percent of the global population. Now, more than two years later, scientists think they finally know why.

In a paper published in Science Advances, an international team of researchers suggests that a disease called hemorrhagic septicemia is likely to have caused the mass mortality event (MME), triggered by conditions that can be associated with climate change. More than ever, it’s a stark reminder of the drastic effect humanity is having on the planet.

“I’ve seen large mortalities in my career, but this was very unique, unprecedented in large mammal groups I’ve worked with,” Richard Kock from the Royal Veterinary College in London, the lead author on the study, told IFLScience.

Taking samples from some of the dead animals, the team believe the cause of the disease was the bacterium Pasteurella multocida type B. Although this is found in both healthy and dead animals alike, under certain conditions it can lead to fatal conditions. This is an idea that's been touted before, but this paper rules out other possible factors.

Those conditions, the triggers for this MME (and likely two others in 1981 and 1988), were unusually high humidity and temperature in the days prior to the sudden die-off. The humidity threshold was deemed to be about 80 percent, with an average over the region of 84.6 percent. About 6°C (43°F), meanwhile, was the trigger for the temperature.

Combined, these conditions allow for massive multiplications of the bacteria in the bloodstream of the saiga. This produced toxic effects, shutting the bodies of the antelopes down before they had a chance to do anything. Within five hours they were dead.

“It’s like flies dropping,” said Kock. “The immune response is totally inadequate. The bacteria overwhelms it, it’s something the animal is not evolved for.”

Many of the dead antelopes were found spread apart from each other, suggesting they had died while still grazing. The calves, meanwhile, had died after drinking milk from their mother that was contaminated with the bacterium. Mortality rates were 100 percent.

All this appears to be associated with climate change-induced increases in temperature. This MME cannot be directly linked to climate change yet, but there seems to a pretty obvious breadcrumb trail leading us in that direction.

“This may illustrate the possibility that changes in environment can affect pathogen dynamics,” said Kock.

Saiga are shy animals, so we are unable to treat them with vaccines to prevent this happening again, but livestock and veterinary management could be helpful. More than ever, though, this event shows the terrifying effects man-made climate change can have on the planet. And we can definitely do something about that.