The ocean hasn’t been this warm in at least 12,000 years. El Niño is about to rewrite the world’s weather systems. It has us planning for what comes next, which has us thinking back to 1997 – a huge El Niño year.

It started with a swell of warm water that hurtled across the equatorial Pacific, bringing floods to Peru, droughts and wildfire to Indonesia, and a ceaseless downpour in East Africa. For the first time in the history of this enigmatic weather phenomenon, scientists watched it all play out in real time across a network of buoys and satellites, strung across the Pacific.

One of us watched it happen under a microscope.

Marco was peering at a slide in his university lab, and what he saw alarmed him. He was counting micro-organisms at the base of the ocean’s food chains. It didn’t take him long – there were barely a quarter of them left, and the ones that remained were smaller than they should have been. In one year, an entire marine food chain had fallen apart.

It was a symptom of a larger collapse. From Galápagos sea lions to penguins and Peru’s anchoveta – the largest fishery on Earth – the food web along the west coast of South America had unraveled. These were ecosystems that had never fully recovered from another record El Niño 14 years earlier. It was, in a sense, a relapse – a body still healing from one illness, hit by a second one while still recovering. 

Years later, on the cusp of this El Niño set to break every record, we find ourselves talking about that story again.