For the first time, we have a detailed model of what happened to the atmosphere and the climate after the asteroid impact that led to the extinction of the dinosaurs.
Although dinosaurs were in decline before a giant asteroid made the Chicxulub crater, it is generally accepted that this cataclysm finished them off. Yet it hasn't been entirely clear how. Now, a paper in Geophysical Research Letters fills in that gap.
Knowing the location and approximate size of the asteroid of doom, Julia Brugger, a PhD student at the Potsdam Institute for Climate Impact Research, used climate simulators to model the atmospheric consequences of forests burning and so much material thrown into the atmosphere.
Brugger concluded that sulphates, rather than dust, thrown up by the asteroid impact did most of the climatic damage that killed off the dinosaurs. While other substances quickly rained back down, the sulfur became incorporated aerosols. As with similar material released in volcanic eruptions, these aerosols blocked sunlight from reaching the Earth.
With so much material in the skies at once, temperatures plunged. "It became cold, I mean, really cold," Brugger said in a statement. On average, global temperatures dropped 26°C (47°F). The tropics barely remained above freezing point and the average global temperature fell below 0°C (32°F) for around three years.
"The long-term cooling caused by the sulfate aerosols was much more important for the mass extinction than the dust that stays in the atmosphere for only a relatively short time," said co-author Dr Georg Feulner. "It was also more important than local events like the extreme heat close to the impact, wildfires or tsunamis."
Naturally, the ice-caps expanded, and even once the sulfates cleared, all that whiteness continued to cool the planet by reflecting sunlight back to space.
Just as human-induced warming is having an effect on ocean circulation, with potentially devastating consequences, the sudden bout of cold changed water movements, with effects that lasted long after the sulfates were gone. Surface waters cooled and sank, allowing nutrient-rich bottom water to rise. As sunlight returned, these nutrients would have created enormous and probably toxic algal blooms, with severe consequences for many surviving marine species.
It would have taken more than 30 years for the planet to return to something like normality, Brugger concluded. The disruption was so great, the surviving species are more surprising than those that didn't. The mammals who made it through the crisis to become our ancestors deserve respect.
Feulner noted: “[The study] illustrates how important the climate is for all lifeforms on our planet. Ironically today, the most immediate threat is not from natural cooling but from human-made global warming." Unlike the dinosaurs, we can mitigate and prepare.
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