The Great Dying—it was the largest mass extinction ever, destroying more than 96 percent of all marine life and 70 percent of land dwellers. But what caused this 252-million-year-old, Permian-era event? Scientists have long suspected global warming but had failed to make a concrete connection. That changed in December 2018, when University of Washington grad student Justin Penn, collaborating with UW academic advisor Curtis Deutsch and a team at Stanford University, published work revealing how rising temperatures were directly responsible for the Great Dying. And given today’s increasingly toasty planet, their findings have terrifying implications for future globe-spanning catastrophes. Don’t descend to your doomsday shelter just yet though. Penn, an LA native, says while the problem is complex—and existential—a solution, however unpopular, exists. —JV

My whole life I’ve been interested in pursuing truth, whatever that means. Trying to understand the world that we live in.

I studied abroad in Costa Rica [as an undergrad at UCLA]. Our classroom was the forest and the beach, so that got me interested in biodiversity and conservation. 

I came back that summer and I wasn’t paying attention to what classes I had to sign up for. I missed all the deadlines. There was one still open: Chemical Oceanography with Curtis Deutsch, who was also at UCLA when I was there. I was like, Oh man, this sounds so dull.

The first day Curtis started talking about how to understand the ocean, you need to bring methods from physics and chemistry and biology and geology—all of the fundamental sciences. And I was like, Oh shit, this is the subject for me.

We know the earth has undergone major extinction events in its past, and they seem to have been related and correlated in time with climate change events.

But the exact cause connecting that climate change to extinction has been fuzzy.

What our study has done is make the connection between warming itself and the loss of oxygen from ocean water and the actual collapse of the marine ecosystem 250 million years ago.

We use mathematical models to tell us what environments looked like at any given point in time.

We can predict where the species could live and where they couldn’t, and how many would have gone extinct because of warming and oxygen loss.

The rock record records both the environmental changes and the response of the ecosystem to those changes. By testing [our] model against the fossil record, we were able to say that the causes of the extinction were global warming and the loss of oxygen from the ocean.

By the end of the next century, if we just keep emitting CO2 at the same rate, we’ll get to about 20 percent of the warming magnitude. And if we keep doing it to the year 2300, then the warming magnitude increases to between like 35 and 50 percent of what caused the [Great Dying] extinction.

Science is useful as a means to identify why things are happening in the world.

Like, why is the world getting warmer? If we know—which we do—that global warming is caused by human emissions of greenhouse gases into the atmosphere, then we know what the solution to the impacts of global warming on life is. And that is to stop emitting greenhouse gases.

To intentionally misquote John Lennon, ‘Extinction is over! If you want it.’