Energy & Environment

World is releasing greenhouse gases at level unprecedented in geologic history, scientist says

Editor’s note: This story has been updated to correct Michael Mann’s university affiliation.

Human civilization came to be thanks to the comparatively stable climate of the past 10,000 years.

But the unchecked burning of fossil fuels is undermining that foundation, according to a leading climate scientist.

“There is no analog in the past for the rapid warming” we are seeing today, University of Pennsylvania climate scientist Michael Mann argued.

In a speech Thursday at the “The Good, The Bad and the Wicked” climate conference, presented by the Meadows Center for Water and the Environment at Texas State University, Mann argued climate is the hidden factor in the history of life — and its many devastating extinctions.

The talk was drawn from Mann’s new book, “Our Fragile Moment: How Lessons from Earth’s Past Can Help Us Survive the Climate Crisis,” which will be released later this month.

In 1999, Mann published the famed “Hockey Stick graph” of the world climate system. The name conveys a long, largely stable climate since the year 1000 — with a sharp upward sweep of temperatures beginning in the mid-1900s.

This publication plunged Mann into the increasingly politicized debates about climate change. Over the past two decades, he said, that hockey stick has become more like a scythe: Research into historical climate data and a generation of continued warming has given it ”a longer handle and a sharper blade.”

In his speech Thursday, Mann argued forcefully against “climate doomers” who argue that onrushing climate change will unavoidably wreck human civilization.  

This perspective, he argues, only benefits polluters by depressing activism.

But Mann argued that humans were tiptoeing on the edge of an atmospheirc tipping point of our own making. 

“My themes here are urgency and agency,” he said. “There is still time.”

A sense of tragedy hung over Mann’s speech. A graph on climate investigative outlook Grist shows that if the energy transition had begun in 2000 — as proposed by Democratic presidential popular vote winner Al Gore — then keeping warming to the U.N. agreed-upon climate target of 1.5 degrees Celsius would have been a “bunny slope to ski down.”

Now, Mann said, it’s a far more treacherous descent. “ExxonMobil and others have bought us a ticket on the black double diamonds,” he said, referring to the most challenging ski route.

The scientist argued that life has long worked to moderate the climate — and faced devastation when it has failed.

In the early eons of life on Earth, life released more greenhouse gases when the sun was 30 percent dimmer — warming the planet — only to cut its emissions as the sun warmed. 

“It almost sounds like a religious explanation, like some sentient being is tuning the knobs to keep our climate in bounds,” Mann said.

But that’s a misreading, he argued.

James Lovelock, the progenitor of this “Gaia hypothesis,” was “frustrated” by these quasi-spiritual accounts. To explain how life could act to protect itself from the ravages of an often inhospitable planet, Lovelock used the analogy of a simplified world full of only white daisies.

In that world, the hotter it gets, the more the daises grow — and the more their spreading surface reflects light into space, cooling the planet without any conscious intervention.

“The system acts to keep the planet habitable for life,” Mann said. “Life itself participates in a way that keeps the planet habitable.”

“But there is a cautionary tale here,” Mann said. “At some point you hit a limit.”

At a certain point in the simplified ecosystem of Daisy World, the sun gets hot enough to kill off the daisies — the reflection vanishes, and heat suddenly increases rapidly.

In other words, Mann said, life can be pushed to a point — but the whole system can collapse past that point.

In at least one case — the Great Dying of 252 million years ago, in which 96 percent of all life died off — this collapse was driven by an onslaught of greenhouse gases: huge releases of carbon dioxide from volcanoes, sulfides from the deep seas and methane.

Mann emphasized that this isn’t an analogy or prophecy. He said that “climate doomers” — who argue that our current conditions already match the Late Permian period when that extinction got underway — overstate the case. 

“The truth is bad enough,” he said. “There’s no [current] evidence of runaway warming.” 

But in that extinction and others, Mann depicted a clear connection between atmospheric gases and mass extinction.

For example, the Chicxulub meteor that is infamous for killing off the dinosaurs didn’t actually do so, Mann noted: It was the global cooling from the dust cast into orbit by the impact.

The nearest analog to our current situation is a rapid warming spike that preceded the “hothouse Earth” of 55 million years ago.

Mann noted that’s rapid in geological terms — “tens of thousands of years, not tens of years, which is what we’re doing today.”  

Surviving life grew very small in this period — including the first tiny primates.

But that’s not a sign of resilience, Mann argued. Life became small because the large life died off.

“So when people say, ‘Oh, well, we’ll just adapt to warming.’ Yeah, we can adapt if we do nothing and warm the planet.”

But in that scenario, he said, “a lot of people are going to die.”

In one key area, climate scientists might have missed the mark.

They have correctly predicted the levels of warming we are currently experiencing for decades, Mann said. The climate “ is warming exactly as much as ExxonMobil predicted back in 1982,” he said.

But key tipping points — the weakening of key Atlantic currents, the rotting of Greenland and Antarctic ice sheets — are looming “sooner than expected.”

“Uncertainty is not our friend,” he said.

But since that 1.5 degree Celsius goal was set when the Paris Agreement was signed in 2015, commitments by world governments have cut projected warming from about 4 degrees Celsius to about 3 degrees.

Updated at 7 p.m. Sept. 8

Tags Al Gore Climate change global warming Michael Mann