Climate scientists have a heavier responsibility to get it right than most scientists, because what’s at stake may be almost everything we care about. Getting even the minor details right is hard and important. Getting the Big Picture right is immensely complicated and critically important.
American-born professor Will Steffen, who died in Australia last week, was a Big Picture guy. Based mostly at the Australian National University in Canberra but in contact with scientists around the world, he worked on the biggest picture of all: where is the climate system taking us?
Steffen’s greatest skill was bringing other scientists together in that enterprise. The informal, gradually expanding group that he and a few colleagues created has given us the concept of ‘planetary boundaries’ and identified the ‘tipping points’ that may overwhelm our efforts to limit the amount of CO2 in the atmosphere.
What has continuously preoccupied that group for the past twenty years was the fact that the mainstream predictions of warming showed a very smooth and steady rise in the average global temperature, driven almost entirely by human emissions of greenhouse gases. Not good, but at least no surprises.
Whereas the dissenters, drawn from a wide variety of disciplines, suspected that the Earth System’s response to the warming would be much more complex.
“I had eight years working with the best ecologists around the planet, and quite often we’re talking about abrupt shifts in ecosystems,” Will Steffen told me last year. “If the Amazon rainforest shifted due to a combination of heat and drought, it wouldn’t be a smooth process. It would be droughts, fires, a lot of CO2 emitted, and then a slow rebuild of a new ecosystem.
“That was true for the boreal forest as well. And we were talking about marine biology, which again appeared to show abrupt shifts in the past. I was also working with some people who studied ice sheets, and they were saying that some of the ice sheets, like West Antarctica, could melt quite abruptly.
“So it got me interested in this whole idea of tipping points in the Earth System and how they might affect the trajectory of the climate. It was a hard go to get these accepted by the physical climate people, but they were missing some important stuff.”
All the ‘founder members’ – Will Steffen, Johan Rockström, Katherine Richardson, Tim Lenton, Hans Schellnhuber, Jim Hansen, Paul Crutzen and 22 others – were involved in writing the influential 2009 paper “Planetary Boundaries: Exploring the Safe Operating Space for Humanity’.
That paper broached the notion of specific thresholds in the Earth System that might trigger abrupt and radical climate change if crossed. The authors stayed in touch, examining the horrifying implications of potential abrupt upward lurches in the global temperature, and by 2016 they were working on an even more alarming report. Tim Lenton explains:
“It was a fairly sizable group of us that have been friends and collaborators for more than a decade now. We’d been researching the possibility of different tipping points in the Earth’s climate system, and it was natural that we would ask: ‘Is there a global tipping point? Is there an instability of the whole climate?’
“You know, we burn a certain amount of fossil fuel, warm the planet up a certain amount, but then the feedbacks within the climate system start to amplify that to a degree that the climate change becomes almost self-propelling, because carbon is being released from degraded ecosystems, permafrost and so on.
“We’re not alone in being concerned about that, but we came together to raise a flag: that this is a risk that can’t be ruled out. And if it’s a risk that can’t be ruled out, then let’s have a go at trying to work out how big a risk it is.”
The group’s 2018 paper, ‘Trajectories of the Earth System in the Anthropocene’, nailed the new perspective down at all four corner. ‘Tipping points’ are now widely identified as the most dangerous aspect of the warming problem. That’s deeply discouraging, because we still don’t know exactly where they all are – but far better to know about them than not.
Today, our ‘never-exceed’ warming limits (an ‘aspirational’ target of never more than 1.5° Celsius and a hard target of never more than 2.0° C) are generally justified on the grounds that they are thought not to cross any of the tipping points. What was once heresy is now doctrine.
There remains a mountain of work to be done, but the climate perspective has shifted in the right direction. As Katherine Richardson said, “It’s this transition from local empirical data to studying global climate interactions that is the real crux. It can make you feel a little bit schizophrenic.” But Will Steffen did more than his share to enable the transition.
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