Climate Scientist Steve Schneider Passes
by Bill Chameides | July 20th, 2010
posted by Erica Rowell (Editor)
I sat down yesterday to start today’s post. It was to be on a paper that covered some topics I first learned about from Steve Schneider back in 1994. Just as I began, the news came in that Steve had died. What are the odds, I thought. But then I realized that it’s the unexpected, low-probability events that often get you.
Steve began his career as a climate scientist in the 1970s. Like many working in the climate field back then, Steve was unsure about the direction of the future climate — perhaps cooling from aerosols or warming from carbon dioxide (CO2). He wrote in a 1977 paper [pdf] in the journal Nature that “we just don’t know enough to choose definitely at this stage whether we are in for warming or cooling — or when.”
His view changed considerably as he learned more; by the late 1980s Steve had become one of the most passionate and committed (some might say outspoken) advocates for action on climate change. Because of Steve’s full-throttle engagement in the public policy debate, he was viewed with suspicion by “purists” in the scientific community. His election to the U.S. National Academy of Sciences in 2002, despite those purists’ reservations, is a testament to the strength of his science.
While I’d met Steve in passing at numerous meetings, my first opportunity to talk with him at length didn’t occur until 1994. It was at a workshop he organized at the Aspen Global Change Institute, the topic of which was “Anticipating Global Change Surprises.”
While most workshops focus on what we know, this workshop homed in on what we don’t know about the climate system. It made for a fascinating two weeks. While climate skeptics then (and now) like to point to uncertainties in our understanding of climate as a reason to delay action, our discussions in Aspen led us to the opposite conclusion. It was not what we knew but what we didn’t know — the potential for surprises — that was truly worrisome.
Two Notable Takeaways: Tipping Points and Expert Elicitation
I recall a focus on two concepts that at least for me back then were relatively new:
- Tipping points: sudden, irreversible shifts in the climate system that could result from the slow rise in greenhouse gases, causing potentially catastrophic effects;
- Expert elicitation: interviewing experts in the field and analyzing their responses to increase our understanding of complex systems like the climate.
The tipping points we discussed included: positive feedbacks with terrestrial carbon reservoirs, the release of methane clathrates, and ice-albedo effects.
In a recent interview, Steve said, “We know that there are probably hundreds of tipping points. We don’t know precisely where they are. Therefore you never know which ones you’re crossing when. All you know is that as you add warming, you cross more and more of them.”
With regard to expert elicitation, I remember Steve reporting the results of a study that queried climate scientists from both sides of the climate change debate and asked them something like: “What is the likelihood in your judgment that CO2 emissions will lead to serious climate disruption?” Even the most skeptical gave a non-zero probability; my recollection is that the smallest probability was about 10 percent — not that small, Steve pointed out, when you’re talking about taking chances with the planet.
New Paper Expands on Tipping Points and Elicitation
Which brings us to that paper. Just last week the Proceedings of the National Academy of Sciences published a paper focusing on those same two topics: tipping points and expert elicitation.
Author Kirsten Zickfeld, then of the University of Victoria, Canada, and co-authors (including the University of Calgary’s David Keith who had presented a paper on expert elicitation at the Aspen workshop back in ‘94) queried 14 climate scientists (including Steve) on how various levels of greenhouse gas climate forcing will affect climate. Some of the results:
- The greatest uncertainty in climate predictions arises from gaps in our understanding of clouds and their interactions with climate.
- The most likely tipping points the experts identified were: large losses of the Greenland and/or West Antarctic ice sheets, disruptions in the El Niño Southern Oscillation, a shutdown in the Atlantic Ocean meridional overturning circulation (also known as the conveyor belt), and a loss of terrestrial carbon.
Perhaps most significant and surprising were the high probabilities assigned by the experts for crossing these tipping points.
For example, when asked to consider a scenario that stabilizes CO2 at levels of 550 parts per million volume (100 ppmv larger than what the Copenhagen Accord proposes):
- all respondents rated the probability of crossing a tipping point at 20 percent or greater and
- eight at more than 50 percent.
The most ambitious scenario the study considered had CO2 peaking at about 450 ppm mid-century, then declining to pre-industrial levels by 2200. Even for this scenario, most of the experts rated the tipping-point probability between 10 and 20 percent. That seems uncomfortably large to me. We don’t know if it will definitely happen, in fact it is not all that likely, but I still don’t like the odds for an event with such serious repercussions.
Steve didn’t like the odds either. He felt passionately that we shouldn’t take chances with the planet — probabilities of catastrophe like those cited in the recent Zickfeld et al paper scared him and energized his drive to understand the climate and mitigate climate change, even while fighting off a potentially deadly cancer.
As I said earlier, it’s often what you don’t expect that gets you in the end. Fighting against the odds, Steve beat cancer and immeasurably advanced the cause of climate change. But he was surprised by death sitting in an airplane where the odds were in his favor. We are the sadder for it. We have reached an unanticipated tipping point — a world without Steve Schneider.filed under: carbon dioxide emissions, climate change, faculty, global warming
and: climate, climate science, expert elicitation, greenhouse gas emissions, Stephen Schneider, tipping points, U.S. National Academy of Sciences