The ice-age U-turn that set the stage for the climate debate

Steve Schneider (left), Jim Hansen (centre), and S. Ichtiaque Rasool (right) at NASA Goddard Institute for Space Studies in New York, circa 1971. Image copyright: Stephen H. Schneider

On 13 July 1971, world-leading researchers gathered in Stockholm, Sweden, concluded their presentations about human influence on climate, and opened the meeting to questions from the press. But rather than asking about the most important climate meeting yet, the assembled reporters first looked to the meeting’s 26-year old secretary. “Where is Dr. Schneider? When is the ice age coming?” they asked.

The journalists sought out Stephen Schneider about a paper by him and his NASA Goddard Institute for Space Studies (GISS) boss, S. Ichtiaque Rasool, published just four days before. Using early computer models, they warned of a scenario where enough dusty aerosol pollution could be ‘sufficient to trigger an ice age’. For Steve, this would be the first encounter of many with the media’s interest in climate, leading him ultimately to help define how scientists influence the wider world.

As a PhD student at Columbia University in New York in the late 1960s, Steve came into contact with some of the world’s leading experts on climate. Wally Broecker, who at that time was helping establish the timing of the ice ages, lectured him on oceanography. A talk by Joe Smagorinsky from the US National Oceanic and Atmospheric Administration (NOAA), who was establishing some of the first computer climate models with Suki Manabe, played on Steve’s childhood fascination with hurricanes. And when he took a seminar by Ichtiaque talking about planets’ atmospheres – why Mars was too cold, Venus too hot, and Earth just right – he was hooked.

While writing up his PhD thesis he got a part-time job with Ichtiaque, tackling a key question at the time. Burning fossil fuels creates two types of pollution that influence climate – warming CO2 and cooling aerosols. But which one would win out? On the advice of fellow GISS scientist Jim Hansen, Steve used a method partly developed by astronomer Carl Sagan to calculate the aerosol effect. He put this into a model of warming from CO2 Ichtiaque gave him. They found that doubling CO2 levels in the air would raise temperatures by about 0.7°C – much lower than Suki’s earlier estimate of 2°C for this ‘climate sensitivity’ figure. But models where aerosols were spread everywhere experienced 3-5°C cooling, prompting Ichtiaque to write the ice age comment, referring to other controversial research of the time.

Ichtiaque had asked Steve to handle criticism of the study, but in the meantime Steve had managed to get an invite to the Stockholm gathering of leading climate scientists. Being a ‘rapporteur’ he was supposed to only be taking notes at the three week Study of Man’s Impact on Climate (SMIC) meeting, organised by Bert Bolin. But Steve couldn’t resist showing Suki some of his modelling work on clouds’ role in climate – and then the aerosol study was published. Ichtiaque had mischievously told a reporter that Steve was presenting the work at SMIC, forcing his young colleague to give a brief seminar, and face the press.

What should science do?

Steve at NCAR in 1974, where he’d started rising quickly through the ranks. Image copyright: NCAR

When he got back to New York, Steve had to go out and answer the many angry invitations Ichtiaque had received to defend their ‘irresponsible’ findings. But at the US National Center for Atmospheric Research in Boulder, Colorado, they were not angry – instead they invited Steve to come and work with them. If he hadn’t been tempted to take the job already, Steve was more convinced after his talk at NCAR. Whilst sat in his host’s office a call came through to tell Steve he had been fired. The head of GISS was unhappy that Steve had sent a letter to the New York Times responding to climate science critics without clearing it with him first.

By 1973, Steve was deputy director of the climate project at NCAR, and had started to think about whether models needed to be complicated to make reliable projections. General circulation models (GCMs) aimed for the most detailed simulations, but the computers of the time struggled to run them. Simpler models, perhaps using a narrow strip reaching into the air instead of the whole atmosphere, were easier to run – but how credible were they? Steve argued that credibility would take a ‘hierarchy of models’, for example simple ones to identify effects, and more inclusive ones to explore their full impact. That process might make the most of models Steve compared to ‘dirty crystal balls’. “The tough choice is how long we clean the glass before we act on what we can make out inside,” he said. In the 1970s, a rift emerged over whether models were useful at all. And similar questions – how credible models need to be before we act on their projections – still plague us.

Steve also got involved in a related argument over giving advice to politicians, in particular on whether supersonic air transport destroyed the Earth’s protective ozone layer. He was in a scientific panel that had to produce a report within two years, a timeframe Steve recalls fellow member Richard Lindzen calling ‘irresponsible’. “He claimed the science would not be definitive within that timeframe,” Steve later wrote. “According to him, whenever scientists are forced under political pressure to give answers that cannot be given, they are violating their scientific integrity. I totally disagreed, as did Mike MacCracken. MacCracken said ‘We are not arguing that we should tell people we know the answer. We have the best information there is, we should explain what we know, what the likelihoods are, and how much of this we can fathom. And we should say what research needs to be done.’ Lindzen stormed out of the meeting shortly thereafter.”

Conclusions based on evidence

One of Schneider’s closest NCAR colleagues was Starley Thompson, an early modeler of climate’s effects on ecosystems over long periods. Together they worked on what Steve called “simple simulation of complex models”. Image copyright: NCAR

That experience helped define Steve’s ‘risk assessment’ approach to scientific advice, particularly on climate change, but also brought surprise scientific benefits. Assessing the impact of supersonic aeroplanes needed a model with a stratosphere – something that had been missing from the 1971 study that had gained him so much attention. Adding it brought climate sensitivity up to 1.5°C, as CO2 in the stratosphere increases the amount of heat trapped nearer the Earth’s surface. The fact this heat never makes it through to higher altitudes causes cooling there, which is one of the main ways we know modern warming is caused by humans.

Meanwhile, measurements had shown that aerosol pollution isn’t actually spread out evenly across the world, though CO2 effectively is. This convinced Steve that his and Ichtiaque’s earlier results were definitely wrong. In a lecture he emphasised that humans were likely changing the climate through pollution, but it was unclear if cooling or warming would dominate. Fittingly, considering he was stepping back to an earlier position, he reversed a famous quote credited to Mark Twain to make his point. “Nowadays everybody is doing something about the weather, but nobody is talking about it,” he said. And once again, courtesy of a reporter who’d been in the audience, the quip got Steve into the New York Times.

Driven by these realisations, Steve read through everyone else’s research on climate sensitivity. By 1975, he brought them together in a paper of his own, putting the ‘best guess’ figure as 1.5-3.5°C, and went from projecting cooling to warming. Though he was later attacked for this, Steve stood by his actions. “Imagine the doctor who makes a preliminary diagnosis before the blood test and X-rays are in, and then they are different from the preliminary diagnosis, but the doctor sticks with it to be politically consistent,” he wrote. “This is not what we do in science – and we’re not ever ashamed of getting the wrong answer for the right reason.” Over the following 35 years of Steve’s career, the evidence for human-driven warming would pile up ever higher. But the arguments over model credibility, climate scientists’ involvement in political processes, and when action is taken, continue even today.

• This is the first part of my profile of Steve Schneider. Now read part two.

Further reading:

This year I’ve already written about the following pivotal climate scientists who came before Steve Schneider, or were around at the same time: Svante Arrhenius, Milutin Milanković, Guy Callendar part I, Guy Callendar part II, Hans Suess, Willi Dansgaard, Dave Keeling part I, Dave Keeling part II, Wally Broecker part I, Wally Broecker part II, Bert Bolin part I, Bert Bolin part II, Suki Manabe part I, Suki Manabe part II

Most of the material for this blog entry came from Steve’s book, ‘Science as a Contact Sport’.

S. I. Rasool, S. H. Schneider (1971). Atmospheric Carbon Dioxide and Aerosols: Effects of Large Increases on Global Climate Science DOI: 10.1126/science.173.3992.138
Stephen H. Schneider, Robert E. Dickinson (1974). Climate modeling Reviews of Geophysics DOI: 10.1029/RG012i003p00447
Stephen H. Schneider (1975). On the Carbon Dioxide–Climate Confusion Journal of the Atmospheric Sciences DOI: 10.1175/1520-0469(1975)032

Spencer Weart’s book, ‘The Discovery of Global Warming’ has been the starting point for this series of blog posts on scientists who played leading roles in climate science.