Is There a Climate Crystal Ball?
When it comes to what society should do about global warming, there is quite a lot to consider. While reducing emissions is the clear end-goal, the speed at which it’s done and how much of today’s time and money is spent on mitigation or adaptation depends on how much immediate danger climate change presents during our lifetimes, or those of the next generation. It’s the near future most people are concerned with — perhaps too concerned when “near future” is a synonym for “my electoral term in office” or “my spell as CEO.”
The overall effect of manmade greenhouse gases on the climate is modeled in different ways, but only one measure is considered “policy relevant.” It’s called Transient Climate Response (TCR), defined as the global mean-temperature change on the day that carbon dioxide (CO2)has doubled over pre-industrial levels, given a rate of increase of 1 percent per year. Climate scientists believe that Earth will reach a doubling of CO2 within the lifetime of a child born this year. If TCR is high, society must act very quickly, and the amount spent must be proportional to the immediacy of the danger. If TCR is low, then temperatures won’t go up much, in which case there is more time, and people can spend less money now.
It is often said that climate models are like crystal balls. Scientists can gaze into them, but due to the basic constraints of any modeling, the results are cloudy. Scientists know the basic physics of the atmosphere well enough to capture the big trends, but the smallest atmospheric features are still being fine-tuned. So unlike soothsayers and fortune-tellers, climate scientists don’t make bold pronouncements, but instead couch their projections in caveats and careful language to be honest about the uncertainty involved.
No such humility is found when one examines the claims of climate contrarians. To present themselves as reasonable, the professional demagogues do not deny that the climate is changing or that humans are changing it. Instead, they keep insisting that TCR is low, because a low TCR supports their primary arguments: The threat is small, there’s plenty of time; therefore current investment in mitigation should be equally small (or even nonexistent).
What evidence do they produce to support a low TCR? It’s the usual cherry-picking: A handful of studies of varying quality that propose a median TCR value of around 2.34 degrees Fahrenheit (1.3 degrees Celsius), while ignoring other recent studies that suggest higher values. Tellingly, those low-end studies all focus on the most recent decade, while the higher projections come from studies of the Earth’s history. So contrarians are relying on 10 years or so of data, and ignoring the results of studies of thousands of years of data.
Drowning in the furor, decision-makers, legislators and the public discourse become collateral damage. The debate will continue to rage for years to come, as both sides try to produce definitive arguments, papers, claims and counterclaims. The latest ammunition in this war of rhetorical attrition is a new (paywalled) paper published in the journal Nature Climate Change, “Inhomogeneous Forcing and Transient Climate Sensitivity,” by Drew Shindell, an expert in atmospheric chemistry at NASA.
Studying short-term climatic responses (TCR), Shindell found that a number of assumptions about the way the atmosphere responds may be skewing the models to underestimate climate sensitivity. So, in essence, this study is polishing the crystal ball, finding that previous TCR findings might be too low.
What is the significance of Shindell’s work?
“[Findings] suggest that climate sensitivity is most likely towards the higher end of its nominal range…achieving climate protection goals will most likely require emissions reductions towards the high end of present estimates” [author’s emphasis].
Who’s right? Nobody really knows. It’s a fiendishly complex subject: Important, hotly contested and appropriately contentious. The crystal balls of climate models are only as good as modellers’ understanding of the natural world. As more is learned, the picture becomes clearer. The fact is, the only way to find out for sure how sensitive the climate is would be to take measurements after the climate has completely changed. When humans stop pumping greenhouse gases into the atmosphere, that’s when it will be possible to know just how much immediate damage has been done. After that, society must wait a long time to find out how much more committed warming is due — damage locked into the system but not yet evident — as ice continues to melt, oceans rise and the climate adjusts.
In the meantime, how should civilization react? How much faith should be put in our hazy crystal ball? It seems that those arguing for inaction are promoting complacency based on a curious logical inconsistency. So far, studies have found that the temperature anomaly is between 1.4 and 1.6 F (0.8 and 0.9 C), to date, and that’s for an increase in CO2 over pre-industrial levels of around 42 percent — from 280 parts per million (ppm) to 400 ppm. It’s hard to understand how, if CO2 concentrations double to 560 ppm, that the temperature will go up only another 0.32 F (0.4 C), particularly when Earth’s losing albedo (the property of ice that reflects heat back into space), oceans are warming rapidly as a result, humidity is increasing and people are still cutting down forests and changing land use. A crystal ball is unnecessary to see that such an optimistic expectation is misguided.
There’s only one fact that emerges from all of this: Nobody really knows what’s going to happen in the future. It might not be as bad as most scientists think, but then again it could be worse. Assuming the best-case scenario isn’t necessarily prudent, especially when those advocating that humanity do little or nothing are so often aligned with the fossil fuel industry and other vested interests.
Society needs to respond in a prudent way, without overreacting or complacency — and could certainly do without the constant conflation of ideology and science in biased media and contrarian blogs. There may be great risk on the horizon, and humanity should respond appropriately. Either way, if civilization gets it wrong, it’s likely to break science’s crystal balls.
This is a repost of an article that first appeared in Livescience: Expert Voices