A book published in 2005 by the National Academy Press by John D. Cox entitled “Climate Crash: Abrupt Climate Change and What It Means for Our Future (2005)”? raises a critically important issue regarding the ability of global climate models to skillfully predict regional and even the globally averaged climate in the coming decades. (See also “Climate Prediction as an Initial Value Problem“)
The book is an excellent source on this subject. This weblog highlights this important contribution, but also there is a very important conclusion that the author missed.
First, the positive points.
A few quotes from his book are very insightful,
“On top of this new view of a more changeable climate is the unnerving discovery that it is basically unpredictable.” (page 3)
“Abrupt change means that, like the weather itself, climate sometimes behaves in ways that defy prediction. Processes in the atmosphere, in the ocean, and on the land are known to interact with one another, and even though scientists think they know all of the parts and all of the important processes, still they cannot be sure of the outcome of these interactions from one time to the next.” (page 146)
“A problem that Alley and other paleoclimate scientists refer to as the “insensitivity of models” or the “model-data gap” sounds like a technical issue but really is more fundamental. It means that the models are unable to reproduce accurately the numerous episodes of abrupt change that show up clearly in many environmental archives around the world. The reasons for this failure are not yet known, but the implications are plain enough. Until these highly sophisticated numerical representations of Earth’s climate system—running on the world’s most powerful computers—are able to get the past right, what reason is there to believe they can get the future right?’ (page 183).
“In 1997, Wally Broecker wrote in GSA Today that he had been “humbled”? by his lifetime study of Earth’s climate, a circumstance that may have surprised a few graduate students at Columbia University. “I’m convinced that we have greatly underestimated the complexity of this system,” he wrote. “The importance of obscure phenomena, ranging from those that control the size of raindrops to those that control the amount of water pouring into the deep sea from the shelves of the Antarctic continent, makes reliable modeling very difficult, if not impossible. If we’re going to predict the future, we have to achieve a much greater understanding of these small-scale processes that together generate large-scale effects.” (page 189)
“Not only are policy makers presented with what are likely to be overly optimistic expectations of the future, they are presented a profile with contours that look nothing like the record of climates past. The changes of the past are single lines or narrow bands that represent real data, whereas the projections of the future prepared for policy makers are large smoothed curves that represent the average results of many computer model simulations and a wide range of possibilities. “This tendency of the policy maker to see a smooth curve has to be really disturbing,” said Alley. “Because whatever it’s going to do, if it’s smooth, we’re going to be really surprised. It’s going to stagger, it’s going to jump. What happens regionally is not going to happen globally. And we really, I think, need to look at how variable it will be. What’s possible in the system, and where does it go”? (page 190)
And now the very important conclusion that the author missed.
It is the regional climate change that matters. The more homogeneous climate forcing of the anthropogenic well-mixed greenhouse gases, while clearly a concern, is not likely to pose as much of a threat to abrupt climate change, as the heterogeneous climate forcings. The book does make this point as given in the following text (but does not follow up on the implications of this issue),
“……..on the scale of human history. On this scale, of course, it is not the global but the regional climate changes that push humanity around. Hidden inside the variable of global temperatures is the more powerful circumstance of their differences between one place and another. Climate scientists know that changes in these temperature differences alter the circulation of the atmosphere, and this is where climate hits the pavement of human experience. This is what is most important to societies: not the temperature changes themselves, but how these changes affect precipitation patterns over time—where in the world it rains or snows and how little or how much.” (pages 164-165).
The book, however, does not adequately recognize the very important consequences of this paragraph. Since regional climate variability and change dominate society’s vulnerability to climate, the heterogeneous climate forcings of land use/land cover change, the diverse climate forcings of aerosol, and the biogeochemical effects of carbon dioxide clearly are of more concern as risks to abrupt climate change, than is argued by the author at the end of the book. As written, the author contradicts this perspective in the remainder of the book, and is using his view of the complexity of the climate system to make the very narrow point that “global warming” could result in a greater alteration of the Earth’s temperature than portrayed by the models, i.e.,
“In 2002, in a lecture to the AGU meeting in San Francisco, Alley reviewed the performance of the major climate models on which the Intergovernmental Panel on Climate Change has based its forecasts for a globally warming Earth. When it comes to simulating the past, across the board the models underestimate the changes that are known to have taken place. “On average, the models got two-thirds of what happened,”? he said. “It’s not a cold bias, it’s not a warm bias. It’s an insensitivity to changed boundary conditions … how sensitive the model is when you change things.”
“The least astonishing hypothesis that I get from this is that either the future warming projections are accurate or they have underestimated what we face in the future,”? he said. “There’s a lot of paleoclimate work to be done here to test this hypothesis,”? but if climate models are systematically underestimating reality, then the more radical-looking “high side” of temperature projections may be more accurate than the conservative-looking “low side” (page 189-190)
Climate, however, is more than temperature. A globally averaged temperature is an inadequate meric to represent other aspects of the climate system. This narrow conclusion presented in this otherwise excellent book contradicts its own thesis by limiting the discussion to global warming, and then to “temperature projections”, as if this were the most serious of the human disturbances of the climate system in the coming decades.
The real message to take from this book is that climate is a complex, nonlinear system in which skillful predictions of these transitions is a daunting, perhaps unachievable challenge. Since climate involves much more than the “temperature projections”, we need to identify what are the important climate variables that significantly affect society.
This is why we have promoted a vulnerability perspective as the more valuable paradigm to reduce society’s risk to climate change and variability of all types. To continue to pour many millions of research dollars into the very limited (and perhaps unachievable) goal of multi-decadal globally-averaged temperature forecasts is a poor use of these funds.
The last paragraph of the book moves in the direction of a vulnerability paradigm
“The news from Greenland, unfortunately, is that much more is possible in the climate system than anyone would have supposed. Changes can be big and fast and potentially dangerous to societies that are heavily invested in stability and resistant to adaptation. In the event of an abrupt change—a climate surprise—political arguments probably will no longer be about industrial emission controls, their fairness or economic viability. More urgent political and economic problems will command the attention of nations around the globe. In the event, it is in nature’s power to so change our world that even such basic questions as cause—whether the crash came naturally or not—could seem sadly beside the point.” (page 190).
However, the book does not take the obvious next step which is to specifically recommend that we move beyond the over simplistic approach of continuing to focus on a global average temperature, and of the radiative effect of increased carbon dioxide, as the dominant human climate forcing. As repeatedly reported on the Climate Science weblog, other human and natural climate forcings are much more significant in altering the climate. We need to develop a society that is resilient to whatever climate we face the future. A focus on reducing the emissions of carbon dioxide is, by itself, not going to reduce our risks.