In a short book titled What We Know About Climate Change, Massachusetts Institute of Technology meteorologist Kerry Emanuel explains why he believes humans are causing a global warming crisis. The book is really more of a short essay, approximately 10,000 words long with only seven endnotes. A significant chunk of the 10,000 words drifts away from the scientific discussion and addresses politics, messaging, and prescribed solutions.
The apparent goal of Emanuel’s book is to convince readers with minimal climate science knowledge that humans are causing a global warming crisis. The book, however, fails on several counts.
An Unstable Planet?
In Chapter 1, The Myth of Natural Stability, Emanuel argues the Earth’s climate is inherently fragile and susceptible to wild swings at the slightest human-induced perturbation. He mentions rapid polar ice cap advances and retreats as evidence of such climate fragility. Arguing that any human impact on the natural climate system is likely to send the planet’s climate out of control, Emanuel glosses over the fact that full-blown ice age epochs have dominated the past 3 million years of the Earth’s climate history.
As Emanuel acknowledges in his book, the occasional interglacial warming periods during the past 3 million years have typically lasted a mere 10,000 years or so (see http://en.wikipedia.org/wiki/File:Vostok_420ky_4curves_insolation.jpg). Our current interglacial warm period is 10,000 years old. Is altering the natural climate balance such a bad thing when we are soon likely to enter another 100,000 years of “natural” polar ice sheet advances?
Chapter 2 is a very short—less than 1,000 words—discussion of greenhouse physics. Emanuel explains the basic physics of how the Earth’s atmosphere retains heat. The chapter is not inherently controversial, but it is typical of how global warming activists often set up an unjustified logical jump. The author describes how the Earth’s atmosphere retains heat, and then makes the unsupported logical jump that any human-induced alteration of the amount of trace elements in the Earth’s atmosphere must be catastrophic.
Missing Positive Feedbacks
In Chapter 3, Why the Climate Problem Is Difficult, Emanuel acknowledges a substantial increase in carbon dioxide emissions will not by itself raise global temperatures very much. “Doubling the concentration of CO2 would raise the average surface temperature by about 1.9°F, enough to detect but probably not enough to cause serious problems.” For context, atmospheric carbon dioxide concentrations have risen less than 50 percent since the dawn of the Industrial Revolution.
Emanuel admits the two factors most responsible for future warming in alarmist computer models, water vapor and clouds, are subject to substantial scientific uncertainty. He notes projections of substantial future warming are dependent on the assumption that increases in carbon dioxide emissions will cause substantial increases in heat-trapping atmospheric water vapor and changes in cloud cover. These indirect impacts on atmospheric water vapor and cloud cover serve as a “positive feedback” in alarmist computer models, greatly enhancing the minimal warming directly caused by rising atmospheric carbon dioxide concentrations.
Emanuel unwittingly undercuts his own assumptions about substantial future warming when he acknowledges, “Calculations based on a large variety of computer models and observations of the atmosphere all show that as climate changes, relative humidity remains approximately constant.” Real-world observations, however, conclusively show relative humidity has not remained constant. Instead, as atmospheric carbon dioxide concentrations have risen and temperatures have gradually risen, atmospheric relative humidity has steadily declined (see Figure 5, atmospheric relative humidity as measured by the National Oceanic and Atmospheric Administration: http://clivebest.com/blog/?p=4730). As a result, a very important assumed indirect positive feedback of rising atmospheric carbon dioxide concentrations—relative humidity keeping pace with the modest temperature increases directly attributable to rising carbon dioxide concentrations—is not occurring in the real world. Without this very important assumed positive feedback, global temperatures continue to warm at a pace Emanuel admits is “probably not enough to cause serious problems.”
Wrapping up the chapter, Emanuel attempts to minimize the significance of the ongoing pause in global warming. Acknowledging there has been a “lack of appreciable global warming over the first decade of the current millennium,” Emanuel claims random and chaotic “climate noise” can alter the trajectory of long-term warming on scales of 30 years or more.
Emanuel’s climate noise theory has supporters and detractors, but it does little to support predictions of substantial future warming even if climate noise is currently weakening the Earth’s short-term temperature signal. Logically, climate noise would cut both ways, such that the 0.3°C rise in global temperatures from the late 1970s through the end of the last century appears to reflect climate noise sending too much of a false warming signal. If we accept Emanuel’s climate noise theory at face value and examine the warming trend from the late 1970s through the present, the Earth is on pace for approximately 1°C warming over the next century (see http://www.drroyspencer.com/latest-global-temperatures/). Once again, as Emanuel admits, this is “probably not enough to cause serious problems.
Applying Emanuel’s climate noise theory to a longer time period, the long-term pace of global warming appears even slower, as global temperatures actually cooled between the 1940s and the 1970s.
Problems with Climate Models
In Chapter 4, Determining Humanity’s Influence, Emanuel favorably cites global warming activist Michael Mann’s discredited “hockey stick” reconstruction of past temperatures to assert human emissions of carbon dioxide are the primary cause of recent warming. Even while citing Mann’s discredited work, however, Emanuel admits the types of proxy data Mann used to create his temperature record are “imperfect” and “have large margins of error.” As scientists have noted, proxies like those presented by Mann are subject to mischief and cherry-picking (see http://www.uoguelph.ca/~rmckitri/research/WegmanReport.pdf).
Emanuel points out there are a great many factors that must be incorporated into computer models. Moreover, as Emanuel admits, even small errors regarding some of these facts can cause large discrepancies between projected climate and real-world climate. Emanuel explains the challenges in creating accurate computer models:
“A typical climate model consists of millions of lines of computer instructions designed to simulate an enormous range of physical phenomena, including the flow of the atmosphere and oceans; condensation and precipitation of water inside clouds; the transport of heat, water, and atmospheric constituents by turbulent convection currents; the transfer of solar and terrestrial radiation through the atmosphere, including its partial absorption and reflection by the surface, clouds, and the atmosphere itself; and vast numbers of other processes.”
Emanuel acknowledges scientists know little about some of these processes, and even the ones scientists do understand often occur on a micro level too small for computer simulation:
“The representation of these important but unresolved processes is an art form known by the awful term parameterization.… A typical climate model has many tunable parameters that one might think of as knobs on a large, highly complicated machine. This is one of the many reasons that such models provide only approximations to reality. Changing the values of the parameters or the way the various processes are parameterized can change not only the climate simulated by the model, but also the sensitivity of the model’s climate to, say, greenhouse-gas increases.”
Deference to Models
Even so, Emanuel argues skeptics should defer to such inherently unreliable models:
“While it is easy to stand on the sidelines and take shots at these models, they represent science’s best effort to project the earth’s climate over the next century or so. At the same time, the large range of possible outcomes is an objective quantification of the uncertainty that remains in this enterprise. Still, those who proclaim that the models are wrong or useless usually are taking advantage of science’s imperfections to promote their own prejudices.” However, even if people point out the models’ shortcomings to advance their own views, this doesn’t change the fact—a fact that Emanuel admits throughout the chapter—that the models have serious shortcomings that render them unreliable.
The shortcomings of computer models predicting substantial future warming are illustrated by their failure to replicate recent climate conditions. The computer models that predict substantial future warming have consistently predicted more recent warming than has occurred in the real world (see http://www.see.ed.ac.uk/~shs/Climate%20change/Climate%20model%20results/over%20estimate.pdf and http://opinion.financialpost.com/2013/09/16/ipcc-models-getting-mushy/). Even United Nations Intergovernmental Panel on Climate Change (IPCC) lead authors say they will likely have to adjust the models to make them less sensitive to increases in atmospheric carbon dioxide (see http://www.spiegel.de/international/world/interview-hans-von-storch-on-problems-with-climate-change-models-a-906721.html).
In Chapter 5, Emanuel speculates about The Consequences he believes will occur from substantial future warming. Emanuel’s speculated consequences, however, derive from unrealistic assumptions about rapid future warming. “Projections based on climate models suggest that the globe will continue to warm another 3-7°F over the next century,” Emanuel writes. In reality, the IPCC projects approximately 2°C (3°-4°F) warming during the next century. This is at the bottom of Emanuel’s range of assumed warming.
Additionally, the IPCC predictions are themselves likely on the aggressive side, as real-world temperatures are warming at a slower pace than the IPCC predictions. Notably, IPCC has consistently been forced to dial back its predictions as it routinely overestimates future warming (see http://online.wsj.com/article/SB10001424127887324549004579067532485712464.html).
Emanuel’s assumed consequences of global warming are as devoid of evidentiary support as are his temperature assumptions. He attempts, for example, to link global warming to an increase in droughts, hurricanes, and crop failures. He provides no evidentiary support for such asserted links, and for good reason. In the real world, droughts are becoming less frequent and less severe (see http://onlinelibrary.wiley.com/doi/10.1029/2006GL025711/abstract and http://www.ncdc.noaa.gov/paleo/drought/drght_data.html), hurricanes are becoming less frequent and less severe (see http://www.forbes.com/sites/jamestaylor/2013/08/29/global-warmists-might-explain-why-no-hurricanes-midway-through-2013-season/), and crop production consistently sets new records as the planet modestly warms (see http://www.forbes.com/sites/jamestaylor/2013/01/16/fortified-by-global-warming-crop-production-keeps-breaking-records/).
Emanuel attempts to cover for his lack of evidentiary support by citing speculative ignorance. “Little-understood or unanticipated positive feedbacks might make matters worse than we expect,” writes Emanuel. “We are humbled by a sense of ignorance.” Yet there is no need for ignorance regarding the beneficial real-world impacts of warming on droughts, hurricanes, and crop production. The evidence is clear and well-documented. Assertions that all of this may for some unexplained reason turn for the worse in the near future represent fear-induced speculation totally divorced from the strong weight of scientific evidence.
Irrelevant Social Prescriptions
Chapters 6 through 8 devolve into social issues—Communicating the Science, Our Options, and The Politics Surrounding Global Climate Change. Emanuel’s prescriptions in each of these chapters are as unremarkable—except for their lack of supporting evidence—as are his assessments of the science in chapters 1 through 5. Given their lack of scientific support, his proposed social solutions are undeserving of time and attention.
In summary, Kerry Emanuel’s What We Know About Climate Change is a worthwhile read if you want to learn how prominent global warming activists view the issue at a very basic level. If you are instead looking for a discussion supported by scientific evidence, Emanuel’s book will leave you highly unsatisfied.
James M. Taylor ([email protected]) is managing editor of Environment & Climate News.