This is an excellent book. Roy Spencer is a climatologist, a Principal Research Scientist for the University of Alabama in Huntsville, the U.S. Science Team Leader for the Advanced Microwave Scanning Radiometer (AMSR-E) on NASA’s Aqua satellite, and he has served as senior scientist for climate studies at NASA’s Marshall Space Flight Center in Huntsville, Alabama. So he speaks as an expert in climate in this book. But the good news is that this book is fully accessible to the general reader. Spencer has not included details of the science. He stays at the level of principles and policy.
He gets at the crux of the problem with climate models: they assume a positive feedback loop that will drive the climate to extremes. He points out that there is nothing in the science to support this. His own intuition is that the climate system is robust and has negative feeback loops to keep it stable. Here's his argument in a nutshell:
The increase in water vapor expected with global warming has more confidence among climate modelers than any other change. The conventional wisdom is that the warming tendency at the Earth's surface caused by the extra carbon dioxide will result in faster evaporation of water, and thus a humidifying of the atmosphere. Since water vapor is the atmosphere's dominant greenhouse gas, this would in turn amplify the warming. All of the dozen or so major climate models that are used to predict global warming behave in this way.In short, the climate models used to set policy are fatally flawed. They don't include precipitation systems. Spencer expects this to be a negative feedback loop which will prevent runaway global warming. But the science hasn't been done. So the models don't handle this fact.
There are, however, a couple of reasons to question the strength of this amplification of the warming by water vapor.
First, the greenhouse effect due to water vapor is not controlled by the surface evaporation, but by precipitation systems. The amount of water vapor in the middle and upper troposphere -- the atmospheric layers that contribue most to the natural geenhouse effect -- is controlled by complex processes in precipitation systems. Even though surface evaporation tries to fill the atmosphere up with water vapor, precipitation does not allow that to happen. At typical evaporation rates, it would take onl a week or so for the atmosphere to approach saturation (100 percent relative humidity).
Instead, near-surface relative humidities average closer to 70 percent, and in the subtropical high pressure zones at an altitude of a couple of miles, relative humidities can be astonishingly dry: 5 percent or less. Preciptiation systems, in effect limit the natural greenhouse effect -- most likely, in proportion to how much sunlight is available.
Since the water vapor content of tghe atmosphere, and thus the natural greenhouse effect, are under the control of precipitation processes in clouds, we cannot really know how much the atmospheric water vapor content will rise with the CO2-induced warming tendency without also knowing how precipitation systems will change with warming in their efficiency at removing water vapor from the atmosphere.
And it just so happens that the controls on precipitation efficiency are probably the least understood of any atmospheric process. And that wich we do not understand, we tend to downplay in importance. We can't include a process in a climate model that we cannot quantify.
Elsewhere he talks a bit about why he expects precipitation systems to provide a negative feedback:
Since previous theoretical work has indicated that an increase in precipitation efficiency results in cooler climate with (somewhat counterintuitively) less precipitation, we know that the climate system has at least this one thermostatic control mechanism at its disposal -- if it chooses to use it. If such a mechanism is indeed in operation, the net effect of manmade greenhouse gases wouldn't even be able to measure it. A small increase in precipitation efficiency in response to the warming tendency from extra carbon dioxide would potentially result in no measurable change in either temperature or precipitation. Most of the changes will have occurred inside precipitation systems, where the mysteries of climate sensitivity are kept hidden from our weather sensors.Chapters in the book are dedicated to showing how various parties have inducements to oversell doomsday scenarios. Together these parties have created a mutual admiration society that reinforce each other:
The foregoing examples and arguments represent one possible climate stabilizing mechanism which I present as a hypothesis. It is not entirely original, as it buildsw upon the published work of others. While far from being proved, it is still consistent with much of our conceptual understanding of how the atmosphere operates. I would expect that there are other possible climate stabilization mechanisms as well which I have not considered here.
The overconfidence of some scientists, along with the underlying motives o9f environmentalists, politicians, and the media, is leading to some impatience with the views of global warming skeptics. As a result of the apparent nobility of their mission to spread the truth of imminent global warming catastrophe, some environmentalists and reporters have started to demonize those who would dare to disagree with them. At this writing, a Google search for the phrase "climate change denial" now returns over 70,000 web pages.Read this book is you want a skeptic's viewpoint. Spencer monitors the earth's temperature with his AMSR-E sensor. He knows what he is talking about. Monthly on his web he posts the temperature of the whole earth, the tropics, and each of the northern and southern hemispheres. He is not a crackpot. And I truly believe that in 20 years people will come to see him and the skeptics are the true scientists of this era. The many modelers will be discredited. (Read the book to understand how these scientists can be led astray!)
Calling someone a global warming denier implies that global warming skeptics do not believe in global warming. But this charge is completely false. I know of no skeptics who deny that global warming has happened. In this way, those whose agendas are so important to them that they cannot simply let the facts speak for themselves are no resorting to intimidation, under the guise of "good science."
Extreme statements like "all reputable scientists believe in global warming" are, at best, misleading. At worst, they are propaganda. The purpose of such statements is to cast ad hominem insults in an effort to discredit others with opposing viewpoints. If you don't agree with the majority of scientists, you are a crackpot, or a denier of the holocaust or the dangers of tobacco. This is a favorite techniuqe in the propagandists' bag of tricks.
One final word: read the book because it is fun. Spencer has a light touch and a sense of humour. He has written a book on a most serious subject but in a way that you can easily learn the essentials in a day and find yourself chuckling as you read his account. The book is insightful. It is authoritatitive. It should be read by everyone.