January 2011 Archives
Roy Spencer is a professor at U. Alabama Huntsville and a former scientist at NASA. He has a strong background in meteorology and played a lead role at NASA in developing sensors on the Aqua satellite. When someone with this background makes a claim that CO2 doesn't cause warming, I'm inclined to take them seriously. Spencer's book, "The Great Global Warming Blunder: How Mother Nature Fooled the World's Top Climate Scientists" is at one level, a serious scientific argument in support of his hypothesis. On the other hand, the book is right wing populist attack on climate modelers, the IPCC, Al Gore, Jim Hansen, and indirectly, on Steve Martin.
Spencer's main scientific argument is that scientist have confused the cause and effect around clouds. He begins with a very readable presentation about thermal equilibrium and about the distinction between forcings of and feedbacks within the climate system. His main idea is that clouds can "force" global temperature. This is where I have my first issue with Spencer. Clouds are an inherent part of the climate system. Whether or not a cloud is formed (and what type of cloud is created) is a function of the amount of water vapor in the air and the temperature. If the ocean warms or the atmosphere cools, then the quantity and quality of the clouds will change. Of course, the change will then affect the temperature of the air or water, for example, by reflecting more radiation back into space. Forcings are things that are external to the system, for example, sulfur dioxide emitted by a volcano or radiation output by the sun. While I'm bothered by how he uses forcing and feedback, it doesn't affect his conclusion. His conclusion is essentially that natural oscillations in the climate system, for example the Pacific Decadal Oscillation, alter the amount of cloud cover, and that the cloud cover has a stronger influence on global temperatures than radiative forcing from CO2. He even presents a simple model that shows how everything works. He then shows that his model results agree with satellite data from NASA's Aqua satellite.
Sounds pretty great. Spencer spends a lot of time railing against the IPCC. Although many of his claims are bogus (more below), he seems to really hate the climate models. A major part of his argument is based on the assumption that simpler models must be better (he even appeals to Occam's razor). However, there are two major problems with Spencer's model. First, it's too simple. If processes like the PDO are really driving global temperatures, then don't we want a model that could represent the PDO? The PDO is a shift in the pattern of sea surface temperatures in the Pacific. Essentially, it's a pool of warm water and cold water sloshing around. Spencer's model can't actually produce a PDO (or an El Nino or an NAO) because his ocean is essentially a cup of water. I'm deliberately picking on his model, although I don't believe his conclusions rely on internally generated PDO-like cycles. More critically, he cherry-picked the parameters for his model. As a Murphy and Forester (2010) show, there are a wide range of parameters, all equally plausible, that cause his model to produce a weaker cloud effect (making CO2 forcing more important) yet still fit the satellite data. Skepticism is an important tool, but a good scientist applies it equally to his own work.
Spencer also rests much of his argument, or at least his dislike of the IPCC, on the supposed fact that the IPCC doesn't acknowledge that there is significant natural climate variability. This is absolutely, completely, 100% not true. By there very nature, the global climate models used by the IPCC have significant internal climate variability. My understanding is that all of the models have something like ENSOs, NAOs, and likely PDOs as well. Climate scientists look at the character of these patterns in their models and use them to determine whether their model is performing well. Furthermore, the IPCC models do a very good job capturing the global temperature pattern in the 20th C, which include any PDO-like effects. Finally, and more critically, Spencer completely dismisses all of the paleoclimate work in one fell sweep. The paleoclimate record is the only way of diagnosing the earth's climate sensitivity, since only by looking over thousands of years do we see CO2 changes comparable to what we're imposing on the earth now. Both the paleorecord and the IPCC models (which don't depend on the paleo-data) suggest that the earth's climate is highly sensitive to CO2. Good science requires multiple lines of evidence, and there are many independent data sets and models that indicate that burning fossil fuels warms the planet.
Now that we (or rather, Murphy and Forester) have taken down Spencer's main argument, I have a few other points to make about this book. The other main theme in Spencer's book is that the IPCC, climate modelers, Al Gore, and Jim Hansen are all elites who are deliberately ignoring the views of the average guy on the street. He repeatedly quotes recent surveys that say that the majority of Americans don't believe climate change is caused by humans as evidence that humans don't cause climate change. He also rails against the mainstream media's penchant for not highlighting scientific arguments against anthropogenic climate change. I would argue that the US media's tendency to give equal weight to all sides of an argument, no matter how marginal the views, inflates the importance of folks like Spencer and contributes to the majority of Americans doubting climate change. So, what about Steve Martin? At the end of his book, Spencer launches into a fantasy about what will happen when the world (meaning the IPCC and the like) wake up an realize that he is correct. This fantasy includes a movie, with Steve Martin playing the role of Spencer, since they have a "similar sense of humor." As a Steve Martin fan, I'm offended. Steve Martin is actually funny. Roy Spencer is just playing to a crowd.
Nick Record, signing off.
From Andy, just this brief correspondence:
Patagonia is awesome. We collected some temp profiles and are headed out to do more today. Saw sea lions, penguins, and the world's coolest cormorant.
And from Pete:
Meanwhile, here is the first taste.
The book should probably be titled "Sea level of my Grandchildren", as Jim Hansen's main argument, that bad things will happen if CO2 is kept above 350ppm for too long, rests heavily on his conclusion that higher CO2 concentrations would drastically raise se level. Hansen is one of the founding fathers of climate change science. He wrote a seminal paper on CO2 and global warming (Hansen et al. 1981) and famously testified to Congress in 1988. More recently, he became the target of one of the Bush administration's most publicized attempts to censor science. This book weaves back and forth between the science of climate change and climate change politics and policies. While he presents a view of how policymaking that few scientists get to see, I found his constant railing against special interests a bit tiresome, if not a tad naive. On the science front, Hansen fairs better, although I wish he would stop apologizing when explaining something technical.
The most interesting part of the book is how Hansen reaches the conclusion that 350 ppm is necessary to preserve society as we know it. He begins with a very readable presentation of CO2's role in the earth's energy balance. Essentially, CO2 reduces the ability of the planet to lose heat (received from the sun) through radiation. From basic physics, warm bodies are more efficient radiators (thanks Dr. Maxwell!), so the Earth's temperature must rise until the balance of incoming to outgoing radiation is restored. This argument is based on well-established physics, and the issue becomes how much of each gas is in the atmosphere and whether there are any feedbacks that could amplify or compensate for the warming. For example, does warming increase water vapor in the atmosphere, leading to more warming? Hansen does a good job presenting the uncertainty in these calculations, which lead to the basic conclusion that CO2 is the dominant factor determining global temperatures. Although calculations and simple models play a role, Hansen's most convincing evidence comes from the paleorecord. Ice cores from Greenland and Antarctica provide a long record of both CO2 levels (trapped in bubbles) and temperature (from oxygen isotopes). These records show a strong association between temperature and CO2. From this record, Hansen derives the earth's climate sensitivity, that is, the amount of temperature increase per unit of CO2 in the atmosphere.
Enter the grandchildren and their storms (or coastlines). As I mentioned, feedbacks in the climate system are key to establishing the amount of warming and the amount of change. Because ice and snow are white, they reflect incoming radiation at mostly short wavelengths that are not absorbed by the atmosphere. Thus, ice and snow tend to cool the earth. However, warming near the poles will reduce the amount of ice, exposing more ocean and land. Land will tend to reflect incoming radiation at longer wavelengths that can be absorbed by the atmosphere, leading to more warming. The ocean itself will tend to warm up, making it harder to create ice the next year. The warming ocean is central to Hansen's concerns about his grandkids. Warmer waters around Greenland and Antarctica will tend to accelerate the melting of the ice sheets, something that is already occuring. This adds water to the oceans and raises sea level. Hansen finds plenty of evidence in the paleorecord to support major changes in sea level associated with warming. He also notes that human societies developed in a period of unusually small changes in sea level. He concludes that CO2 levels above 350 ppm will lead to increases in sea level faster than humans have ever experienced.
After reading the book, my impression is that Hansen is a very smart, if slightly strange, cat. I think he makes a convincing case that climate change is happening, linked to CO2, and a significant threat to human societies. I've now started working through Spencer's "The Great Global Warming Blunder." Hopefully, I'll have something in a couple of weeks.
Late update. I just watched Hansen on the David Letterman Show. He was much less nerdy than I'd imagined from his book. Not that I'm in any position to comment on another's nerdiness.
Hansen, J., Johnson, D., Lacis, A., Lebedeff, S., Lee, P., Rind, D. and Russell, G. (1981) Climate impact of increasing atmospheric carbon dioxide. Science, 213, 957-966.