Monday, December 7, 2009

My Position on Anthropogenic Global Warming

I am often asked by friends and relatives about my take on Anthropogenic Global Warming (AGW), because I am an atmospheric scientist presumably with more knowledge and expertise on the subject than the lay person. I am also often hesitant to respond, because my current position on AGW is complex, full of caveats, and a careful explanation of such typically requires more time and patience than is available to me or the inquisitor. Below, I lay out my thoughts on AGW with as full an explanation as I can, complete with all the caveats. It is lengthy, but the written word allows for perusal at the reader’s leisure. I hope you will bear with me.
My overall position is that I accept the consensus view of AGW: there is a preponderance of the evidence that humans are causing an increase in global tropospheric temperature instigated by the combustion of CO2-producing fossil fuels. Now, don’t stop reading. Here come the first couple of caveats that some mischievous AGW opponent may be inclined to leave off in favor of selective quote mining.

Caveat #1: While I have the background to understand the complex science behind the AGW argument, I have neither the time nor the interest in poring through the immense and growing mountain of literature required to personally evaluate both sides of the argument. Doing so would require me to dedicate most of my waking hours to the subject, and I’ve got better things to do, including science that I personally find more interesting, albeit perhaps not as pivotal to our future on this planet. I have complete confidence in the brilliant scientists on both sides of the AGW issue that do dedicate their life to the subject; I’ll let them hash it out. Likewise, I have complete confidence in the scientific process; that is, the better scientific argument will prevail. The main point is this: I accept the veracity of AGW not because I have personally weighed both sides of the argument in any rigorous way, but because I accept the scientific method. I treat AGW no different than any other scientific area in which I possess insufficient knowledge to make a determination of veracity even though I may have the expertise or capacity to fully understand the area given a sufficient investment of time. For those that do not have the expertise or capacity to understand AGW, taking a position other than consensus is certainly illogical, as it would be for any other scientific question.

Caveat #2: I reserve the right to change my position on AGW as additional data and information become available. AGW is not a theory in the sense of the Law of Thermodynamics or Newtonian Gravitation. From the peer-reviewed literature that I have read on AGW, there are good arguments to be made on both sides of the issue. I personally know several very well respected scientists on both sides of the issue. For example, Dr. Roger Pielke, Sr. was on the faculty in the Department of Atmospheric Sciences at Colorado State University while I was in graduate school (he’s now at the University of Colorado) and I maintain a professional relationship with him to this day. He is a brilliant scientist and my interactions with him indicate that his ethics are second to none. He is also a vocal anti-AGW advocate (see his website for more info: http://pielkeclimatesci.wordpress.com/) in that while he accepts human-induced warming, he believes there are other significant forcings besides CO2. All is not resolved. Unlike evolution by natural selection, where religious creationists attempt to create a controversy where there is none within the scientific community, there is a real scientific controversy about AGW. There are two scientifically valid but opposing views on AGW and each deserves to be considered. Importantly, the weighing of this evidence must be done by experts via the scientific method, and specifically not by the lay person or the expert in the public arena. At present, the overwhelming consensus is that AGW is real.

I want to be very clear how scientific consensus is established. First, it is not established by petitions. Ever. Neither is it established by vote.  I was never asked, for example, as a member of the American Geophysical Union (AGU) whether I supported the AGU position on global warming.  Voting has its issues and does not allow for scientific argument.    How about the IPCC consensus?  Just because the IPCC has voted and come to a consensus does not make it a scientific consensus. Anyone who has ever been on scientific panels knows the politics behind them. I can easily put together a panel to give me the answer I want simply by excluding those opposed in favor of those that support my ideas. NASA does this all the time. In fact, it’s not uncommon for a NASA panel to be dissolved and then later reestablished (with different members) until such time as the chosen answer is delivered by the panel. There are also inherently conflicts of interest with many panels. Is it appropriate for the panel chair to oversee a panel that has a direct impact on their research? NASA mission science definition teams strongly influence the language that goes into solicitations for future missions. Is it any surprise that the solicitations have language that emphasizes the panels’ expertise in instrumentation often at the expense of others? Is it any surprise that many of the scientists involved in active missions just so happen to also be the very same scientists that helped produce the mission announcement of opportunity? Consensus is established over time in a slow motion duel of ideas as presented in peer reviewed literature supplemented by gray literature (i.e., conference papers). There is no quantitative measure or yardstick by which one can declare that scientific consensus has been met; it simply emerges, reaching the point where it becomes self evident. I am familiar enough with the literature and those involved in climate research to state that there is an overwhelming consensus. It is not unanimous! There are dissenters—honest to goodness dissenters with real issues and questions that have yet to be resolved. At this time, I have to go with the majority of experts. I have no qualms about changing my position if the consensus view, based on evidence, changes. I presently accept the veracity of AGW but with the knowledge that this could be a false position.

I would now like to throw in a little bit of commentary that is not directed toward establishing the truth about AGW. The first bit concerns the climate signal and the second concerns policy.

There is much debate in the literature and especially in the public arena as to whether the global temperature is increasing. The incessant debate over whether the temperature is going up, down or sideways misses the mark completely. The question should be whether there is an anthropogenic signal on top of the natural climate signal. If we were naturally heading into an ice age, it would be good to know whether humans might be slowing the progression. If we are naturally heading into a very warm interglacial period, it would be good to know if humans are accelerating the process. AGW, if true, operates regardless of whether the natural climate is warming, cooling, or staying the same. Antagonists of AGW sometimes suggest that the atmosphere has actually cooled over the last decade or two, or that it has periodically cooled and warmed over the last couple of centuries. This is irrelevant. What they need to do is show that cooling or warming can be entirely explained by natural variations. In other words, if the climate has indeed cooled in the last decade or sometime over the last decade, that is not sufficient to dismiss AGW. AGW opponents need to show that anthropogenic forcing did not offset the cooling. Doing this places them in exactly the same pickle that the AGW supporters currently find themselves; having to demonstrate complete mastery and understanding of the natural climate cycle. Likewise, it is not sufficient for AGW supporters to simply show the “hockey stick” temperature graph indicating a rapid rise in temperatures coincident with the onset of the industrial revolution. What this camp needs to show is that the temperatures are higher than they otherwise would have been. In other words they need to demonstrate that the natural climate would not have produced such a trend.

So, it seems that both sides need to establish what the natural climate signal is in order to determine whether AGW is true or false. Or maybe not. While some employ various complex signal processing techniques in attempt to tease out the different climate signals, would it not also be sufficient to determine the impact of rising CO2 under a range of reasonable natural climate scenarios? If the AGW supports could show that the temperature forcing is positive regardless of what the natural climate is doing, that should be sufficient. Likewise, if the anti-AGW camp can show that the forcing from CO2 is unimportant under a range of natural climate scenarios, that would also be sufficient. This is where models can help.
Although I do not consider myself informed enough to make a personal determination of AGW, there are some aspects of the subject in which I am generally able to make an expert assessment. One such area is that related to climate models, subject to the caveat below:

Caveat #3: Although I am familiar with climate models, I have never applied these models to the study of Earth’s climate. I have used these models for the purposes of terrestrial weather prediction (note: weather, not climate) and in application to the climates of planets other than Earth. I can provide no expert opinion on the specific application of the models to Earth’s climate, but I do have sufficient knowledge to understand the numerics and general principles of modeling, which are more or less universal constants for application to any planetary atmosphere, including Earth.

Much has been made that the climate models have difficulty reproducing past climate trends. Whether this is true is arguable; models do very well in some areas and less well in others. Still, it may be mostly irrelevant. Consider, for example, the climate of Mars.
We know that the climate of Mars has changed, and is likely currently changing. More so than Earth, Mars undergoes large orbital excursions due to the lack of a large moon to stabilize the orbit. These excursions produce variations in the magnitude and distribution of solar irradiance over timescales of thousands to hundreds of thousands of years—the so-called Milankovitch climate cycles. At times, the Milankovitch cycles likely result in water ice becoming stable in the tropical latitudes, as opposed to the poles where it is currently found. Changes in global temperature may also vary with the changes in solar insolation and the accompanying perturbations in atmospheric mass (most of which is CO2). Beyond these climate cycles, we basically have almost no idea of what produces other climate cycles on Mars, nor do we have much detail on what previous climates were like. For Mars then, we have a trio of problems. Not only do we not know the previous climate states in any detail, we cannot possibly test the Mars climate models (essentially Earth climate models with physical constants and processes appropriately modified for Mars) to determine whether they accurately reproduce the climate variations, nor can we be confident that the models have the necessary physics to reproduce the natural, long-term climate signal, whatever that may be.

Despite what sometimes seems like overwhelming and insurmountable ignorance about the Mars climate, substantial progress has and continues to be made. We are very confident that global temperatures rise when the atmospheric dust load is increased. This is a robust finding, and is independent of the trajectory of the Mars climate. It matters not whether Mars is warming, cooling, or holding steady. Dust produces a net warming of the atmosphere. We know this not only from observations, but also from models. Even though the Mars climate models are completely incapable of reproducing the long-term climate variations of Mars (and since we do not have any meaningful detailed information on these previous climate states, we would have no way of knowing the accuracy of the models even if they could produce such variations), we can use the models to assess how the climate responds to dust loading. The models do not need to reproduce the climate trend to establish the magnitude of forcing. Instead, the models must simply reasonably reproduce the current climate state. The difference here is in reproducing the climate state rather than time derivative of the climate state. The phrase “reasonably reproduce” is actually a fairly loose requirement. In fact, a simple time-independent, 1-dimensional model of the atmosphere--one with no atmospheric motion or variation in time whatsoever—is all that is needed to understand the basic climate forcing of dust. Going to a full 3-D time dependent climate model simply provides more fidelity but does not change the underlying physics or outcome.

So it goes for Earth. The natural climate may be heading off on some trajectory: up, down, sideways. Even though the models may not be able to reproduce this trajectory, it is still possible to use the models to understand how processes will perturb the trajectory. To me, this is the real crux of the AGW issue. It is not whether the Earth will warm, cool, or stay the same. It is weather humans are producing a perturbation on the natural climate. Consensus findings indicate that there is a human perturbation.

Now I turn to policy. Policy decision is, unfortunately, often entangled in the science of AGW. Whatever policy is enacted (or not) to deal with AGW has absolutely no bearing whatsoever on the veracity of AGW. If the consensus view of AGW is correct, than it is theoretically possible that policy could remediate (although not eliminate) the impact. If the consensus view is incorrect, than any implemented policy might theoretically be a costly folly. Enough of the theoretical, how about reality?

I have yet to see a credible proposal that will reduce CO2 emissions to inconsequential levels. Simply curbing the growth of CO2 emissions is not sufficient. The majority of the world has yet to industrialize, and it does, it will likely do so on fossil fuels. Reducing emissions from the industrialized countries may temporarily reduce the problem, but it will not solve it. There are billions of people in the rest of the world ready to take our place as oil, gas and coal consumers.

Further, is the increase of CO2 emissions sustainable? Can we continue on our pace toward doubling CO2 levels? Those who subscribe to the concept of peak oil may have something to say about this. Eventually, they say, the world supply of fossil fuels will run out, perhaps within the century. This will necessarily result in a reduction of emissions.
Associated with policy to counter AGW is the inherent assumption that a warmer climate is bad. There are obvious impacts if AGW is true: rising sea levels or perhaps the increase in prevalence and coverage of tropical disease, for example. On the other hand, large regions of frozen, agriculturally poor land might become arable. The opening of an arctic Northwest Passage could speed commerce and reduce the cost of products that advance the human condition. It is not my intention to argue one way or the other on this, but simply to point it out. If we were naturally going into an ice age, would AGW be bad? Or more fundamentally, is it bad to perturb the natural climate in any way, up or down?

The tragedy is that with the focus on AGW and the connection to fossil fuels the issues that ought to be front and center with respect to policy is lost. First, even without AGW, fossil fuels are dirty. Combustion of these fuels results in pollution that has been definitively linked to respiratory illnesses, acid rain, heavy metal poisoning of waterways, and the production of carcinogenic compounds. The drilling, extraction, transport and refining of oil is a dirty business with noticeable first order impacts that should be avoided. We should be reducing our reliance on carbon, and in doing so our emissions would automatically fall.
Another issue related to fossil fuels is that the money finances some of the most vile dictatorial and dangerous regimes around the world. It is in the best interest of those who believe in basic human rights to reduce and eventually eliminate world dependence on oil. Instead of spending trillions of dollars on wars in the Middle East, that money could have been put to better use funding alternative energy. Without petrodollars, terrorists would be hurling rocks from donkeys instead of training and coordinating overseas attacks on civilians. Iraq was funded by oil. Iran is funded by oil. The Saudis are funded by oil. Indonesia is funded by oil. Without oil, these nations are nothing but impotent.

In short, regardless of the veracity of AGW, we should be limiting our CO2 emissions. If AGW is false it is not a reason to continue our destructive ways. The AGW argument is not needed, yet it has become the focus on whether or not to reduce our dependence on fossil fuels. That is a shame.