Attribution: Blowing in the WInd
This is the fifth in a series on the attribution of climate change; that is, how do we determine to what extent the observed warming is caused by humans? The earlier entries are cataloged at the end. (This one should, perhaps be the first!)
First a return to basics: I received a good letter from a reader about the difficulty of determining trends and attribution from, primarily, the last 150 years of observations. The challenge seems even more daunting with the observational evidence from the distant past of a cycle between ice ages and temperate periods. One of the reasons that we can predict with confidence that the globe will warm is the large, observed increase in carbon dioxide. Carbon dioxide warms the planet; this has been known since about 1800. The warming comes from carbon dioxide holding infrared radiation, heat, near the surface of the Earth. The quantitative physical description of this process is simple and well known.
Carbon dioxide, therefore, is different than in the past. It is much larger. It can “force” the temperature to be warmer. (Old, yet relevant, blog) It is the fact that we have this carbon dioxide forcing that we can both make confident predictions and look for signals of attribution. I have been trying to think of a good metaphor to describe forcing, that also maintains some relevance to climate change. (Help?) Here is one that I pose. Imagine that you have a small bell hanging on a string from a beam on your porch. If there is wind, then it will blow the bell and it will ring. If there is more wind, then the bell will ring with different characteristics, perhaps louder, more frequently, more erratically. You could designate the wind as “forcing” the bell by blowing it around. Call this the “natural forcing.” If you were compelled to science you could keep a record of wind speed and direction (perhaps other variables) and a record of the characteristics of the bell ringing.
Now imagine that you keep a small mallet on the porch, and that you hit the bell. This is “anthropogenic forcing.” (Let’s see: human-caused, manmade, womanmade --- isn’t it interesting that manmade is a “word,” and “womanmade” is not?) Hitting the bell, a new type of forcing, will have a distinctly different sound. There will be a sharp sound, followed by a ringing of the bell’s body, and then, in the end, because the hit will cause the bell the swing on the string, it will sound much like it was blowing in the wind. There are a set of characteristics of the ringing from hitting the bell that are distinctly different than the ring from blowing in the wind.
It is the difference in the characteristics of the bell blowing in the wind (“natural”) and the bell hit by the mallet (“anthropogenic”) that allow the definition of a “fingerprint.” This fingerprint can be used to determine whether the bell has been hit – or not?
When we look at atmospheric observations and measure that it is warming up, we are faced with a far more complex problem than a bell dangling from the porch in the wind. Still, though, the basic ideas are the same. We have a known anthropogenic forcing agent, the carbon dioxide (plus others!), and we have a set of fingerprints. Examples of the fingerprints include greater surface heating at the North Pole than at middle latitudes and at the South Pole. The complexity and importance of the climate problem requires that we identify a thorough set of fingerprints. These include the spatial and temporal structure of changes at the Earth’s surface, changes in the vertical temperature structure of the atmosphere, changes in the vertical temperature structure of the ocean, changes in ecosystems, and the list goes on.
One path to attribution of warming to human activity is to identify enough characteristics of the fingerprint to make a convincing determination. Imagine that you generate a long list of attributes of the fingerprint of climate change and some you find in the observations and some you do not find. Because you find one does not prove human-caused climate change. Because you do NOT find one does NOT disprove human caused climate change. One is faced with the analysis of a complex, varying system and the determination of uncertainties.
The figure below from Ben Santer at Lawrence Livermore National Laboratory is a summary picture of the variables in which human-caused signals of climate change have been identified. This is from a lecture in my class in 2008, and the entire lecture is here.
Figure 1. Taken from class lecture by Ben Santer. This figure is a summary of geophysical parameters in which fingerprints of human-caused climate change have been found.
WU blogs on Attribution of Climate Change to Human Activities:
WU Blog on Models and Attribution
Updated: 4:36 PM GMT op 27 juni 2008
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A Summit on Climate Prediction
Climate Summit: What Direction Now?
I’ve been going to a lot of meetings lately where we are talking about where the climate modeling community is talking about what to do next? What comes after the IPCC Fourth Assessment Report (AR4) as the results of this assessment permeates society?
The World Modeling Summit for Climate Predictions: The first meeting I attended was hosted by the European Center for Medium-range Weather Forecasts and sponsored by the World Climate Research Program, the World Weather Research Program, and the International Geosphere-Biosphere Program. This meeting of more than 100 scientists had people from both the weather and climate community. Much of the discussion was, in fact, about the efficacy of starting climate prediction efforts that are in the spirit of weather forecasts. At the core of the discussion was a recent paper by Tim Palmer and co-authors on “Seamless Prediction,” the idea of looking at scales from regional to global weather forecasting, to monthly, to El Nino, to decadal, to century long forecasts in an integrated, consistent matter. This is a subject of significant controversy because the method, practice, and evaluation of model performance is quite different in the weather and climate communities.
While there is a still evolving message coming from this summit, it is safe to say that all agreed that a much more robust ability to predict climate on decadal scales is needed. This will be required to provide information that is good enough for resource managers to make decisions about, especially, water resources. Much of the discussion was whether or not we have to wait until we have global models capable of modeling, explicitly, cloud systems. These cloud-resolving models are many years and several generations of computers away. It is my opinion that we cannot “wait” for these models; we have the potential to provide much more robust information with current and next-generation models.
I am of the camp that we should focus on developing a generation of climate prediction models that are at comparable resolution to the current generation of weather forecast models; that is, approximately a 20 km grid size on the Earth’s surface. At this resolution we should be able to represent the mechanisms, low level jet streams, which supply moisture to the continents. We should also do a reasonable representation of topography, land-ocean contrast, as well as the representation of desert boundaries. With this capability, then we should be able to provide much more robust analysis of regional impacts of global warming.
Both of these paths are necessary, but the question of priority is a question of resources. Again, thinking about time scales is important. We will need information for policy, infrastructure expenditures, and adaptation in the next 2 years, 5 years, and 10 years. Scientific investigation can contribute to answering these questions. Therefore, a set of requirements for the scientific community arises from outside the scientific community. This can, and often does, stand in contrast to the requirements generated by scientists. Again, opinion, I believe our community must organize and allocate resources to address these questions as best as we can at any given time.
One of the truths of climate and weather prediction is the need for high-performance computing. Climate and weather modeling has, from its beginning, been one of the drivers of high-performance computing. The development of computational platforms is not straightforward and the underlying hardware has undergone great changes. Twenty years ago custom hardware was made for scientific computing. This business model was too costly, so today high-performance computers are based on commodity hardware, and it is much harder to program large codes, like climate models, on these computers. A new challenge that we are facing today is the fact that computer chips are coming up against physical limits of size and their ability to cool.
The links above give you access to all of the presentations from the Summit.
The other meetings I have attended include an excellent workshop on the numerical techniques for future climate models (see also, this discussion and on facebook?) and, right now, the annual meeting of the Community Climate System Model, where a model for the next IPCC assessment is being configured.
Are you interested in reports from these meetings?
Breaking Down the Problem
Problem Solving: Breaking it down
I’m taking a break from the attribution series to write about complex problem solving. This is in response to the post from the TimesOnline on the Copenhagen Consensus. Here is the primary link to the Copenhagen Consensus. This is an interesting list developed by the Copenhagen Business School. The Consensus Project is headed by Bjorn Lomborg , who has become a controversial figure in the community. The project aims to look at the great problems of the world taken together and in the face of both monetary resources and capabilities. Then it is determined which are the most urgent to address. In general, full-on attack of the climate change problem does not come out on the top of the list. (It seems that some of the readers of my Wunderground blog use this to dismiss the importance or correctness of climate change science.)
In my class at Michigan on climate-change problem solving, we developed the following framework for breaking down the climate-change problem and setting it in relation to other problems. There are three axes on this graph: temporal, spatial, and wealth. Sometimes, we have drawn the “wealth” axis as “ethics,” but, bluntly, “wealth” is more of a determinant in addressing the climate-change problem than ethics. The ethical aspects to addressing climate change are complex and sit in a different type of relationship.
Figure 1: A framework for breaking down the panoply of elements that make up the “climate-change problem.” The idea is to consider the near-term and the long-term, the regional and global aspects, and the relationship to wealth. Other important aspects of the problem are ethics, urgency, etc., but these carry a relationship different than time, geography, and wealth.
We then set down the major driving issues that arise when considering climate change. These are population, energy, consumption, and societal success (i.e. the economy). It is immediately apparent that the time scales that come from the consumption of energy, which impact the economy and societal success, are short. Here in the early 21st century, we work on very narrow margins. Because the consumption of energy is so tightly correlated to wealth, the protection or growth of wealth places a near-term urgency on energy, energy security, and economic growth. This urgency trumps the notion of sustainability; hence, climate change.
Where does climate change sit? Scientists maintain from a knowledge-based perspective that there is an urgency to address the climate change problem. This urgency is based on the notion that we must act now in order to have any hope of holding carbon dioxide levels low enough to prevent “dangerous” climate change. This near-term urgency of climate change stands in contrast to the long time it takes to realize benefit from any actions that we take today. Climate change, therefore, sits in an ambiguous relationship to these other problems of energy, energy security, consumption and economic success. In fact, climate change is a little bit like ethics, it permeates all of the possible decisions that could be made about these big-ticket items. Most directly, however, if climate change is considered in the here and now, then our sources of cheap energy are challenged, and we exist so near the margins, that increasing energy prices immediately threaten the economy, cause turmoil in the world, and climate change falls down the list of urgent considerations. The fact, that action today does not yield benefit for decades or centuries, becomes motivation to defer attention to the climate-change problem. We rely on figuring it out as we go along.
We live in a world where wealth and consumption rules. This leads us to market-based approaches to the climate-change problem. Ultimately, it is the market (euros, dollars, yen, yuan, and rupee) that is the unifying network of our species. It is the idea that we can represent the real cost of energy extraction and use and management of our energy waste that sits at the foundation of the most likely strategies to address, rationally, the problem of global warming. What is the evidence that we can face such a problem rationally?
This blog started with the idea of setting the climate-change problem in relation to other problems faced by society. I introduced the idea of trying to consider the near-term and the long-term, wealth, and locality to bring structure to the problems. From here, we can seek rationality and convergence towards solutions.
I will close with what are the definitions of near-term and long-term that we can manage rationally? Near-term is less than 10 years. Long-term is, I pose, either the lifetime over which we accumulate the wealth for our retirement, or the lifetime of the infrastructure of civilization and industry – decades. Beyond these time scales our ability for collective rational thinking and action is weak. Addressing the climate change problem requires us to face this weakness. It requires us to make knowledge-based decisions that are ultimately for the benefit of others. We will see a lot more carbon dioxide.
Here are the links to the Attribution series. I will return to that next time.
WU blogs on Attribution of Climate Change to Human Activities:
WU Blog on Models and Attribution