Models and Planning for Climate Change
Models and Planning for Climate Change
I have written many blogs about models and modeling of climate. My collection includes a 2012 tutorial approach where I show that climate modeling is the process of calculating a budget, with many similarities to keeping the balance of a checking account (Introduction and end). In 2012, I wrote a piece on uncertainties in models and a number of ways to evaluate and to place model uncertainty in decision making. In 2011, I wrote a piece about the controversial subject of validation of climate models.
There is regular publication of papers about models, their evaluation and their potential usefulness in planning for climate change. I want to mention a couple of them in this blog. The first is a paper by Elisabeth Lloyd, who is a philosopher at the University of Indiana. ”In Confirmation and Robustness of Climate Models”, Lloyd investigates the robustness of climate models in a formal way. Robustness is related to a set of common outcomes that follow from model simulations. In this case the common outcome is that given an increase in greenhouse gases, then the set of models determine that the average surface temperature of the Earth will rise. Underlying this determination of robustness is the fact that all of the climate models are designed to represent the laws of physics that represent the balance of energy (see the tutorial series). There is a requirement that “greenhouse gases relate in a law-like interaction with the energy budget of the earth.” Then, given the fact that the representation of these laws by a number of models from independent research organizations leads to the same outcome, that the planet will warm, then it is very likely that these models are a robust representation of what will happen in the real world. The size of the temperature increase has meaningful uncertainty; however, that there will be significant heating is of little doubt.
Lloyd’s arguments are not simply based on the fact that all climate models say that the Earth will warm as greenhouse gases increase. Lloyd lays out three fundamental ways to confirm the performance of climate models. The first line of confirmation is how well do the models fit the observations? This is the most common, most natural way of confirming model performance. How well a model fits the observations is, however, always open for arguments. There is always some difference between model simulations and observations. This difference fuels the arguments about whether or not the models are correct enough to provide actionable information (telescope simile in this blog). The other lines of confirmation that Lloyd relies on are varieties of evidence and independent support. Independent support is, basically, that sources of information that are fundamentally unrelated lead to the same conclusion. It is the convergence of all of these pieces of information with the fact that many models give the same basic outcome that supports Lloyd’s conclusion that robustness is a positive virtue in assessing the quality of climate models.
Lloyd’s conclusion is a formalized statement that if models consistently represent an outcome then we have more confidence that the model is correct, than if the models are inconsistent. As the regional details of model simulations are considered, for example what will happen to the water levels in the Great Lakes, models are often more inconsistent in their behavior. This inconsistency is a flag of uncertainty, or a lack of robustness. There are many lines of scientific and experiential evidence that increasing greenhouse gases will lead to warming of the Earth’s surface, the melting of water stored as ice and the rising of sea level. These conclusions are highly robust.
The other paper I describe is an opinion piece, ”Can We Trust Climate Models,” by J. C. Hargreaves and J. D. Annan. In this piece are a number of elements in common with the Lloyd piece, namely the discussion of the independence of models and information. They conclude that the broad predictions of surface warming, melting ice and rising sea level are robust because of their consistency with underlying physical principles. They also state that the models are not robust on regional scales.
Hargreaves and Annan add to the argument the idea of posing alternative descriptions, hypotheses and theories to describe observations of the climate. Climate models can be viewed in many ways. They are a mathematical description of our knowledge of the climate. They are also a way to organize and manage the complexity of describing the Earth’s climate and how it will evolve. What Hargreaves and Annan pose is that if the errors and uncertainties of climate models were too grievous, then they would invite alternative descriptions. Indeed, some of the pieces that make up a climate model do invite alternative descriptions, which is what drives model development and improvements. Observation-based, rational pursuit of alternative descriptions frequently lead to new insights about processes, for example, the partitioning of water in clouds between vapor, liquid and ice. However, the underlying principles of the model the conservations of energy, mass and momentum have proved to be quite robust. The observable and resolvable attributes of the climate, for example the fluid flow that describes the motion of the atmosphere and the oceans, which provide the connections between the pieces, have proved to be resilient against alternative descriptions.
Given the vast amount of observations of the climate and the thousands of researchers who have invested their competitive personalities in exploration and investigation of the climate, it is unlikely that fundamentally different quantitative descriptions of the Earth’s climate will be found. This assertion is supported by the successes of climate models, which have been confirmed in several independent ways. Affirming the successes of climate models is the ability of the models to present complex patterns of behavior that have been simulated, predicted and observed, making it highly unlikely that alternative explanations will be found of the changes being observed in the Earth’s weather and climate.
Is this actionable knowledge? The answer for many is an, obvious, yes, because people, corporations and governments are taking actions. What is missing in action is any rational, national or global approach to reduce emissions and, therefore, to bound the changes to our weather and climate as incremental changes to our history of the past few centuries. This leads to a situation where the actions that we take are in many ways temporary patches, because over decades and the next few centuries, we will be reliably warming up and sea level will relentlessly rise. There is much more difficultly predicting changes to ecosystems, agriculture, pathogens, political systems and nations. This will require anticipation, to which models will contribute, and the willingness and flexibility to spend on adaptive strategies if we are to obtain societal stability. Those who view models as providing actionable knowledge are more likely to succeed. Otherwise, we will be like those who lived on the shore of modern Turkey at the end of last glacial period, chasing the retreating glaciers and their water into the mountains with their goats and sheep (Sagalassos).
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I'm a professor at U Michigan and lead a course on climate change problem solving. These articles often come from and contribute to the course.
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