A Risk Assessment Approach to Climate Change Policy This is the first article of a five part series.
It is difficult to find a more hotly debated public policy issue today than the one about potential regulatory actions related to global climate change. Much of this debate is emotional focused on various groups' attitudes toward government action and personal responsibility, pessimism or optimism related to human interactions with the environment, and other philosophical differences. That being what it is, I think a different approach could show us the way out of that kind of divisive argument and produce positive action in an amount properly proportional to the nature of the threat. So, in a series of 5 articles, I am going to address this issue, not as a politician or a policy advocate, but as an engineer considering options and trying to reduce the risk associated with a particular problem. To maintain the non-partisan nature of this series, I am going to assume that increases or decreases in global temperatures are equally likely, and since, in theory, they have related solutions, it does not diminish the outcome of the analysis.
First, in this article, I will address the determination of the problem statement, and identifying the causes of the problem. The following articles will address finding the root cause of the probem, evaluating uncertainty and probabilities, evaluating the effectiveness of solutions and the reasonableness of their costs, and staying focused on legitimate end goals.
So, is climate change really a problem? Let's restrict ourselves to a discussion of changes in average global temperatures just to make this manageable. The Earth has experienced a variety of climates in the distant past from ice ages where the planet was significantly colder than today and warmer periods with higher temperatures than today. In its very early history, more extreme temperature variations occurred, but life on the planet was either non-existent or significantly different than what it is today. But in the past 400,000 years, the time period we have the most data on and where the plants and animals are most similar to today's, temperatures have varied between +2.5 C and -8 C compared to current values. Life goes on. The species of plants and animals have adapted to the changes with some kinds going extinct, and new species emerging. While this is certainly environmental change, it is not environmental destruction. So, let's cast aside that concern as being the problem.
But, more recently, in the last 6000 years, something has changed, with humans anyways. In a word: agriculture. Rather than a planet sparsely populated by nomadic bands of people hunting animals and gathering plants for food, we have a planet densely populated by humans living in cities and cultivating a large amount of the available land for food crops. If the Earth were to warm or cool significantly, the land available for and the productivity of our agriculture could drastically change. That could cause all kinds of problems for national governments with massive movements of refugees, not to mention food shortages and the suffering that goes along with those, and that is a problem. So, changes beyond +/- 1.5 C would cause a costly problem that we would be forced to eventually address as a crisis or a series of crises.
There is, of course, the potential for other things to happen depending on the severity of the change in temperature, but effects on agriculture is enough to consider for now. We just have to determine whether it is a problem or not at this stage, and I think we can say that it is for any significant temperature change up or down.
So, what could cause a change in the Earth's temperature? There are several things to consider. And, as in root cause analysis, we have to consider all of them, no matter how seemingly inconsequential to avoid leaving out a potential avenue for a solution. These will all be reflected in our intial cause diagram shown below. First, radiation received directly from the Sun provides the primary energy input to the system. 
Second, the core and molten interior of the Earth is warm due to the inital formation of the planet combined with radioactive decay of some elements. Third, although insignificant by most measures, other astronomical sources including other stars, distant galaxies, and even Jupiter and other planets and the moon provide some energy input to the Earth releasing radiation however small in our direction. Fourth, the reflectivity of the Earth causes some received radiation to be reflected back out into space affecting the energy balance. And fifth, the emissivity of the Earth affects how much energy is released from the Earth back into space (at night when the surface cools, for example).
Furthermore, to really determine if this is a problem worth devoting effort to solving, we have to consider the likelihood of this event happening. Since, there have been at least 4 complete cycles from the minimum temperature to the maximum temperature in the last 400,000 years, it is safe to assume that the cycling will continue whether or not we intervene. That means that we should expect the temperature to change by at least +2.5 C to -8 C from present conditions over the long term, and we will have to face the potential of that event as a society whether now or later.
So, climate change whether up or down, while not a true environmental problem, is a problem in terms of what human civilization is adapted to. In order to address that problem we have to attack one or more of the causes outlined in our diagram of the Earth's energy balance. The next article in this series will address how we choose which aspect to affect.