It seems the topic of global warming is constantly in the news due to big weather events, continued study and surveys on the issue, and the political agenda of many across the world. I think both sides can agree that the earth has warmed over the past 100 years.1 So that is a moot point. The real issue is what role does human activity play in the process? Climate scientists have used computer modeling for decades as one way to try to answer this question.2 To simplify this let’s use a simple algebraic equation, 400 = x + y.
Here the number 400 represents the measured historical record of the temperature of the earth. The x variable represents the overall contribution of natural causes of warming including things like naturally occurring CO2, cloud formation, solar radiation, and soot from volcanoes. Likewise the y variable represents the overall contribution to warming from human sources like fossil fuel combustion, soot formation, and deforestation. Modeling suggests the historical record of temperature variation over the past 50 – 100 years cannot be explained on the basis of just the natural variables.3 This implies humans have affected global warming. The problem occurs when one looks at the details of these models. Going back to our simple equation one should note there are multiple (x, y) combinations that are solutions. For example; (200, 200), (100, 300), (350, 50), and (400, 0) are all valid solutions. What is the true balance between natural causes and human causes of global warming? Is it 50:50? 80:20? 100:0? When one looks at estimates of the global carbon balance there is a total annual inflow of CO2 into the atmosphere of 157.5 billion tons. The estimated human contribution is 7.1 billion tons or 4.5% of the total.4 Chemical equilibrium studies suggest that of any new carbon dioxide added to the atmosphere at least 80-90% of it is reabsorbed, largely byplants and the oceans. In this simplified treatment we are also ignoring some important variables like water vapor, solar radiation, and effects due to the little ice age.5 Can humans really be the primary cause of the current planetary warming trend? Taken on the whole it does not seem very reasonable, but is more driven by politics than by science.
1. For example, see http://junksciencecom.files.wordpress.com/2012/07/6a010536b58035970c01761657c94f970c.png (accessed 2013.04.11)
2. Summary for Policymakers, The Third Assessment Report of Working Group I of the Intergovernmental Panel on Climate Change, 2001, p. 8.
3. ibid, p. 11.
4. Eubanks, L. P., Middlecamp, C. H., Heltzel, C. E., and Keller, S. W.; Chemistry in Context, 6th ed. McGraw-Hill, New York, 2009, Ch. 3.
5. Robinson, A. B., Robinson, N. E., and Soon, W.; Environmental Effects of Increased Atmospheric Carbon Dioxide, Oregon Institute of Science and Medicine, http://www.oism.org/pproject/s33p36.htm