By David P. Gushee with David E. Gushee
Follow David P. Gushee: @dpgushee
David P. Gushee: In this column about climate change I am going to give the majority of the space to my esteemed father, David E. Gushee, who served for decades as an energy and environmental policy analyst for the federal government.
Dad and I have been dialoguing about the science, policy and ethics of climate change for a long time, but especially since I began weighing in on the issue as a Christian activist in 2005. I was the principal drafter of the Evangelical Climate Initiative (ECI) statement, which came out in 2006 and declared that climate change was real, was human induced, would have significant impact, especially on the poorest and most vulnerable of the world, and required a comprehensive personal, social, and policy response based on Christian theological and ethical commitments.
Much of the urgency behind ECI came from our taking seriously the findings of the Intergovernmental Panel on Climate Change (IPCC), which seemed then and seems to me now to offer a quite impressive example of international peer-reviewed scientific methodology. The IPCC has always had its critics, the loudest of whom have consistently claimed that some IPCC-related scientists have gotten out ahead of their data — or at least that public reporting on IPCC data oversells and oversimplifies the actual findings. Certainly the various dimensions of the periodic IPCC reports do not all operate on the same level. Reporting on current evidence of climate change is one thing; projecting future impacts is another; and proposing appropriate national and global policy responses today in light of all relevant factors and tradeoffs is a very different task, actually beyond the purview of climate scientists but deeply affected by their reading of their data, models, and projections.
The Obama Administration, unlike most Republican leaders today, trusts the majority voice in climate science, believes in the seriousness of future climate change impacts, and is undertaking substantial domestic and global policy steps that the administration believes are most likely to reduce or slow carbon dioxide emissions and thus retard global temperature rises and overall climate change. The most worried climate change activists are not satisfied with the steps being undertaken either by the US or the global community, and their warnings are sometimes quite apocalyptic. I recently read A Political Theology of Climate Change, by Scottish ethicist Michael Northcott, a book suggesting that human survival may be threatened, and before too long.
My father, who is a scientist and who follows the data closely, is deeply skeptical about such alarming claims and very much wants his son (me) to avoid falling prey to scientific claims he deems excessively dire relative to the actual evidence. How poor bedraggled non-scientist religious leader types like ourselves are supposed to adjudicate disputes among scientists is not easy to discern. And if we must make decisions now that will certainly affect the well-being, if not the survival, of future generations, while also affecting the economic and ecological circumstances of today, is it better to err on the side of alarmism, or moderation? If we overcorrect, what are the costs and risks? If we undercorrect, what are the dangers?
What follows is a primer on just a few of the uncertainties in basic climate science, offered by my father to my readers. His comments certainly raise questions vis-à-vis climate news as it is generally reported.
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David E. Gushee: Fundamental to the debate about climate change and humanity’s impact on it is temperature and its measurement. Temperature is being used as the surrogate driving force for a lot of variables which together make climate. It is also being used as the surrogate driving force for the impacts of climate on life on Earth.
People have been measuring temperature for a very long time, including making and keeping records of those measurements. We all know that temperatures vary widely throughout the day and throughout the year. They also vary widely from sea level to mountaintop, from north to south. So a basic question is: Which, of all these temperature measurements, drives the climate? The issue is being presented to the people as: The average world temperature is the driver.
What is the “average world temperature?” It is a calculated number derived from all of the individual temperature measurements from all over the world (actually not all, but most, as some are viewed as not acceptable for one reason or another). It is not a natural number; it cannot be directly measured. It depends on all those individual measurements and how they are aggregated. It depends on what data points are not included for any of a variety of reasons. It does not include all those measurements not taken because there is no measuring device in those locations.
The scientists involved really try to compensate for all of these uncertainties, and individual recent measurements are probably more precise than earlier ones, but they are still not without some uncertainties.
Despite these uncertainties and the calculated variable of average world temperature, there is general agreement that the world is a bit warmer now than it was a hundred or so years ago. There is also general agreement that there have been decade-long periods where the world temperature trend has been up, periods when the trend has been down, and periods when it has been stable. This variability of world average temperature over time underlies one of the fundamental questions about climate: Is the most recent period of upward trend caused by increasing carbon dioxide concentrations whereas earlier upwards periods were not so caused?
Last year’s average world temperature was reported with two significant figures after the decimal point. That is more precise than the individual measurements are. The change from the previous year was reported as an increase of about one twenty-fifth of a degree. The error estimate for both this year’s average temperature estimate and last year’s is about twice that difference. That means that the claim that 2014 was the hottest year in a long time and hotter than 2013 is like saying there were a few more angels dancing on the head of the 2014 pin than on the head of the 2013 pin. Despite the government agency press release and the wave of news reports based on it, the underlying agency report made clear that the claim made so definitively was as likely to be wrong as to be right, even though it is true that, based on calculated world average temperatures, both years were among the hottest in recent history.
Average temperatures do not create weather. Weather is driven by, among other things, temperature differences. Temperature differences, among other factors such as altitude, create pressure differences. Air flows from areas of higher pressure to areas of lower pressure. If climate is weather over time, then the variable of interest is not the average temperature, but all the temperatures, as creators of pressure differences, air flow patterns, humidity, and lots of other variables.
Is there a relationship between the effects on climate of the totality of temperatures and their differences and the effects on climate of changes in the “average” temperature over time? No one knows for sure, but the premise in the current climate change debate is that the average can be used as the climate-driving variable for policy purposes.
There’s not much doubt that carbon dioxide is a greenhouse gas, but there is a lot of doubt about the sensitivity of temperature to its concentration. The models use a sensitivity of about 3 degrees Centigrade per concentration doubling, whereas there are peer-reviewed papers showing sensitivities as low as one degree. The evidence is not clear that any of these sensitivities is more provable than any other, but the conventional wisdom uses the 3 degree estimate.
Other factors affect air and water temperature besides carbon dioxide. Water vapor (clouds and humidity) is a major one. So also are solar energy input, other energy waves from space, other components of air (particulate matter, for example), land surface characteristics, etc. Interactions among these factors are incompletely understood.
The models all assume continuous temperature increases; data over the last 20 years or so show a current period of stable temperature which the models did not predict. Hence, all the models are currently overestimating short-term global temperature increases compared to the data. The modelers have not yet been able to identify, quantify and incorporate into the models the factors which have led to the observed changes in temperature over time. As the current period of stable temperatures continues, the models will continue to overestimate the long-term temperature path until they are modified to include variables which would be able to predict temperature paths other than continually rising, which would then come to pass. Since the climate change issue is the result of inferred long-term impacts from implied continuing temperature increases, which the models continue to predict but which over the past two decades or so have not occurred, the basic policy question is: How should the policy response recognize the uncertainties surrounding the definition of the policy question?
One of the consequences of continually increasing temperatures would be the melting of glaciers and a resultant increase in sea level. There is a great deal of uncertainty in measurements of sea level, but it is clear that sea level varies widely from place to place and from time to time. There is also indisputable evidence that ground levels change over time, rising in some places and subsiding in others. This creates uncertainty about the meaning of “average sea level.” Evidence about glacier melt is equivocal, with some data series showing that it is increasing, but other data series showing trends in the opposite direction, all over relatively short time periods compared to the long-term concern. The essential point made by the advocates is that temperatures are sure to continue to increase and thus glacier melt will irreversibly increase, thus leading to sea level rise.
There also is no doubt that warmer water temperatures cause water to expand, which would cause sea level to rise. Just as there is uncertainty about what the sea level is and how it is changing, there is also doubt about sea water temperatures and their trends, as there are large holes in the data and uncertainties about the accuracy of existing data series. Water temperatures, like sea levels, vary widely over time and place. Much is not known about the causes of these variations. There are many factors besides air temperature that affect sea water temperature — the Earth’s wobble (deviation from a stable rotation), basin to basin flows, underwater volcanoes, and time of year, to name a few. As a result, aside from generalizations from the assumption that temperatures are sure to rise, there is no way to know anything quantitative about water temperatures and thus impacts on sea level. Estimates vary widely; uncertainties abound.
In sum, the theory that carbon dioxide is the control knob for global temperature, the fact that the world’s average temperature is calculated to be a bit higher than it was a while ago, and the fact that carbon dioxide concentration is increasing and is almost certain to continue to increase underlie the whole climate change debate. The theory has been shown to be incomplete; the average temperature has not increased for 20 years while the carbon dioxide concentration has continued to increase. This divergence between theory and data remains subject to intense debate. More and better data are being gathered, but the unknowns remain unknown.
