Yep, it's getting warmer

In a recent issue of Science a trio of scientists who are experts on climate modeling and interpretations of data related to global climate summarize the best available information on variation in Earth’s surface temperature over the past half century or so. Their work addresses a controversial subject that those resisting the idea of global warming love to talk about.

Doubts about the reality of 20th century warming have been fueled by a veritable blizzard of misinformation and outright denial by politicians such as Senator James Inhofe and talk show hosts such as Rush Limbaugh and Glenn Beck. The political winds from the extreme right have been blowing so mightily against the notion of global warming that the front-runners in the race for the Republican nomination in 2012 seem to be obliged to join in the denialist chant. The American people are being deluged with misinformation and outright lies on this topic. It is thus worth thinking about the significance of this recent work by Santer, Wigley and Taylor.

One of the most difficult challenges in the entire business of drawing conclusions about Earth’s surface temperature is that there really is no single literal measurement that gives us the temperature of the planet. I wrote about this in Chapter 9 of my 2003 book, Making Truth: Metaphor in Science. When we want to measure our own body temperature, we insert a measurement device such as a thermometer, or one of the fancier digital probes, under our tongue, in our ear or up our rectum, as the case may be. The temperature we record in this way we take to be representative of our body as a whole. This works because our bodies are designed to maintain, as closely as possible, a single temperature throughout. But planet Earth is not like that. As I write this in Estero Florida the temperature is about 80 degrees Farenheit. At the same time, my daughter living in mid-central Illinois reports that the temperature there is about 11 degrees Farenheit. It is far colder still in Antarctica. No single value represents the surface temperature of the planet . For this reason, when we talk about the surface temperature of the planet we are using metaphorical language and thought. We talk aboutEarth’s surface temperature as though the planet were a small, temperature-controlled thing like a human body or a refrigerator.

To get to something that resembles a single value for the surface temperature, scientists began with simply averaging the temperatures measured at as many places as possible at the same time, and averaging over time as well. Before the modern age of satellite measurements the estimates were pretty crude. Consider that something like 70 percent of Earth’s surface is covered with water. How do we get sufficient measurements of the vast and varied seas to produce reliable numbers? And what about remote places that are not readily accessible, or crowded urban areas where human activity generates a good deal of local heat? With satellite measurements it has become possible to collect data over a short period of time that reflects surface temperatures
over most of earth’s surface. By averaging these in a suitable way, one ends up with a single number that we call the surface temperature of the planet. It’s a metaphorical entity, not a real single temperature, but its value over time can serve as a reliable measure of the change at Earth’s surface. However, the interpretation of satellite data is not entirely straightforward. A group of scientists at the University of Alabama at Huntsville concluded in 2005 from satellite data that the planet’s surface temperature had declined since 1979. This unexpected result was used to cast doubt on the reality of surface warming.

One of the hallmarks of good science is that controversial results are subject to reevaluation and continued exploration. The satellite measurements were a new technology, and many factors needed to be taken into account in interpreting the data. Climate scientists at a California laboratory identified two serious errors made by the Huntsville group in their analyses. These were acknowledged by the Huntsville scientists, who redid their recalculations. The corrected results showed a warming trend over the entire period 1979 to present. The revised estimate, following from critical scrutiny by other scientists, represents another step forward in our ability to measure and understand the evolution of the global climate.

Modeling the terrifically complicated global climate system is difficult. The challenge is to find a model that reproduces the historical record as well as possible, considering all the uncertainties,and then to use that model to forecast the future course of climate change, assuming various scenarios regarding levels of greenhouse warming gases, energy consumption, population growth and so on. The media are filled with confident pronouncements, for the most part self-serving, about climate change from political, ideological and financial interests. When we hear what people like Rush Limbaugh, James Inhofe or Newt Gingrich are saying or are ready to get behind, we need to ask what motivates them and what is their competence to speak on the issue at hand. We should also do that with respect to scientists, whatever the issue might be. Citizens need to go behind the one-liners of politicians and talk show personalities to learn what scientists think and the evidence that supports their views. There is no scientific conspiracy to deceive the public into believing that global warming is real, and that it has the potential to cause a great deal of human suffering. Scientists are just doing their work, trying to learn more about the way the world is.

An incredible amount of research across many scientific disciplines leads to an unambiguous result: the planet is warming, mostly because of increased concentrations of so-called greenhouse gases in the atmosphere. Denying this may be politically or financially expedient, but global warming is underway and it will gain strength with each passing year. How much adverse change occurs over the next 50 years and beyond will depend on whether humanity collectively decides to do something about continued generation of greenhouse gases. There is little hope for significant action in the near future. The 2011 Climate Change Conference in Durban, South Africa, just concluded with essentially no progress in setting mandatory goals for reductions of greenhouse gases. This should not surprise anyone. We humans have evolved to possess a strong consciousness of the future, but we still live very much in the present. Our proclivity to discount the future, particularly one so distant that we will not be there to live in it, prompts us to choose present needs and desires over future consequences of our actions. That seems to be the way it is with respect to climate change. As Kurt Vonnegut was fond of saying, “So it goes…”.

Weather, Climate and Global Warming

In my most recent blog I made mention of the common fallacy of drawing conclusions about the reality of global climate change from observations of local weather. Climate change denialists like to bring up the cold, wet summer or an unusually heavy snowfall during winter as evidence against global warming. But, as I pointed out, weather and climate must be understood differently. Weather is highly changeable on a day-to-day basis. Climate can also vary, but it does so on much longer time scales. It is quite possible that in a given year some large scale measure of climate, such as hurricane intensity, or rainfall over a large area, will move in opposition to a longer scale trend. But for the most part, changes occurring over a period of time such as a year will tend to show behavior that follows the long term trends.

I was therefore pleased to see the piece in this Sunday’s New York Times by Andrew Revkin that deals with the trends in record high and low temperatures across the United States over recent time. The data illustrate nicely that while record highs and lows continue to occur, the number of record high temperatures is increasing year by year, whereas the number of record lows is decreasing. The video in the piece, by Gerald Meehl, provides a nice explanation of what is going on.

Changing minds about climate change

One scientific question that has relevance for every person on the planet is whether the global climate is changing in response to human activities. The major causative agents of the change, if indeed there is change, are the so-called greenhouse gases. Some of them, such as carbon dioxide, methane and nitrous oxide, are naturally occurring components of the atmosphere, but humans have caused their concentrations to increase greatly. Other greenhouse gases are substance that humans have learned to make and use for various purposes. These include the so-called chlorofluorocarbons and hydrofluorocarbons.

Not everyone is convinced that human activities are the driving force for some of the climate changes we have been seeing in recent years, or that the scientific models for climate reliably predict what may happen in the future if we continue to consume fossil fuels and add increasing amounts of other greenhouse gases such as methane to the atmosphere. In one sense this is not entirely surprising, because climate is not a well-defined entity, not easily described in terms of just a few critical measurements. Weather, something that happens at the local level, and climate, which extends over large regions and ultimately to the entire planet, are easily confused in many peoples’ minds. Although seasonal weather changes from one year to the next are not reliable indicators of climate change, they are frequently brought into discussions as though they were. Thus, a cold spring in the northwestern states of the United States are taken by many as evidence that global warming is not occurring. It seems that nearly everyone is an expert of some sort on climate. Political entertainers such as Glenn Beck and Rush Limbaugh, who have not a shred of expertise, don’t hesitate to declare that global warming is a massive hoax perpetrated by an establishment that wants to use it as a pretext for sinister incursions into private rights and freedoms.

This is a big topic, because if climate changes are occurring as a result of human activities to date, those changes will accelerate greatly over the next few decades as more and more greenhouse gases are pumped into the atmosphere. I need not rehearse here again, as I have in earlier blogs, the vast range of studies performed by scientists working in many different disciplines, and in a host of environments all over the planet, to attempt to learn about past climates and the changes occurring now in our own climate. Those studies have all gone into formation of the successive reports of the Intergovernmental Panel on Climate Change (IPCC), and the information collected there is continually updated as new evidence is produced. All of this scientific work, and the inferences drawn from it by the best minds working in all the areas of science related to climate change, have led to the conclusion that the climate is indeed changing as a result of human activities, and that the changes are accelerating. For example, the Greenland ice mass is decreasing; the latest evidence is that the loss is accelerating.

This past March, a group of about 2000 climate scientists gathered in Copenhagen to assess the current views on climate change. Because the group was not brought together under the auspices of the IPCC or any other single governmental agency, participating scientists were more free to offer frank appraisals and prescriptive statements. Many factors that bode ill for our prospects were either not considered in the IPCC report or were very conservatively estimated. For example, it is only now becoming evident that permafrost holds vast amounts of carbon that is becoming “unlocked” as the permafrost warms. The upshot is that the prospects look worse than the projections of the IPCC would lead one to expect.

The evidence for global warming and the role of human activities in the process, is at this point overwhelming. One way of putting this is that there is a strong consensus in the scientific community on these matters, of the same sort that exists with respect to many widely held bodies of evidence in chemistry, physics, genetics, and other branches of science. The National Academies of Science have produced a very nice video, America’s Climate Choices, that reveals the degree of consensus that obtains in the scientific world, and describes the organization of groups of experts that are being convened to assist the government in addressing the challenges that lie ahead. I urge you to watch this, to sense how deep and widely felt are the views of outstanding scientists and other citizens on this matter. Yet there are scientists, mostly without credentials in any of the relevant areas of science, and lacking acceptable scientific evidence that contravenes the current understanding, who continue to reject the consensual scientific position. Some seem to think it is a conspiracy of some kind, an attempt to somehow put something over on society. I can understand how some politicians, entertainers, entrenched interest groups such as those representing certain segments of the energy industry and the like, might find it convenient to resist the existing scientific evidence, but what is going on in the heads of deniers who have a supposedly scientific training? It must have to do with a deep-seated unease with the implications of greater governmental oversight as society comes to grip with the steps that must be be taken to reduce greenhouse gas emissions and at the same time begin to deal with mitigating global warming effects.

In a letter published in a recent issue of Chemical and Engineering News a writer reluctantly seems to agree that Earth’s climate is getting warmer, though he cites the low spring temperatures in the northeast as evidence that might contradict the global warming hypothesis (!). But he thinks that “blaming it (global warming) on human activities seems to be speculative.” What blows my mind is that this person can’t seem to imagine that the virtual army of scientists working on this problem would not have held this very question at the fore in all their work! What does that say about this person’s understanding of how science works? Apparently the means by which science establishes its epistemic authority, within the scientific community and outside it, is not clear to some scientists. We have a long way to go.