The floor was opened for questions. A strained voice burst from the anxious throng: "Point four degrees per decade is the highest rate of increase of global temperature in history. Do you have any idea what that means!"
Well, no, I don’t. But I wasn’t being asked. The words were directed to the speaker who had just given a routinely alarming, doom-cliched presentation on global warming. If it were my question to answer, I might have said, "When I switch on my night stand lamp, temperatures nearby increase by more than that before I get my feet up and open a book." I also might have said that such an increase is too small to show up on most thermometers.
I could have suggested Valium, too, but I’m not that kind of doctor, and it might be rude. I also would not reveal a dark secret that I share only with close friends and family: There is no such thing as global temperature. And if there is no global temperature, how can there be global warming?
But last summer I was found out in Santa Fe. It happened at a climate research conference, where I was invited to speak on another topic. At the conference dinner, one participant stood up and exposed my global temperature denial. The room erupted into chaos. I started eyeing the exits and sinking under the table. I imagined there were calls for a rope, as the crowd of scientists seemed to teeter toward becoming a lynch mob.
But my fears were not realized. It wasn’t the Wild West after all. The crowd settled and a scientist at my table asked me why I objected to global temperature. I replied minimally, "on physical grounds." To my surprise, my interrogator simply nodded and accepted the explanation. He obviously knew the physics. However, he said, "but an average over temperatures is OK to use as an ‘index,’ isn’t it?"
"Well, er, yes. I suppose it’s OK," I replied. But if increasing temperature means "warming," what does increasing "index" mean? Global "indexing"?
My dark secret needs little explanation for thermodynamically minded people. For them, it is really quite simple: The Earth is not in "thermodynamic equilibrium," so there is no single temperature for the whole thing. No statistical hocus pocus can change that. However, global warming proponents and skeptics alike have been very busy averaging temperature data, unsupervised, on an industrial scale for years.
A few years earlier, after a lecture on averaging temperatures for climate purposes, I questioned the statistician who made the presentation. What do his averages mean in terms of physics, I asked, given that averaging temperatures is not physical. Apparently no one had asked him that before.
Many people think that you can make sense out of an average of anything at all. My usual reply is to ask what an average over telephone numbers means.
Temperature is like that. When averaged, it does not produce an actual temperature of anything, any more than an average over telephone numbers must be a callable number, let alone a number you might care to call.
The statistician, knowing what I was getting at, said that he would think about it. Recently, at another event, he sat down beside me and said, "You know that question you asked me a few years ago? I have been thinking about it ever since, but I still don’t have a good answer for you." Then he excused himself, and left with my greatest respect.
Even when I make the case successfully, recidivism is rampant: The mad purist says it isn’t strictly temperature, but maybe it’s sort of like temperature.
It isn’t even a sort-of-like temperature! Thermometers measure the temperature from where the thermometer is and from nowhere else. Temperatures from elsewhere have nothing to do with it. But to be "global," global averages depend on temperatures from far away. As the recipe goes, you have to literally collect the temperature in Miami to decide whether "warming" is "affecting" people in Paris.
Oh, just to make it really interesting, that recipe also calls for temperatures in Miami from, for example, 20 years ago. So the climate index story actually is: Long ago and far away, there was a single lonely temperature at a small unimportant airport that grew up to be so important that we all depend on it everywhere ever after. It is like saying that the ice cubes in your freezer are melting because Mike, down the block, lit his barbeque last summer. This "index" cannot possibly be a temperature with properties like that.
Not only is it not a temperature but temperature, even properly formulated, has the wrong character to understand what is going on. Climate and its change is about things that go: wind, heat flow, moisture flow, ocean currents, radiation etc. These are driven by differences — differences in temperature and differences in other things such as pressure. So you need at least two different values, not one, to make things go. A single global "temperature" is dead, dead, dead for understanding processes!
Why the obsession then with this single "temperature-number-index thingy" for everything?
Temperature is anemotional topic. It involves personal feelings, discomfort with technicalities and popular culture as much as physics. These feelings have forced my meteorology friends to "indexify" local temperature, too. This led a European scientist to ask me once why weather forecasts in North America reported exaggerated "temperatures."
Elsewhere, temperature is just temperature. But here, humidity is "temperature." And wind? Well, that’s "temperature," too. Wind and humidity are bludgeoned into something they are not to produce temperature-like numbers that are lower than real temperature when it is cold and higher when it is hot. Over here, we prefer our physics to be like an action hero: one-dimensional and exaggerated. It is a lot more fun to make small talk about how temperatures are a gazillion degrees.
When the global-average-temperature-index "thingy" goes out in public, all of the temperature baggage comes with it. Extraneous things are subjected to the tortured temperature treatment. Glaciers and hurricanes become temperature, so do frog, horse and human maladies, including pulmonary disease, delirium and suicide. Apparently the "thingy" can even be employed to follow evolutionary changes in squirrels and explain kitten numbers. It’s amazing what tenths of a degree can do.
-Christopher Essex is professor of applied mathematics and director of program in theoretical physics at University of Western Ontario, and co-author of Taken by Storm: the Troubled Science, Policy and Politics of Global Warming.