What’s in a name? / Climate Change / Global Warming

What’s in a name? / Climate Change / Global Warming

For those interested in the trip to Copenhagen discussed in the last blog, or those who are using the blogs in their classes, then see below.

I did a series of blogs from a meeting on climate and public health in Goa, India. The question was posed at the beginning of the meeting - Will someone please explain the difference between climate variability and climate change? I was recently talking with Jerry Mahlman about the terms “climate change” and “global warming.” Jerry was saying that using the term “climate change” was, well, wimpy – perhaps politically expedient. “Global warming,” he maintained, is a better term because it is concrete, conveys information, and describes the basic consequence of carbon dioxide pollution. These are all fundamental words with meanings that, now, permeate politics and business discussions; they extend far beyond the confines of the community of climate scientists.

There is always variability in the climate; hence, the climate is always changing. If you wanted to take a scientist’s point of view, then first you would have to define “climate.” Climate has traditionally been defined as average weather, but climate is far broader than temperature and rain, the usual measures of weather. (Here is a previous blog on the subject.) For the sake of argument, however, define “climate” as the average temperature of the surface of the Earth. The first question is then how do you define the average – 1 week, 1 month, 1 year, 10 years, a century? For a variety of reasons climate got defined as a 30 year average of weather. Another question might be – over what area of the globe do we average? In this case we have chosen a global average, so the whole globe. There are many arguments about what is the appropriate average, and in particular, as we have observed the ocean and understand the ocean’s role in climate, a 30 year average is pretty short. For this blog, however, we can define the climate as an average of the global surface temperature, and climate change means that the global surface temperature changes with time. The mathematically oriented would say there is a time derivative of average global surface temperature.

Given an average temperature, we would expect there to be variability above and below this average. That is, one year is different from the next. This variability comes from all types of causes – natural and human-caused. Natural variability is often attributed to changes in the energy that comes from the Sun or volcanic eruptions. But there is a lot of variability that is associated with “the weather.” Here I use weather in a generalized sense that also contains natural ocean-atmosphere variability such as El Nino, the Pacific Decadal Oscillation, and the North Atlantic Oscillation. (see this blog and this blog for more information on such variability.) Human-caused changes in the global averaged surface temperature come from, most prominently, greenhouse gases and changes in land surface – trees versus farms versus parks versus parking lots.

Even in the best of worlds, scientists have to worry about how to determine what variability is “natural” and what is “human-caused?” This is the attribution problem, and here is a link to a whole series on attribution. Also though, you have to worry about whether or not we have experienced and measured all climate variability? The answer to this question is, obviously, no. We know there are ice ages and previous times when the Earth was much warmer. This brings another attribute to the definition of “climate change,” that is, the human dimension. From a practical point of view we are interested in is the climate changing at a rate than matters to humans? Civilization has developed in a temperate climate with stable sea level.

Climate change, therefore, could be viewed as whether or not the average weather is changing or whether or not climate variability is changing – perhaps, whether or not the average is changing to lie outside of the “normal,” or observed, variability. Given the challenges of defining climate as “average weather,” it is almost certain that the climate is changing, irrespective of what humans are doing.

Some would argue that “climate change” became the term of choice because it was acceptable in decent company. We could all agree that the climate is changing, but to say that the globe was warming was a value judgment, a conclusion, that was more definitive. It was a statement that could cause a reaction that would “end the conversation.”

Yes, I recall during the 1990s something of a search for the simple “one word” description of climate change. Aside from “global warming” being, perhaps, politically divisive, there was the idea that it was “too simple.” I have also had the conversation with Jerry Mahlman that the real problem was water, water resources, and sea level rise. Global warming “of a couple degrees” was not so threatening; in fact, some would make the argument that people prefer a warmer climate. Hence, to talk about warming diverted the conversation away from the real problem. So “climate change” is also a term where people migrated to include not only temperature, but water, and permafrost, and sea level, and ice sheets, and sea ice. You could bundle it all up.

I work hard in this blog to walk the line between complexity and simplicity. What term, what metaphor, what concept is simple enough to explain what is happening, but complex enough to embrace adequate complexity to be meaningful? Presuming a devoted and diligent readership, you might have noted that I have moved towards “global warming,” or the “consequences of a warming planet,” or “water in warmer environment.” It’s a little like the attention that I try to give to “the scientific investigation of climate” instead of “the science.” We know enough and the consequences are large enough that we do need to make the concrete statement, the value judgment – we know the sign, the surface of the Earth has and will warm.

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It’s been busy and I have been slow on the blogs. At the top of the list of busy is the Conference of Parties in Copenhagen in December. This is the fifteenth such meeting. It’s a show, where there is an attempt to build policy. The official focus of this will be beyond Kyoto. To some of us, it never really felt we got to Kyoto, but … Also every advocacy group in the world, both for and against will be there. The University of Michigan and Alma College will have a delegation there of about 40 people … students, faculty, alumni and affiliates. The students have done OK raising money. Now we need to find rooms.

Several people have told me they use these blogs in classes. Laura Bell and I have set up a data base that uses a simple faceted search to organize the blogs. It’s built on mediawiki. Have a look, and let us know if it works and how it could be made better. (climateknowledge.org/Blogs)



Figure 1: Sky at Vedauvoo Rocks, October 2009