Climate Q & A

What is “climate”?

The American Heritage Dictionary says: “1. The meteorological conditions, including temperature, precipitation, and wind, that characteristically prevail in a particular region.” That’s a pretty good answer, actually, because it’s the long version of “climate is the average weather.”

It’s important in talking about this to distinguish between the global climate and regional climate. The dictionary definition is obviously related to the latter, and the global climate is just all the regions averaged together. But, as we all know, the regions differ widely among themselves. If you ever have to choose between living on the North Slope of Alaska or in a rain forest in Brazil, these differences will become an important thing to think about. (Extremes such as this make living in the Southwest pretty attractive.)

A longer and more detailed discussion of climate (including some graphs of temperatures in the Southwest) is included on our Climate Fundamentals page.

What is the Greenhouse Effect?

What we call the “Greenhouse Effect” is a natural climate process that keeps the global climate of the Earth about 60oF warmer than it would be otherwise. It’s named, somewhat erroneously, after the way a greenhouse works. Sunlight shines through the windows and warms up the interior. But the glass in the windows keeps the radiant heat from the warm greenhouse from escaping to the outside and cooling the greenhouse off.

Various gases in Earth’s atmosphere—in order of importance to the process these are water vapor, carbon dioxide, ozone, the various oxides of nitrogen, methane, and the fluorocarbons—do the same thing to the climate. They let sunlight in and keep Earth’s radiant heat from escaping to space.

The Greenhouse Effects gets lots of publicity these days because our use of petroleum and coal for fuel, among other things, is putting more and more carbon dioxide into the atmosphere. This will tend to increase the strength of the Greenhouse Effect and warm things up. By itself this would be no big deal—that is, it wouldn’t warm things up very much—but other processes in the climate system could amplify the carbon-dioxide related warming.

In particular, if a warmer climate puts more water vapor into the atmosphere, the water-vapor related Greenhouse Effect will warm things up even more. This is an example of positive feedback. Other climate processes, such as the effects of clouds, could have the opposite effect and create negative feedback, helping to moderate the changes.

Unfortunately, the Greenhouse Effect, a single process, is often confused with Global Warming, a possible result of all climate processes.

Is Global Warming happening?

Like most simple questions posed to scientists, this one is hard to answer in a simple way. The short answer is “probably.” The long answer is, unfortunately, long, convoluted, and still equivocal—that is, it has ”probably”s in it, too, as well as a bunch of “maybe”s. And a simple “yes” or “no” answer to this question isn’t very helpful anyway, because what we really need to know is “how much?”

For the past few years, the most authoritative set of statements on the subject is from the 1995 international report on the issue:

“The limited available evidence from proxy climate indicators suggests that the 20th century global mean temperature is at least as warm as any other century since at least 1400 AD.”

“Most of these studies [of the statistical significance of temperature changes] have detected a significant change and show that the observed warming trend is unlikely to be entirely natural in origin.”

“...the balance of evidence suggests that there is a discernible human influence on global climate.”

(Intergovernmental Panel on Climate Change, 1995)

Not a very satisfying state of affairs, is it? Well, here are more quotes, from the most recent report:

“An increasing body of observations gives a collective picture of a warming world and other changes in the climate system.”

“Emissions of greenhouse gases and aerosols due to human activities continue to alter the atmosphere in ways that are expected to affect the climate.”

“There is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activities.”

“Human influences will continue to change atmospheric composition throughout the 21st century.”

“Global average temperature and sea level are projected to rise under all IPCC SRES scenarios.”

(Intergovernmental Panel on Climate Change, 2000)

(These statements are taken from the summary sections of the IPCC 1995 and 2001 reports, they were strengthened significantly in the 2007 report. They are straightforward and not used out of context here; even jargon has been retained. For example “proxy” climate indicators are such things as tree rings, which can be used to infer past climates in a reasonably quantitative fashion. Not as quantitative as a real thermometer, maybe, but such indicators have been studied to the point that they are well understood. And “statistical significance” is, well, statistics jargon that refers to how certain one can be that a particular statistic isn’t just random chance. In the last quote, “SRES” is the Special Report on Emissions Scenarios, which discussed the various possible sets of future greenhouse gas and aerosol emissions used in various model studies.)

It is interesting to compare the two sets of statements, made by an international group of climate scientists five years apart. In the 1995 statements, the last one, that human activities appear to be having a discernable influence on climate, raised a firestorm of criticism and controversy. Yet, after five more years of additional study and analysis, the statements from the 2000 report are even stronger. If this trend continues, global warming will become a solidly accepted fact of life in the research community within the next few years.

In any case, a more relevant question, especially for the Four Corners is...

What will happen in the Four Corners region as a result of Global Warming?

Again, there is uncertainty in any honest answer to this. There are two sources of information relevant to this question. One source is historical records of the climate of the past, and the other is computer simulations of the climate of the future. It’s important to remember that the Southwest is BIG, so it may be that different parts of the region will experience different changes. Generally, though, putting all the information together suggests that it will become somewhat warmer, especially the winters, and possibly wetter, although the question of precipitation is not at all settled.

One problem with making regional climate change predictions is that computer models do not agree on what will happen in the future. This is probably because these models are not designed to focus on the specific weather processes that dominate the weather and climate of the Southwest. For example, much of the precipitation here is affected by the presence of mountain ranges. But the climate models do not represent these mountains at all well. Consequently, their representation of rainfall and snowfall in the Southwest is not especially faithful to reality. Consequently, they do not agree well on our future climate.

Nonetheless, the value of this information, uncertain though it may be, is that it provides us with time to plan ahead, so that we can adapt to what may be coming.

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Copyright ©2000, 2010 Howard P. Hanson.