WeatherZine WeatherZine Number 10, June 1998
"What's happening on the Societal Aspects of Weather WWW Site."


Editorial"Normal" weather and climate

Community News Weather Research in NSF/Social, Behavioral, and Economics Research Directorate

New Additions to the WWW Site Subscription & Posting Information


"Normal" weather and climate

There has been a lot going on with the weather of late. Floods, fires, and heat waves have dominated headlines in recent weeks. Such extremes serve to focus public and policy attention on important issues like climate change and natural hazards. These events also provide an opportunity to reconsider how we as a society view our relationship with the atmosphere. One central concept that underlies day-to-day discussions about the atmosphere is "normal" weather. The way we talk about "normal" weather just might obscure a more accurate conception of weather and climate with important implications for the decisions that we make.

The term "normal" has different connotations when used in the context of weather and climate.


Over a human lifetime, one experiences a wide range of weather and becomes aware of even more through the media. This body of experience defines what is "normal." This is what Secretary of State Madeline Albright meant when she commented recently that "I have been on Earth now for 60 years, and I have never witnessed weather of the kind I have seen, read about, and heard about these past few years."


The familiar bell-shaped curve that we have all seen in statistics is also called a "normal curve." It is a mathematically precise description of a probability distribution. At the midpoint of the distribution (the top of the "bell") we find the average of a distribution. So when your local TV weather forecaster discusses the "normal" temperature for today, he or she means the average in a statistical sense, even though a wide range of temperatures might be considered "normal" (as in "typical.")


People have expectations about what sorts of weather are "appropriate" on planet Earth. When weather events violate these expectations, people look for explanations. For instance, in 1993 a U.S. Congress hearing was held to ask "has nature gone mad?" Debate on global warming has focused on whether climate might change in a manner that is not normal i.e., beyond "natural" variability.

When weather and climate experts talk about "normal" weather, they often mean this in a statistical sense. For instance, here in Boulder we have had above average (not normal) temperatures over the past week. But it is typical (normal) for a Colorado summer to see several such heat waves. So at once, the weather is both normal and not normal. Given such imprecise use of language, its not surprising that people get confused.

Others have identified this potentially confusing terminology (see, e.g., and Pielke, Sr. and N. Waage, 1987. Nat. Wea. Dig 12:20-22.) But it seems that the problem goes deeper than just terminology. The confusion over the use of the term "normal" underlies a more fundamental issue, that of climate stationarity.

We assume, as Al Gore has written, that "the earth's climate follows a relatively predictable pattern in the sense that even though there are constant changes, they always fall within the boundaries of the same overall pattern." This "overall pattern" whether defined experientially, statistically, or some other way sets the expectations on which climate- and weather-sensitive decisions are made.

But what if this overall pattern that we are used to is only a momentary pause in the earth's climate? In other words, what if changes in the overall pattern are themselves normal? What would abrupt and drastic climate changes (whatever their cause) mean for societies around the world?

What to do? Clearly, scientists and the media can do a better job of communicating what they mean when they talk about weather and climate, e.g., by using average when they mean average. But more broadly, with the input of climatologists, policy makers must become aware of the assumptions that they have about weather and climate and the role that these assumptions play in decision making. A place to start is by understanding "normal" weather and climate.

— Roger A. Pielke, Jr.

[ Contents ]

Community News

Weather Research in NSF/Social, Behavioral, and Economics Research Directorate

The National Science Foundation (NSF) is the one of the United States government agencies responsible for supporting science. NSF supports a considerable amount of research into the societal aspects of natural hazards and global climate change. With the help of NSF we are able to provide a list of NSF grants from its Social, Behavioral, and Economics Research Directorate that are focused on the societal aspects of weather. The list should be considered fairly complete, but not exhaustive. One of the goals of the U.S. Weather Research Program is to compile information from across the agencies on support for societal impacts research. Such a "cross-cut" would allow for judgements about where we are investing in this important area and where important questions might lie unanswered. The information provided by the NSF is an important step in that direction.

[ Contents ]

New Additions to the WWW Site

Emergency Management

[ Contents ]


[ Contents ]

El Niño

[ Contents ]

Tropical Cyclone

[ Contents ]

Economic & Casualty Data

[ Contents ]

[ map | home | feedback ]