Michael Poellot

Dept. of Atmospheric Sciences University of North Dakota Grand Forks1 ND 58201

WEATHER WEIRDNESS

It's beginning to sound like a catastrophe of nearly Biblical proportions or the plot of a Hollywood disaster film. Devil's Lake water level reaches a record high. Hurricane watchers nearly run through the alphabet in named Atlantic tropical storms and hurricanes. A drought in South America wipes out crops and livestock. Record floods and storms devastate Europe. Record floods strike the Midwestern states. More droughts, floods, typhoons, record heat and cold -- has

ÏMother NatureÓ gone wild? What has happened to our weather? Questions like these are being asked more frequently as we are presented with a growing list of natural disasters. It is not uncommon to find in the news media some sort of weekly environmental report highlighting the World's Worst Weather for the Week.

In fact, those whose livelihood is at the mercy of the weather don't even have to watch the news to find out that the weather is not behaving as it should, or at least how we would like it to. There are few, if any, industries that are any more affected by the weather than agriculture or are more vulnerable to its extremes. This is particularly frustrating in view of the tremendous technological advances being made in almost all facets of ag production. However, in the final analysis, varying combinations of temperature and moisture can lead to favorable growing conditions and bumper crop yields one year, and plant stress, insects, disease, and sharply reduced yields the next. Thus, agricultural producers have a vested interest in how the weather behaves and what change's might be in store for the future.

It is my intent in this presentation to address the question ÏIs something wrong with our weather?" I don't think I will be able to provides an answer that is satisfactory to everyone. However, I do' hope to provide you with some information concerning some of the issues associated with our weather and how it might be changing.

WHAT EVER HAPPENED TO NORMAL WEATHER?

Before we look at what is happening to our "weather", we first need to define the problem. The term "weather" is used to describe the state of the atmosphere at a certain point in time. Thus we talk about how cold the weather is today, how hot it was last June, and wonder what it will be like for planting this spring. A measure of atmospheric conditions that is perhaps even more important is what is called "climate." This term is used to describe the longer-term averages of our daily weather. It is the climate of a location that determines the ultimate form and success of agricultural operations in that area. As such, this presentation will focus more on possible changes in climate rather than what the weather will be this coming summer.

The big question then is: are we undergoing a change in climate? One thing we do know about weather is that it is highly variable. All ag producers are aware, for example, that over a course of years it is common to have some wet cycles and some dry cycles, some spring seasons that are warm and others that are cool, and so OIL Figure 1 shows the annual mean temperature of the United States from 1895 to 1991. Two features of this graph are worth noting. First, there have been frequent wide swings in mean temperature from cold to warm and back over this time period. Second, the average temperature hasn't really changed a whole lot, although it does seem to be trending upward in recent years (more on this later). These fluctuations in temperature are what is called "natural variability". That is, variations in climatic conditions occur due to such factors as volcanic activity, slight changes in the output of the sun's energy, and complex interactions between the atmosphere and the oceans like the El Nino/Southern Oscillation. This natural variability is a critical problem in the climatic change issue because it masks possible longer term trends.Figure 1. Variation in annual mean temperature of the United States for 1895-1991. Horizontal line is the mean for the period. The smoothed curve shows the trend. From Meteorology.

It is the long term record of such fluctuations in temperatures and precipitation that have been used to compute what are called "normal" values for a given place and time. These average numbers are valuable for some applications. For example, they are used in determining parameters such as growing degree days for input into crop models and predictions of crop growth and yield. However1 they are often over-used in describing recent or forecast weather conditions: "The high temperature tomorrow will be 10 degrees below normal," or "June was wetter than normal by .34 inches." It is important to remember that "normal" values are just averages of conditions that have been observed over a period of years, and that it is perfectly normal for conditions to be different than these averages. In fact, it would be very abnormal to have a string of even three or four days with exactly average high and low temperatures and precipitation. Figure 2 shows an example of daily temperature variations and normal values.

Grand Forks Temperatures for 1993Figure 2. 1993 Daily temperatures, normals and records for Grand Forks

It is also important to realize that the history of reliable weather records in many locations is not very long. For example, for a station with a 100-year period of records, a "record" high temperature for a certain day means it had never been that warm during the past 100 years. However, it may have been even warmer some year not long before that. From a practical standpoint, though, we tend to think of normal in terms of what we remember past weather to be like. Perhaps, then, the recent apparent change in climate is not real, it is only perceived.

Certainly the public awareness of weather extremes has been heightened in recent years by extensive news coverage and well-publicized research efforts. Worst-case scenarios presented by groups pushing for regulatory action and other genuinely concerned individuals often attract a lot of media attention. We have also been brought closer to formerly distant countries through new communications technologies, increased air travel, radical political changes and increased trade. This has created a much tighter and more interdependent global community. Finally, societies have also become more susceptible to the natural weather extremes as a result of an increasing world population, marginal cropping and grazing practices, and inappropriate land use patterns. All of these factors could lead us to believe that our climate is changing when it really isn't.

WHAT ABOUT GLOBAL WARMING?

On the other hand, scientific research indicates that a climatic change is actually taking place. As mentioned earlier with reference to Figure 1, there is growing evidence that the earth's climate is undergoing some warming. We have already seen that the natural year-to-year variability in weather is making it difficult to determine whether or not this warming is actually occurring and if so, how fast. There is other evidence beyond just temperature records, however, that also points to warming. This includes the retreat of many glaciers and a gradual rise in the mean sea level. If the earth's atmosphere is indeed getting warmer, what could be the cause?

The most likely source of global warming is due to an increase in the amount of carbon dioxide (C03), methane and other trace gases in the atmosphere. While trace gases comprise only a small fraction of the atmosphere, they play a large role in regulating the temperature at the earth's surface. They do so by absorbing a portion of the infrared or "terrestrial" radiation (heat energy) given off by the earth which would otherwise escape into surface. - Some of this heat energy is then re-radiated back to earth, helping to keep us warm. This is what is called the greenhouse effect". Without the presence of these greenhouse gases in our atmosphere, the temperatures on earth would be more like those on the moon. There is concern about increasing levels of these gases in the atmosphere because this would result in the absorption of more terrestrial radiation and, consequently, rising temperatures.

There has been a steady increase in CO2 concentrations since the beginning of the industrial revolution and this has been linked to the increased burning of fossil fuels. Measurements of concentrations of CO2 dating back thousands of years have been obtained by analyzing ice core samples from Greenland; more recent values have been measured in several remote locations (see Figure 3). Even though large quantities of CO2 are removed by plants through photosynthesis and also dissolved in sea water, there has been enough excess production to cause a potentially sign)ficant increase. Greater amounts of methane have been detected and linked to various agricultural activities. Industrial emissions have also added sign)ficant amounts of other greenhouse gases to the atmosphere.

Figure 3. Measurements of the CO2 concentration at Mauna Loa, Hawaii.

Other human activities may also be causing climatic changes, particularly on local or regional scales. One of these changes is a decrease in the amount of ozone in the lower stratosphere caused by the release of man_made chlorofluorocarbons (CFCs) from aerosol cans and refrigerants. While this decrease will not lead to an appreciable rise or fall in surface temperatures, it is allowing greater amounts of ultraviolet radiation to reach the earth's surface. This could lead to increases in skin cancer and also harm crops and other vegetation. Climatic changes are also likely being caused in some areas of the world by activities such as deforestation and overgrazing.

THE FUTURE

If the earth's climate is changing, what does this mean for society in general and the agindustry in particular? There are a number of factors that will determine what the ultimate impact of this change is. One is how much warming will eventually take place. So far, it appears that there has been only a few tenths of a degree increase. Perhaps more importantly, what changes in precipitation patterns (amount, timing, intensity) will accompany the warming. A third concern is how quickly the change will take place. A rapid shift would be much more difficult to adjust to than a gradual one. Another key factor will be how the climatic changes are distributed around the globe. Some regions may be much more affected than others. Finally, a key factor for ag producers will be whether or not the global warming is accompanied by an increase in the frequency of extreme weather events such as droughts and floods.

The potential impacts of climatic change on agriculture are enormous. For a given region, these could mean changes in cropping types and patterns, and perhaps even a total loss of sustainability. Profitability could be greatly affected. New crop varieties may be needed. The global market could become even more important.

What is the most likely scenario for global climatic change? Making such a prediction is a daunting task given the complexity of the earth_atmosphere system. One approach to the problem is to study previous climatic conditions on earth through examination of various types of physical evidence such as ice core samples, tree rings, ocean sediment and other geologic data. From these data, scientists have been able to estimate climate history for the past 200 million years or so. They are now using this information to estimate how our climate may change in the next 100 years. There are, of course, limits to the usefulness of this approach because future changes might occur at a different rate or in a different manner than those of the past.

A second way of looking into the future is through the use of computer models of the earth's climate. These models use the fundamental laws of nature which describe how the atmosphere works. The model is given a set of initial conditions and, based on a number of assumptions, climatic conditions at time steps into the future are calculated. Such models are very useful in that they are capable of showing possible regional effects of climatic change. They can also be run repeatedly for varying assumptions about factors like CO2 concentrations in order to see how sensitive the climate is to these factors. These computer models have definite limitations, however, because atmospheric processes cannot be represented with 100% accuracy, nor are present_day computers powerful enough to resolve with sufficient detail. In addition there are still many processes and relationships we do not fully understand.

IS SOMETHING WRONG WITH OUR WEATHER?

As is often the case when studying a problem research into climatic change has raised almost as many questions as answers. It does appear as though the earth's climate is getting warmer and will continue to do so, on average, for some years to come. The details of how this will take place and what effects it will have on agriculture are not known at this time. It is tempting to attribute any and all extreme weather events to global warming and to conclude that doom is impending. It is not clear, however, that the current weather events are anything more than natural variability.

Climate predictions are still tentative and for the time being will have little impact on the routine decisions: Will I be able to spray tomorrow? Can I let the crop stand and dry down a few more days? What should I plant this spring? Fortunately, progress is being made toward the goal of providing more accurate and timely short and long-range forecasts and seasonal outlooks.

REFERENCES

Prospects for Future Climate. Edited by Michael MacCracken, Mikhail Budyko, Alan Hecht and Yuri Izrael, Lcwis Publishers, Inc., 1990.

Meteorology. Joseph Moran and Michael Morgan, Macmillan College Publishing Co., 1994.

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