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Natural Climate Variability on Decade-to-Century Time Scales
Temperature change as a function of time interval in various bioclimates. It is the time during which temperature at the particular location was increasing. Data sources: Brooks, 1958; Geiger, 1965; Hare and Hay, 1974; Koeppe and De Long, 1958; Landsberg, 1958; Yoshino, 1975.
climatic trends. So it is of interest to see how microclimate (and mesoclimate) varies over space.
Figure 5 presents data from a number of sources on the variations in temperature that may be found within distances ranging from a meter or so to one kilometer. Most of these are for maximum daytime temperatures, and have been chosen to illustrate typical conditions.
Large differences in temperature—on the order of 10°C to 15°C—can be found in close proximity, as on the sunny side of a small mound or furrow as compared with the opposite side. Significant but less extreme temperature differences can be found over distances ranging upwards of 10 meters. Microclimatic extremes are greater than mesoclimatic extremes. Indeed, a negative exponential decrease in the temperature differences as a function of distance between measurement locations appears in this sample.
It seems to me that this considerable variability has significance for predictions of ecological change in response to "global warming". Any long-term increase (or decrease) in the temperature to which a plant or ecosystem is exposed will have some effect. Plants in specific locations within an ecosystem may not be able to survive. But plants at unfavorable boundaries in the same ecosystem may reproduce in more favorable conditions nearby; their geographical range may thus be altered. Whether this is a "catastrophic" response depends on human definitions.9
Science (1988, 242:1010) asks, "Is there life after climate change?" and answers "Yes, but the world will be a different place, with an abundance of male alligators, migrating trees, and a plethora of parasites." It is absurd to ask what will happen after climate change; climate is changing all the time, at all possible scales of time and space. There is no before and after. Thompson Webb is quoted in this article as saying that we are moving into a new biological world. In actuality, we are forever moving into new biological worlds. The relevant question for public policy is whether the climatic changes that occur as the result of increases in greenhouse gases will have consequences that are obviously and dramatically disruptive of ecosystem behavior and human response.
We might ask ourselves whether, if we had never heard about "global warming," would we have inferred that such a process was at work, on the basis of observations of plant and animal behavior (or even the climatic record) during the past century. I contend that we could not. Long-term climatic change—from whatever cause—is masked by the