by Whit Gibbons

April 6, 2008

I gave a talk about global warming or, if you prefer, climate change to a group of very well educated high school students, not all of whom were in agreement about some aspects of the topic. I said that I realized some people did not fully believe that the earth's climate was changing and that temperatures were rising. But the data and its interpretations from myriad scientific sources have convinced me that global temperatures have risen measurably during the last century. My position was that they should probably accept that as fact.

I noted that the earth's temperature has changed dramatically over the last 20,000, not to mention the last million, years as witnessed by the confirmed ice ages and the intervals between them. Such change can be normal. During an ice age, much of the world's water is captured in glaciers and enormous continental ice fields. The ocean level falls during such periods because so much of the world's water is tied up in ice. During the interglacial periods, when the earth warms up, the ice melts and the oceans rise. The earth is behaving now as if it were in an interglacial period, with rising temperatures. To appreciate the dramatic changes that can occur, consider that at one time or another over the last few thousand centuries, the sea covered the land up to Columbia, South Carolina; Augusta, Georgia; and Tuscaloosa, Alabama. Kind of sobering to think of that happening again.

The politically charged part of global climate change is whether current conditions are caused by humans, namely the powerful industrial countries like the United States. Also in contention is what our personal and national responsibilities are even if we are implicated as the cause of global warming. That debate in a high school class, or anywhere, could go on for the rest of the semester, so I turned to another level of the global warming issue. How will animals respond if temperatures are indeed on an upward trend?

I selected reptiles and amphibians as examples of how certain wildlife could be affected by global warming, and I brought a snapping turtle, box turtle, and alligator as the poster children to demonstrate how temperature can affect sex ratio. In many species of turtles the sex of the baby is determined by the temperature at which the egg is incubated. A variety of environmental factors are involved, but in simplest terms, when turtle eggs are raised at warm temperatures they produce female babies. Cooler temperatures produce males. Alligators are more complex in that temperatures around 90 degrees F produce males, but higher and lower temperatures produce females. If environmental temperatures were raised significantly, only one sex of some species would be produced. The inexorable trajectory would be extinction.

I also indicated that a major impact of global warming would be on species that rely on seasonal patterns of rainfall and temperature for reproduction. I used some of the colorful southeastern salamanders as examples. Marble salamanders breed in the fall, when it rains. Tiger salamanders breed in the winter, when it rains. If the seasonal rain patterns shift and certain regions go from fall to spring, with no winter, what will happen to such species? What will be the effects on aquatic species if droughts become severer and more prolonged? Finally, the environmental cascade effect could be a far-reaching impact of global warming. Even though some species might be able to adjust to rising environmental temperatures they would be affected because their food sources are not so adaptable. A predator's livelihood depends on its prey. If the prey species declines in numbers so will the predator.

The most gratifying part of my talk was not whether I convinced the students that global warming is real and will have consequences. More important was seeing how dedicated teachers can encourage bright high school students to discuss controversial environmental issues in class. The true education comes from their addressing the issue from a variety of perspectives, hearing different viewpoints, and learning to base decisions on science and facts rather than politics and talk-radio rhetoric.

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