On Saturday, Oct. 2, 2010, the National Park Service hosted a symposium at the Arizona-Sonora Desert Museum which considered “How might climate change affect Saguaro National Park.”

The keynote speaker for the morning session was Dr. Jonathan Overpeck from the University of Arizona, a lead author for the IPCC, and one of the scientists mentioned peripherally in the “climategate” emails. He spent a few minutes addressing that.

Overpeck said that the southwest was “ground zero” for climate change. He showed a graph of global temperatures from 1880 to present. I’ve seen him use that graph before. This is a case of cherry-picking to enhance a point. He starts the graph just as the planet began to warm from the “little ice age” so yes, the apparent temperature rise can be depicted as dramatic, especially if one expands the vertical scale of the graph. If, however, he had begun the graph 1,000 years ago during the Medieval Warm Period, the recent rise would have been seen for what it is, just part of the natural cycles.

Overpeck predicted that as temperatures rise, the southwest would become drier because the jet-stream which brings us winter rains will move north and its storms will move north with it. (The summer rains will have little change because they are drawn from the south.) Perhaps that will happen, and the year 2010 is an anomaly with an unusually high winter rainfall. My rain gauge recorded twice as much rain this past winter as I got during the summer monsoon.

Overpeck repeated several times that he has high confidence that human carbon dioxide emissions are responsible for the global warming we are experiencing. In the Q&A after the talk, I asked him to cite some specific physical evidence that human carbon dioxide emissions have produced significant warming. During his answer he said that climate models work best when carbon dioxide is added in, but that’s not evidence. He also made what I thought was an extraordinary statement. He said that most climate scientists (of his group) believe that carbon dioxide is responsible for global warming “because they can’t think of anything else” that would cause such warming. That too, is not evidence. In other words, a lead author of the IPCC climate studies cannot cite any physical evidence that human carbon dioxide emissions have a significant effect on global temperature. Rather, it must be so because they think it so.

Three talks dealt with saguaro populations. These studies are conducted on specific, small plots within the National Park; some were established as long ago as 1935. Each plot is periodically visited and saguaros are counted and measured. The assumption is that these plots are representative of the population as a whole, however, each plot may represent only a micro-climate, not the whole, and may be subject to special local conditions. For instance, in one plot, pack rats were eating the saguaros. The saguaro population is cyclic and depends on, among other things, the amount of precipitation, the number and severity of days of frost, and the health of palo verde trees which act as nurse plants to young saguaros. Some plots showed increases in the number of saguaros while others showed decreases. The National Park Service performs a saguaro census every ten years. Among the plots they studied there was a general increase in saguaro population over the last ten years. For more information on the NPS monitoring program, see http://science.nature.nps.gov/im/. See more details from Tony Davis’ article in the Arizona Daily Star.

Dr. Donald Miles of Ohio State University reported on lizard populations. His study involved study plots similar to those in the saguaro studies. Since lizards are ectothermic, rising temperatures may limit their hunting time since the lizards cannot be outside if it is too hot. Miles reported that certain lizards have become “extinct” from some study plots and predicted that 66% of species will become extinct in 40 years. He did mention that his extinction models have not been calibrated with actual extinctions. When pressed during Q&A, Miles admitted that the “extinction” really meant that the lizards were not observed in the test plots and that they simply could have moved to better climes.

Dr. Phil Rosen studied reptiles along transects in Organ Pipe National Monument. He found no significant lizard decline, but did find decreased populations of snakes (except for sidewinders).

Kris Ratzlaff, a University of Arizona graduate student, studied lowland leopard frogs and canyon tree frogs in the Rincon Mountains. Her study provides baseline data for future investigations. She found that almost all leopard frogs in the three drainages studied were infected with the chytrid fungus, a problem for frogs world-wide. There was much less infection among the tree frogs.

Dr. Travis Huxman gave the keynote talk of the afternoon session. Huxman is a University of Arizona biology professor and director of Biosphere 2. He noted that rising atmospheric carbon dioxide makes plants more productive and more drought tolerant. The magnitude of this aerial fertilization effect is tempered by the type of plant (fast growing vs. slow growing) and by the amount of water available.

Much of the symposium was about speculative problems. There is, however, one real and current problem that has little to do with climate change: the invasion of exotic grasses such as buffelgrass.

Native grasses are generally confined to higher elevations and cannot survive on the hot desert floor. However, non-native species imported for cattle feed, highway beautification, and landscaping, can survive on the desert floor, and that is the problem. “Buffelgrass grows densely and crowds out native plants of similar size. Competition for water can weaken and kill larger desert plants. Dense roots and ground shading prevent germination of seeds. It appears that buffelgrass can kill most native plants by these means alone.” The other problem is that these exotic grasses fill in the space between native plants and thereby can transmit wild fires.

The take-away from this symposium is that the issues are complex. While we would all like some definitive answers, real science is messy.

For more information on droughts, see my article “Drought in the West.”