Saguaro National Park and Climate Change

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 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.”



  1. I like to explain to climate change skeptics the simple idea that you can’t dump millions of tons of carbons into the atmosphere without some consequences. Our job as scientists is to uncover what those consequences will be.

    1. I agree that the job of scientists is to uncover consequences. Can you cite some physical evidence regarding those consequences?

      1. google…”climate change evidence”…the first site is NASA’s. they’ve got enough charts and graphs to fill a big report…which you can also look at. And please don’t tell me that NASA is part of some leftist conspiracy.

      2. Ari,
        In the climate change debate, people often lose site of the distinction between the fact that climate is always changing and the possible causes of climate change. I checked out the NASA site you mentioned. Their first two articles were on atmospheric carbon dioxide content over the last 650,000 years and on sea level. See my two articles that show NASA is wrong:
        Al Gore’s Favorite Graph
        Sea Level Rising?

      3. NASA, the American Geophysical Union, the American Meteorological Society, and nearly..(no, not nearly) every other scientific organization around the world…are all wrong? The American Association of Petroleum Geologists even changed their statement in 2007. I don’t get it. Why wait to do something? Do you want to explain to future generations that we did nothing?
        PS- Why are my comments on the ESA deleted?

  2. Your article is much better and is a much more balanced coverage of the conference than was in the Star.

  3. I should state at the outset, that the UN did not set up the IPCC to find scientific evidence to support the insane theory of anthropogenic global warming, but to cherry pick evidence that supported the theory and to discard or discredit ant evidence or scientist that proved the opposite.
    The UN at its African Review, discussed imposing taxes as a means of wealth re-distribution to benefit Africa.  The first option was a Tobin Tax, a tax on trade, but according to their own published summary, opted for a tax on CO2 emissions, which would be easier to enforce.
    To that end we had all the scare stories and the faked science:  The Hockey Stick Graph, The Tree  Rings Graph and of course Al Gores infamous sci-fi/horror film, An Inconvenient Truth, a film designed to frighten people into believing that their had been a sudden and unprecedented surge in global temperatures, and every natural disaster happening around us, was our fault.  We were to blame for burning fossil fuels, that our 0.04% CO2 emissions, which is a rise 0f 0.001% over the last 150 years, was a recipe for global disaster.  A threat to the existence of mankind, indeed some lunatic claimed that CO2, without which no life-form can exist, was a threat to human existence.
    In his film, Al Gore used the 650,000 tear-old ice-cores to produce a graph showing that rising CO2 levels had always been followed by identical rises in global temperatures.
    Evidence indeed if it were true, but . . .
    In the British High Court, the makers of Al Gore’s, ‘An Inconvenient Truth’ were forced to concede that the opposite of Al Gore’s claim was true.   Over the last 650,000 years the ice-cores clearly show that rising global temperatures were followed 800 -2,000 years later by identical rises in the levels of CO2.
    The court concluded that Al Gore had ‘inadvertently reversed the science.’
    Rising global temperatures force the oceans to produce more CO2.
    That’s basic science to all but the IPCC,  the cap and Trade fraudsters, politicians, and the Greens.
    The only way to decrease CO2 levels is to drain the oceans and blot out the sun.

    1. I’m amazed at how certain conservatives are that dumping millions of tons of carbon into the atmosphere is not and will not have an effect on the atmosphere. It’s as if you all are the climate scientists. I thought conservative meant to be careful. Don’t you think it would be a good idea to curb emissions of carbon until we get a better idea of what is going on in the atmosphere? Scientists have really not been at this very long…and have come an incredibly long way. There are still many questions to be answered, but in the meantime, let’s be conservative and find a way to incentivize pollution reduction.

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