Solar Plants May Make Deserts Too Hot For Tortoises

We've paid plenty of attention here at KCET to the problems caused for desert tortoises when their habitat is replaced with renewable energy facilities. But now one scientist is saying that big solar facilities in the Mojave could seal the desert tortoise's fate in a way you might not expect.

According to Barry Sinervo, an evolutionary biologist at the University of California Santa Cruz, current solar projects in the California desert intended to slow global warming, including two approved just last week by the Interior Department, could actually make the desert too hot for tortoises to survive past the end of the century.

In fact, suggests Sinervo, solar projects' effect on desert climates may speed the extinction of desert tortoises by as much as 50 years.

The desert tortoise, Gopherus agassizi, is a federally listed Threatened species.

Sinervo's comments came in the form of a presentation at the Annual Meeting And Symposium of the Desert Tortoise Council, held in Ontario, California the weekend of February 21-23. An abstract of Sinervo's presentation, along with others made over the weekend, is available online. Sinervo's presentation modeled the likely effects of climate change on the tortoise, and concluded that if humankind embarks on reasonable measures to lower its emissions of carbon dioxide into the atmosphere along the lines of the IPCC's "B Scenarios" (described briefly here,) then desert tortoises might still be able to hang on in two important habitat areas in the California desert as late as 2080, giving the species a shot to survive into the next century.

The bad news is that both those areas -- California City and the Ivanpah Valley -- are targeted for intensive solar development. In a particularly timely example, the U.S. Department of the Interior just last week approved several thousand acres of new photovoltaic arrays for the Ivanpah Valley. Projects like those, say Sinervo, could deprive the tortoise of its last best chance for survival by making the reptile's potential refuges too warm.

At issue is the so-called "urban heat island" effect, in which human-made structures that absorb solar energy can significantly raise nearby temperatures. The effect holds true even when the setting isn't urban, as is the case with large remote desert solar installations. After all, the purpose of solar panels is to absorb as much solar energy as they can. About a fifth of that energy is turned into electricity under optimum conditions: the rest is released into the surrounding environment as heat.

According to Sinervo's abstract, the heat island effect of large solar arrays can raise ambient temperatures by between .4° and .75° Celsius, which works out to one degree Fahrenheit give or take a quarter degree. Given the amount of warming already locked in for the deserts by 2080, well before even the most aggressive likely climate change programs will start to affect global temperatures, that extra degree or so of warming will likely be enough to do in the tortoise.

As Sinervo says,

About 95 prcent of the desert tortoise and its close relative the Sonoran desert tortoise, Gopherus morafkai, are expected to die out due to climate change and other factors by the end of the century even in best-case scenarios. That makes it all the more important that we limit our emissions of greenhouse gases.

But Sinervo's abstract makes it clear that it matters to the tortoise how we tackle that task:

Founded in 1976, the Desert Tortoise Council is a non-profit scientific organization dedicated to promoting conservation of North American desert tortoises.