My emotional response to “The Wipeout Gene,” in which Bijal P. Trivedi describes the use of genetic modification to destroy the mosquito species Aedes aegypti, was trepidation. We see A. aegypti as the vector of human diseases, but the global ecological significance of the species is unknown.

Also disturbing is the implication that assent obtained during a town hall or village meeting of lay individuals was mean­ingful when substantive understanding of arthropod gene manipulation and its ecological impact is limited among scientists.

It is arrogant, reckless and hazardous to make value judgments on the significance of a species.
Charles F. Lovell, Jr.
Past member, National Vaccine Advisory Committee

In addressing future food supplies and environmental degradation, Jonathan A. Foley’s “Can We Feed the World and Sustain the Planet?” doesn’t mention the elephant in the room: agricultural output has dramatically increased but so has population.

Until the countries that can help provide the means, at affordable prices, to enable people to control their family sizes as many want to do but can’t, humanity is chasing its tail.
Les G. Thompson
Victoria, Australia

Foley could have missed a viable answer to world hunger that would also help mitigate climate change: insects as human and other animal food. Most insects produce very little methane for high-quality protein.

The United Nations Food and Agriculture Organization is mounting an effort to address insects as human food and is planning a world conference for 2013. Academics who refuse to think out of the box and address entomophagy as a valid partial answer to world hunger ignore a useful, productive and highly nutritious solution.
Robert Eller Diggs
Bozeman, Mont.

Foley’s article overlooked food from the sea. Properly designed fish farms can provide a healthy and plentiful supply of food by using our natural resources more efficiently.
Albert Rettig
Tel Aviv, Israel

In “Digging Mars,” Peter H. Smith’s overview of the science of exploring the Red Planet, the evidence seems to indicate significant variation in the Martian climate. Earth also has wide swings in climate that are thought to be caused by variations in its orbit. Serbian geophysicist Milutin Milan­kovic´ identified three of these: orbit eccentricity, axial precession and tilt. Has Smith considered whether or not Mars also has these so-called Milankovitch cycles?
Jerry L. Lundry
Bellevue, Wash.

In discussing the Phoenix mission, Smith indicates the spacecraft traveled 600 million kilometers to Mars and estimates “the light travel time to Earth” as “about 15 minutes.” But at 186,00 miles per second (about 18 million kilometers per minute), light would need about 33 minutes to make the trip from Mars to Earth.
Roger Rubens
Boynton Beach, Fla.

SMITH REPLIES: Regarding Lundry’s ques­tion, Milankovitch cycles influence the climate on Mars even more than on Earth. Not only does the axis precess (every 51,000 years), but the proximity of Jupiter offers a strong gravitational forcing function that modifies the eccentricity of its orbit and the obliquity (tilt) of the spin axis. As the obliquity wanders with large, chaotic variations (cycles can be several million years), the climate is strongly affected to the point where, during large tilts, the polar ice caps can migrate toward the equator, forming large glaciers on the tall volcanoes.

To clarify Phoenix’s light travel time: the spacecraft did not cruise straight to Mars but took a longer path following an elliptical orbit around the sun, with Mars at the aphelion. Because the distance from Mars to Earth was about 250 million kilometers during the mission, the one-way light travel time was a little less than 15 minutes.

Thought Experiments,” by Joshua Knobe, describes the question of free will versus determinism. I think it’s impossible to determine (pun intended) whether we live in a deterministic or free-will world.

I believe I have free will. But suppose I’m wrong. Then it’s determined that I will believe that I have free will. We can conduct the experiments that Knobe talks about, but doing so assumes free will. Otherwise, the outcomes are determined.
Ted Grinthal
Berkeley Heights, N.J.

There is another way of thinking about morality than the one put forward by Knobe. Instead of it being essentially altruistic, noble and somehow emanating from inside us, we can think of it as focused largely on how we want others to behave toward us.

If others behave morally, they create an environment that is generally beneficial to us. Our own “moral” behavior, however, is dependent on whether there are effective social sanctions that make it advantageous to behave in a particular way. From this perspective, it is easy to understand the relatively constrained behavior of people who are part of a religious or other mainstream group and the more fluid “morality” of those who are “open to experience.”
Peter Rowbotham
West Vancouver, B.C.

In “A Formula for Economic Calamity,” by David H. Freedman, David Colander of Middlebury College asserts that climate models often have no terms to account for the effects of clouds. This is not true. In my class on climate change problem solving, I use a 2005 paper by M. H. Zhang et al. that compares modeled clouds with observed ones from 10 climate models. There are many earlier and later references that document over three decades of ever more sophisticated inclusion of clouds in weather and climate models.

The statement that clouds are not included is misinformation that has been propagated in political arguments used to discredit such models. There is an important difference between physical climate models and economic ones: namely, physics. The physics of climate change are simple classical physics in a stunningly complex, multiscale system, so it is possible to design experiments based on cause and effect. The uncertainty associated with future climate projections linked to economic possibilities of what people will do is far larger than the uncertainty associated with physical climate models.
Richard B. Rood
Department of Atmospheric, Oceanic and Space Sciences
University of Michigan

FREEDMAN REPLIES: Rood is right to point out that climate models are often designed to try to account for clouds. The statement in the article, which was attributed to an economist and not a climate scientist, was a vague oversimplification that suggested climate models frequently fail to account for clouds. In fact, the climate science literature is replete with papers that call out the challenges of accurately accounting for clouds in models. Surely if we have to err in gauging uncertainty in science, it’s better to err on the side of overestimating it. If only economists working in financial risk models had done just that.