Smoke and steam billow from cooling towers and smokestacks at the Bruce Mansfield power plant near Shippingport, Pa. (Joby Warrick/The Washington Post)

I largely agreed with Maria T. Zuber’s reminder that we can do more for workers and communities whose livelihoods depend on a rapidly dwindling use of coal for producing power [“Wage war on coal emissions, not coal country,” op-ed, Feb. 26]. But one short segment of her essay should be challenged. Zuber wrote that climate change will impose “devastating risks on current and future generations. There is no escaping these facts, just as there is no escaping gravity.”

Gravity is fundamental and indisputable. Future risks of climate change are just now coming into focus. Our knowledge of these risks is based on hundreds of assumptions built into complex models — assumptions that are changeable, challengeable and, in some cases, somewhat speculative. Comparing climate models to gravity seriously overstates our degree of understanding. Whether the risks involved are manageable, serious or, as Zuber maintained, “devastating” is an important value judgment, but one that is a matter of policy and largely outside the realm of science itself. 

Climate scientists need to be more careful than most not to conflate scientific facts with personal opinions about public policy. Though I am a firm believer in the seriousness of human-caused climate change, I wish Zuber had been more careful about keeping scientific certainties (gravity) distinct from useful but imperfect models (climate-change risk) and had better distinguished fact from opinion. 

David Sarokin, Washington

In her op-ed on coal country, Maria T. Zuber wrote that “when coal burns, it emits more carbon dioxide than any other fossil fuel.” By itself, this statement is meaningless. Did the author mean more carbon dioxide per kilogram of coal? Per kilogram of carbon? Of hydrocarbon content?

Compounds that include hydrogen and carbon burn in air — they release heat when combining with oxygen. The amount of heat released is the difference between the energy (heat) released when the hydrogen-carbon bonds and the molecular oxygen bond are broken, releasing heat, and the carbon-oxygen bonds of carbon dioxide and the hydrogen-oxygen bonds of water are formed, absorbing heat. In the case of coal, oxidation of the impurities in coal also absorbs heat, forming ash. The heat produced depends on the amount of hydrocarbon burned and thus also on the type of coal (anthracite, bituminous, etc.) burned. Natural gas is almost pure hydrocarbon (mostly methane).

Ruth Weiner, Washington

The writer is a former chairman of
the department of physical sciences at Florida International University.