The Sierra Club campaign against coal is motivated by a desire to reduce CO2 emissions to prevent global warming. But since global warming skepticism and global warming fatigue are widespread, the club has opted for a junk science approach to reach its goals. The club tells people that their babies will die, or at least get asthma, if coal plants continue to operate. Although the cause of asthma is not known, it is suspected that it is related to the high levels of cleanliness in advanced countries that denies children and their immune systems exposure to the dirt and filth found in primitive places. This is known as the hygiene hypothesis. The incidence of asthma is about 50 times higher in developed countries compared to rural Africa. For all the Sierra Club knows, coal plants may prevent asthma. Given the hygiene hypothesis, that seems plausible.
With junk science, it is easy to scare people. There are many things that are bad for us that are present at low levels in the environment — for example, mercury, lead, radiation, or tobacco smoke. The junk science approach to trace toxins is to claim that if a high level of the bad thing would cause X people to get sick, then a level 10,000 times smaller must cause 1/10,000 as many people to get sick. Given 300 million people in the country, this math can give you thousands of people getting sick from low levels of mercury, lead, radiation, or secondhand tobacco smoke. This approach is known as the linear no threshold hypothesis.
The Sierra Club and its ally, the Environmental Protection Agency, lean on the small emissions of mercury from burning coal to work up a calculation of deaths from coal. They minimize the fact that much of the mercury falling on the U.S. comes from China, volcanoes, or even from burning dead bodies with mercury-based fillings in their teeth. Mercury pollution becomes an excuse to get rid of coal. Arguing the science behind such claims often degenerates into a paper chase about statistics and what studies are good or bad. From the bureaucratic point of view, the linear no threshold hypothesis is wonderful because it means that problems are never solved and there is always a need for more bureaucratic activity.
Norman Rogers, “Sierra Club at the Metropolitan Club”, American Thinker, 2011-11-11