Rachel Carson, who spent many summers on Southport Island, Maine writing about marine life as a scientist and naturalist, was not a biochemist. However, after publishing The Sea Around Us, which won the National Book Award in 1953 and two other books in her ocean trilogy, Under Sea Wind and The Edge of the Sea, she published Silent Spring in 1962, a book about biochemistry that changed the world. Silent Spring, which spawned the modern environmental movement in America detailed the links between the use of DDT and the alarming health effects on birds and humans.

After its publication, Carson was immediately attacked by the chemical industry that ridiculed her training in marine biology, as well as her personal life as an unmarried woman without serious credentials. The former Secretary of Agriculture, Ezra Taft Benson, wrote president Eisenhower that because Rachel Carson was unmarried, but physically attractive, she was “probably a Communist.” Leading the attack on Carson’s book was a biochemist, Robert White-Stevens from American Cyanamid, a major chemical manufacturer who derided her a “fanatic” and suggested that if the country were to follow her advice about cutting back the use of pesticides “we would return to the Dark Ages and the insects and diseases and vermin would once again inherit the earth.” But when they both appeared on CBS’ influential program, CBS Reports, White-Stevens came across as loud and shrill, undermining his attempt to portray her as a fanatic.

The chemical industry lost the public relations battle badly as the U.S. government quickly agreed to ban DDT to address the concerns that Carson had raised.

Two years after the publication of Silent Spring the U.S. Surgeon General’s office first issued its 1964 finding of a causal link between cigarette smoking and lung cancer in men. But it was not until 31 years later that President Clinton announced plans in 1995 to have the Food and Drug Administration regulate the sale of cigarettes, especially to minors. In the intervening 30 years, the tobacco industry realized that they did not have to disprove a link between smoking and lung cancer, all they had to do was to try to undercut the findings of scientists whose studies had found such a link. By sowing enough doubt on the science behind the serious health effects of tobacco, the hugely profitable and politically influential tobacco industry was able to avoid regulation for over three decades. Despite overwhelming scientific evidence to the contrary, not to mention common sense, a well-orchestrated campaign of doubt was a startlingly effective strategy for an industry few could love.

In 1988, another government scientist, James Hansen, head of NASA’s Goddard Institute of Space Studies, became one of the earliest scientific voices to declare with “99 percent confidence that the Earth was being affected by human-made greenhouse gases and the planet had entered a period of long term warming.” Hansen warned that, “global warming increases the intensity of drought and heat waves and the area of forest fires.” And because a warmer atmosphere holds more water vapor, Hansen said we should also expect heavier rains, more extreme floods, and more intense storms such as thunderstorms, tornadoes and tropical hurricanes and cyclones.

Since 1988, a well financed campaign, primarily funded by corporations with large fossil fuel holdings have tried to sow doubt either on the existence global warming itself (“it is just natural variability”) or on the evidence that burning of fossil fuels by humans is the cause of climate change. It is not hard to find scientists who, when asked about whether the climate is changing as a result of the build up of carbon dioxide in the atmosphere, will honestly say, “We just don’t know.” There are more venal actors as well, including some in academia where contrarian views can be a badge of honor, who will say that most climate change science is based on a high degree of uncertainty or will introduce other non-human causes to explain the observe changes in climate.

The merchants of doubt understand human psychology all too well. If your mind is balanced between yes and no; between acceptance and denial; between this possibility and that possibility—the longer you are in doubt, the less action you take. Action means that you have decided something. So if someone can convince you that we do not have enough information on which to base a decision, inaction is the inevitable result. And if you have an economic interest in preventing action, doubt is your most effective tool, particularly because doubt can seem so reasonable. Even when it is not.

Meanwhile, record temperatures, record numbers of freak storms, record numbers of forest fires, and record numbers of counties in drought keep piling in. Recently, the National Oceanic and Atmospheric Administration reported that the winter and spring throughout the Northern Hemisphere, Europe and northern Africa, where most land is situated, experienced much higher average monthly temperature records. Only northern and western Europe and the northwestern U.S. were cooler than normal. Corn futures have sky rocketed as drought grips vast swaths of the nation. Food prices will rise. More people will be hungry.

The consequences of planetary climate change are beyond the scariest predictions of Rachel Carson’s silent spring and even more dispiriting than the millions of deaths caused by tobacco companies’ efforts to obscure the link between cancer and cigarette smoking. A warmer average world climate by a mere two degrees will impose catastrophic costs on billions of people and hundreds of governments across the planet. We have already warmed the planet by about 1.3 C in the past hundred years and the rate of warming is rapidly increasing. The next time someone tries to convince you the science of climate change is uncertain, use your own senses—your eyes, nose and skin—and act on your own common sense.

Philip Conkling is president and founder of the Island Institute based in Rockland, Maine.