A recent book about the assassination of President James A. Garfield describes the horrific medical treatment the wounded president received and the sad fact that his death was less a consequence of the assassin’s bullet than it was of the ignorance of his doctors.

It is a sobering lesson about the costs of ignorance, with relevance for today.

Garfield was a highly respected Ohio congressman elected president in 1880. His assassin was a drifter and swindler who believed a grateful nation would thank him for killing the president. He had been seeking appointment as consul to Paris, though he was as marginal and delusional a character as Lee Harvey Oswald, who killed a president 80 years later.

Garfield was shot in a railroad station in Washington, D.C., and the physicians who rushed to the scene immediately began probing the wound with their unwashed fingers. Two months later Garfield would be dead from the infections that had ravaged his body as a result of a lack of awareness of germs and the importance of sterilization.

Joseph Lister was the British surgeon who pioneered the theory of germs and the importance of sterilization in surgical practice. The book on Garfield, called “Destiny of the Republic: A Tale of Madness, Medicine and the Murder of a President” by Candice Millard, describes how Lister struggled to gain acceptance for his ideas. In 1881, however, the medical establishment in the United States scoffed at the idea that invisible germs were responsible for infections. Doctors relished the blood and gore of surgery and took few precautions to keep their instruments or their hands clean.

Even in the face of evidence to the contrary, doctors stubbornly clung to their traditional beliefs. Thus, the doctors treating Garfield watched helplessly as his robust frame wasted away and infection riddled his body. It is likely that 20 years later Garfield’s life could easily have been saved, according to Millard.

The lesson for today is one, not just for the scientific community, but for all of humanity. The evidence is in on the changing climate and the dire effects in store for the planet. Within the scientific community, scientists differ on the rate of likely change or the degree of risk facing us, but there is virtually no argument about the reality of climate change.

Special interests have been fostering ignorance about that reality, which has paralyzed the United States, which ought to be leading an international effort to curb the emission of carbon dioxide and other greenhouse gases. Ignorance is often defended pridefully — that was the case among Garfield’s doctors. Relinquishing long-held beliefs is not easy, and the politicians who have labeled climate change a hoax are not likely to trumpet their mistake.

Like the presence of germs, climate change is invisible. It is a long-term change that manifests itself only over time and can seem contradicted by singular weather patterns. But the opposite of ignorance is knowledge, and our climate scientists have amassed a wealth of knowledge about climate patterns and their effects.

When invisible causes are manifest in visible fashion, then the case is more easily sealed. Eventually, the success of Lister’s theories showed that he was right. The climate is providing its own evidence: July was the hottest month ever. The extreme weather that has been pummeling the globe — floods, drought, heat waves —has followed the scientists’ models. Changing habitats reflect the changing climate.

The Garfield case was the tragic consequence of medical practitioners who hadn’t awakened to the scientific truths about the world around them. The consequences of ignorance about climate change, and of the devious work of the special interests who foster that ignorance, will afflict more than one man. The scientists who have been providing the data and the theories about the climate have assumed a heroic role, like that of Joseph Lister. We can hope the world soon heeds their warnings.