Successful policymaking must take into account people’s feelings, he believed. When Professor Juma helped design a stove for use in developing countries, its metallic cylinder was replaced with a clay lining to improve efficiency. But the prototype caused less smoke — attracting more mosquitoes — and villagers worried that metal workers could lose their jobs. A later model used metal and clay.

“Ultimately, all development is experimental; no one knows what they are doing,” Professor Juma said with a laugh in 2014. “Africans need the chance to experiment as well. They will make mistakes, but they can learn from them, too.”

Professor Juma could be lighthearted in the classroom or in public in order to make his points. With more than 100,000 followers on Twitter, he shared with them cartoons that teased skeptics of science and innovation. One of his last posts featured a game show called “Facts Don’t Matter.” In it, a contestant is told: “I’m sorry, Jeannie, your answer was correct, but Kevin shouted his incorrect answer over yours, so he gets the points.”

“Calestous was very serious about getting his work right, but he was not serious about himself,” Mr. Elmendorf said. “He shared his enjoyment of the research and teaching, though he was working on life-or-death issues for many people. He was incredibly optimistic.”

Professor Juma was born to John Kwada Juma and Clementina Nabwire Juma in the village of Busia, in western Kenya, on June 9, 1953. He grew up nearby in Port Victoria.

“Port Victoria was as remote as it gets — a small fishing village on Lake Victoria at Kenya’s westernmost point,” said Ken Kobe, who taught Professor Juma while serving as a Peace Corps volunteer there in 1969-70.

After graduating from Egoji Teachers’ Training College in central Kenya in 1974, Professor Juma became a science teacher in Mombasa, a port city on the Indian Ocean. He went on to write so many letters to the editor of the Nairobi-based newspaper The Daily Nation that it hired him in 1978 to be its first full-time science and environment correspondent.