A smartphone links patients' bodies and doctors' computers, which in turn are connected to the Internet, which in turn is connected to any smartphone anywhere. The new devices could put the management of an individual's internal organs in the hands of every hacker, online scammer, and digital vandal on Earth.

Smartphones can relay patients' data to hospital computers in a continuous stream. Doctors can alter treatment regimens remotely, instead of making patients come in for a visit.

A world with a sudden limit on air travel would be tremendously different from the one we live in now.

The legal fight over climate change begins in the United States with the Clean Air Act Amendments of 1977. Under the Act, the E.P.A. is required to publish a list of 'stationary sources' of air pollution, of which the most important are power plants.

As an issue, climate change was unlucky: when nonspecialists first became aware of it in the 1990s, environmental attitudes had already become tribal political markers.

By the 1980s, businesses had realized that environmental issues had a price tag. Increasingly, they balked. Reflexively, the anticorporate Left pivoted; Earth Day, erstwhile snow job, became an opportunity to denounce capitalist greed.