A growing number of experts say it is time for a broad discussion of environmental effects of emerging geoengineering projects.

Examples of such projects include “fertilizing” parts of the ocean with iron, in hopes of encouraging carbon-absorbing blooms of plankton; and injecting chemicals into the atmosphere, launching sun-reflecting mirrors into stationary orbit above the earth, or taking other steps to reset the thermostat of a warming planet.

Similar questions are being raised about nanotechnology, robotics and other powerful emerging technologies.