On a Tuesday in August, Luke Iseman drove two hours east of Oakland in drought-stricken California to a remote spot where he launched a handful of balloons filled with sulphur dioxide and helium high into the sky.
From there, he used GPS to try to track the balloons as they rose into the stratosphere, the layer of Earth’s atmosphere that begins about 12km high and contains the ozone layer that protects the planet from solar radiation. Once there, they would burst and release the gas.