NASA’s PACE satellite will tackle the largest uncertainty in climate science

Small things can have big effects. Take the plant plankton that populate the Earth’s oceans. When zooplankton eat them, the phytoplankton release a chemical called dimethyl sulphide (DMS) and it is this that people are referring to when they speak of the “smell of the sea”. Chemical reactions in the atmosphere turn DMS into sulphur-containing particles that offer a surface for water vapour to condense on. Do that enough times and the result is a cloud. Clouds, in turn, affect both the local weather and, by reflecting sunlight into space, the world’s climate.

Other tiny things have similarly extensive effects. Sulphur from ships’ funnels also makes particles that seed clouds, producing strings of puffy white “shiptracks” that can be seen in satellite pictures. Soot from burning fossil fuels, meanwhile, has the opposite effect. It is made of dark particles that absorb solar energy, warming the air around them and discouraging cloud formation. If sulphur particles make it high enough in the atmosphere (thanks to a volcanic eruption, perhaps) they can form a haze that blocks some sunlight from reaching Earth’s surface.