Nasa has enlisted the help of smartphone users around the world to monitor the effect of clouds on the Earth's climate. Information collected by users of the CloudSpotter app - where people take pictures of clouds and try to identify their type - will be used by the space agency's scientists to calibrate its Clouds and the Earth's Radiant Energy System instrument.

Ceres comprises a set of instruments on three satellites that measure the sunlight that is reflected back into space from the Earth and the heat it emits. The amount of sunlight reflected is greatly affected by cloud cover. "If you have no clouds, then clearly you are going to be seeing the Earth's surface," said Lin Chambers, a scientist at Nasa's Langley Research Center in Virginia. "If you are over the Black Forest in Germany, you're going to get very little reflection from those trees. If there's clouds over the black forest, you would get a lot more reflection. Reflection of sunlight is strongly dependent on whether there's clouds there or not."

Since 1997, Chambers's team has worked with school pupils to gather independent observations of clouds, so that Ceres scientists can ensure that the measurements recorded by the satellites tally with evidence from the ground.

Thick cloud cover tends to reflect a large amount of incoming solar energy back to space (pale blue/green/white in the image), but also traps heat in the atmosphere. Photograph: Ceres/Nasa

"Some of the things that cause us real problems are situations like when you have clouds over snow that are really hard to detect from space," said Chambers. "When that happens, you can be off by several degrees, maybe even 10 degrees in terms of surface temperature, which is a pretty substantial error. It's a very localised error [but] it's a pretty substantial error."

In future, anyone using the CloudSpotter app will be able to contribute to reducing those errors. Users take pictures of the clouds they see and send the information to the Cloud Appreciation Society, which identifies the type of cloud. That information, together with time, date and location stamps, is sent to the Ceres team. "What we're hoping to do is tap into that resource and be able to pull out those pictures that actually line up with when our satellites are going over a particular location," say Chambers.

Even if the data from school students and other app users is spread far and wide across the globe, it will be useful for the Ceres team. "You don't have to have a whole bunch of data from a certain place or you don't have to have really good distribution of data, you can kind of pick and choose and use statistics to help you find trends," said Chambers. "We're looking at trends in how the satellite might be missing certain types of clouds or mis-identifying certain types of clouds."