Planetary scientists have known for a long time that several billion tons of water disappear from Earth's atmosphere each year, as if by magic. However, despite having this knowledge, explaining why this happens has turned out to be a very tricky question. Now, Technical University of Denmark (DTU) National Space Institute experts believe they may have found the answer. The most severe loss occurs during the cosmic-ray minimum, they say, when clouds over the ocean lose up to seven percent of their water mass in less than a week, AlphaGalileo informs.

“The Sun makes fantastic natural experiments that allow us to test our ideas about its effects on the climate,” Professor Henrik Svensmark explains. He is the lead author of a new study detailing the finds, published in the latest issue of the scientific journal Geophysical Research Letters. He argues that the loss is prompted by reduced amounts of small aerosols, which occur when solar explosions interfere with the cosmic rays that permeate the Universe. Generated by stellar explosions, these cosmic rays travel at nearly the speed of light, and hit everything in their path with tremendous energies.

When they impact solar emissions in the upper magnetosphere – the protective layer of our planet that prevents us from dying in several ways at once due to radiation in outer space – they apparently strip the aerosols. Without them, water droplets seem to have nothing to adhere to inside clouds. “A link between the Sun, cosmic rays, aerosols, and liquid-water clouds appears to exist on a global scale,” the new study says. “The effect of the solar explosions on the Earth's cloudiness is huge. A loss of clouds of 4 or 5 per cent may not sound very much, but it briefly increases the sunlight reaching the oceans by about 2 watt per square meter, and that's equivalent to all the global warming during the 20th Century,” Svensmark explains.

The team managed to succeed where other investigators failed to discover anything by conducting the investigations at times of Forbush decreases, which are essentially periods of sharp and sudden drops in the count of cosmic rays. “It's like trying to see tigers hidden in the jungle, because clouds change a lot from day to day whatever the cosmic rays are doing,” the expert says. In their experiments, the scientists managed to identify no less than 26 Forbush decreases, since 1987, and then began to analyze their consequences on the clouds. The global link was found using this method.