The missing link between exploding stars, clouds, and climate on Earth
Breakthrough in understanding of how cosmic rays from supernovae can influence Earth’s cloud cover and thereby climate.
The study reveals how atmospheric ions, produced by the energetic cosmic rays raining down through the atmosphere, helps the growth and formation of cloud condensation nuclei — the seeds necessary for forming clouds in the atmosphere. When the ionization in the atmosphere changes, the number of cloud condensation nuclei changes affecting the properties of clouds. More cloud condensation nuclei mean more clouds and a colder climate, and vice versa. Since clouds are essential for the amount of Solar energy reaching the surface of Earth the implications can be significant for our understanding of why climate has varied in the past and also for future climate changes.
- Cosmic rays, high-energy particles raining down from exploded stars, knock electrons out of air molecules. This produces ions, that is, positive and negative molecules in the atmosphere.
- The ions help aerosols — clusters of mainly sulphuric acid and water molecules — to form and become stable against evaporation. This process is called nucleation. The small aerosols need to grow nearly a million times in mass in order to have an effect on clouds.
- The second role of ions is that they accelerate the growth of the small aerosols into cloud condensation nuclei — seeds on which liquid water droplets form to make clouds. The more ions the more aerosols become cloud condensation nuclei. It is this second property of ions which is the new result published in Nature Communications.
- Low clouds made with liquid water droplets cool the Earth’s surface.
- Variations in the Sun’s magnetic activity alter the influx of cosmic rays to the Earth.
- When the Sun is lazy, magnetically speaking, there are more cosmic rays and more low clouds, and the world is cooler.
- When the Sun is active fewer cosmic rays reach the Earth and, with fewer low clouds, the world warms up.
- The climate changes observed during the 20th century
- The coolings and warmings of around 2oC that have occurred repeatedly over the past 10,000 years, as the Sun’s activity and the cosmic ray influx have varied.
- The much larger variations of up to 10oC occuring as the Sun and Earth travel through the Galaxy visiting regions with varying numbers of exploding stars.
- H. Svensmark, M. B. Enghoff, N. J. Shaviv, J. Svensmark. Increased ionization supports growth of aerosols into cloud condensation nuclei. Nature Communications, 2017; 8 (1) DOI: 10.1038/s41467-017-02082-2